Welcome!

This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com


Saturday, September 27, 2014

Ontake, Japan, erupts

Ontake erupts. Photo by andreijejune as cited above.
The eruption started around 11:53 a.m. Saturday, local
time (in spite of the setting in the caption above)
UPDATE SUNDAY: The Japan Times is reporting that 31 people were found unconscious near the peak of Ontake, and that four have been pronounced dead. The BBC is reporting that there were a total of 45 missing climbers. Japanese officials only announce deaths after a formal examination by a doctor. I extend condolences to the families of the victims and missing.

A few hours ago (Saturday), Mount Ontake 155 miles west of Tokyo, erupted, sending a steamy ash plume high into the sky. It last erupted in 2007. News is conflicting about the casualties, but at least one person has been killed,  thirty people have been injured and the Japanese are organizing to rescue an unknown number (reports vary between 41 and 200?) people who were climbing on the mountain. As much as 20" of ash has been reported on the ground near the summit, and Japanese authorities are issuing an alert to stay at least 4 miles away from the summit. The alert level is "3" meaning "do not approach the volcano." Ash is reported to have gone 3 kilometers down the mountain in a pyroclastic flow. There are a number of YouTube videos showing the eruption through cameras held by hikers. Here's one.
From the Kinja Space site cited
in the text and the twitter
user identified above.

Ontake is the second highest volcano in Japan, at 3,067 meters, second to Mount Fuji. There is a nice description of the tectonic setting of Ontake, as well as a collection of eyewitness accounts, at Kinja Space, authored by Mika McKinnon, from which I take much of the following discussion. The author of this blog nicely states that because of geochemical differences in the magmas, volcanoes over oceanic tectonic plates typically have a relatively low abundance of silica (SiO2) and are fairly fluid allowing their gases to escape rather gently (think Iceland, Hawaii). When the eruptions do turn explosive, it is usually because the magma has interacted with groundwater or ice.  Volcanoes that are rich in silica are viscous and gases don't escape easily, leading to conditions that produce explosive eruptions. Such volcanoes usually are found where oceanic and continental plates intersect. The Pacific Ring of fire that stretches up from South America, through western North America and around to Japan is such a setting and eruptions here can be very dangerous. Eruptions of these volcanoes produce flying rocks, volcanic bombs, and hot pyroclastic flows. The movies of the survivors are lucky to be alive.

Ontake had a minor eruption involving water (phreatic) in 2007, but the last major eruption stretched from October 1979-April 1980. In spite of claims that it had erupted in 1892 and 774 AD, detailed examination of the records suggest that this is not true and that it had not erupted prior to the 1979-1980 sequence in recorded history, which is a long time in Japan. Local volcanologists/seismologists Koshun Yamaoka and Shigeo Aramaki are suggesting that the billowing white clouds seen in the eyewitness photos suggest that this is a phreatic eruption.  The possibility that phreatic eruptions are signaling heating of groundwater by rising magma leaves open the scenario of a major magmatic eruption like that of Mount St. Helens that began about 4 hours after the 1980 March-April lateral blast.




Tuesday, September 16, 2014

Mayon and Bardarbunga volcanoes.

Mayon volcano, copyright Tom Tam shot from
Lingnon hill in Daraga Town near the volcano and his home
Mayon, a stratovolcano of nearly perfect symmetry, in the Philippines is again active. It is one of the most active volcanoes in the world. It has erupted 49 times in the past 400 years.  Coincidentally, the most destructive eruption was in 1814, a year before Mount Tambora erupted, with the emission of ash that led to the "Year without a summer" in 1816.  New reports today are that more than10,000 people from around the volcano are being evacuated.

The volcanic activity is being actively reported on Wiki here, and here is the link to the Philippine Institute of Volcanology and Seismology, PHILVOLCS. The monitoring network has detected 39 rockfall events that are "ascribed to incipient breaching of the growing summit lava dome." Continuing seismicity indicates either magma intrusion or volcanic gas activity, and there is sufficient magma in the summit crater to cause a red glow. PHILVOCS has raised the alert level to Level 3, stating that a hazardous eruption is "possible within weeks." A Permanent Danger Zone extends out to a 6 km radius, and an Extended Danger Zone to 7 km. These are being evacuated because of danger of rockfalls, landslides, and lava/ash/mud flows. (Level 3 is the third highest level of alert, following "eruption" and "imminent eruption.")

Bardarbunga in Iceland continues to be active seismically and as of a flyover of the Holuhraun fissure on Sept. 12, about 200 cu meters of magma per second are erupting. Lava is flowing nearly 20 km from the vent.

Wednesday, September 10, 2014

Major solar storm, alert for a CME, coronal mass ejection

Sunspot region 2158, the source of a solar flare today
From Spaceweather.com here
UPDATE 2: From space watch.com:

STORM WARNING (UPDATED): Among space weather forecasters, confidence is building that Earth's magnetic field will receive a double-blow from a pair of CMEs on Sept. 12th. The two storm clouds were propelled in our direction by explosions in the magnetic canopy of sunspot AR2158 on Sept. 9th and 10th, respectively. Strong geomagnetic storms are possible on Sept. 12th and 13th as a result of the consecutive impacts. Sky watchers, even those at mid-latitudes, should be alert for auroras in the nights ahead.

UPDATE 1: I have posted a number of relevant items over the past few years on solar storm activity: 
While our daily earth-weather is filled with heat waves still hitting us as summer fades into autumn, something 'out there' is ready to hammer us! Sunspot region 2158 spat forth a "long duration X1.66 (R3-strong radio blackout) solar flare today. It peaked at 17:45 UTC on Sept. 11  (11:45 a.m. PST on Sept. 10).

This sunspot region has been active for a few months. On September 1 it was the source of a flare, but on the backside of the sun. However, this region is now directly facing the earth. Solar scientists are awaiting data, but they think that it's likely that a Coronal Mass Ejection (CME) of particles will follow.  Information is updated regularly at NOAA's Space Weather Prediction Center here.

Why should we care? A CME has the potential to disrupt electronics that we depend on, whether in space for communications or on earth in health care facilities, computer centers, or communications facilities. A CME can also pose biological risk to astronauts and to passengers and crew in high-altitudes--especially if they are flying cross-polar routes where the particles preferentially come into the earth along magnetic field lines.

According to Mike Wall, a senior writer at Space.com,  the sun "unleashed an X-class solar flare--the most powerful type" today, and it also fired off another intense flare yesterday. Fortunately, NASA in these times of diminishing funding, still has the Solar Dynamics Observatory spacecraft which recorded the event. The flare was an X1.6 storm, and space.com says that it "poses no danger to anyone on Earth or the astronauts living aboard the International Space Station." However, radio communications on earth, the side facing the sun could experience radio communications lasting 'more than an hour.' However, if the eruption is accompanied by a CME, in 2-3 days, there might be significant geomagnetic storms that can disrupt GPS signals, power grids, and  communications.

We are near the peak phase of the Sun's 11-year cycle (Solar Cycle 24), but this phase is the weakest in about 100 years....and that's a whole other discussion!

Monday, September 8, 2014

Meteorite impact in Nicargua: brief report

The crater from the meteorite impact
From this reference
A fragment of the meteorite passing close to earth has made a crater in Nicaragua. I'll post more when I've got some reliable information.

http://www.cnn.com/2014/09/08/tech/innovation/nicaragua-meteorite/index.html?hpt=hp_t2

Monday, September 1, 2014

A fissure near Bardarbunga volcano, Iceland, has erupted

Location of the fissure eruption at Bardarbunga
from www.bbc.com here
On Sunday, a "curtain of fire" developed along a fissure near Bardarbunga, causing a brief alert and a banning of planes flying within 6,000 feet of the volcano. The eruption was described as "calm but continuous."

A detailed chronology of the current activity is being maintained on Wiki. Seismic activity has been continuous, with lava erupting on August 29th in the Holuhraun lava field. The active fissure was about 600 m long, and the entire eruption appears to have been only about 4 hours long. Seismicity quoted down during the eruption, but then returned. On August 30th it appeared that the dyke stopped migrating north, but seismicity continued. Another eruption began at 4:00 a.m. on August 31st, producing a lava flow about 1 km wide, 3 km long, and several meters thick. The flow rate was estimated at 1000 cubic meters/second. Seismic activity is continuing. Updates are posted continuously on the Icelandic Met Office webpage. They've posted the adjacent interesting map showing road closures north of Vatnajokull as a result of the current activity and potential flooding (the hashed area north of the big ice cap).

Saturday, August 30, 2014

The mysterious "sailing stones" of Death Valley

Credits as above. Picture grabbed from ScienceDaily.com.
How can a rock weight several hundred pounds move hundreds of meters across a "dry lake"?  And, why do they move in tandem? One of the early pioneers in solving this mystery was Robert Sharp* of Caltech, and many others have speculated about this problem. Sharp monitored stones over a period of seven years stretching from 1968-1974, and concluded that movement was related to wet stormy weather. Sharp and Carey documented a greatest cumulative movement of 262 m, and "greatest single-episode movement, of 201 m. These were of a small 250 g stone, but other moved stones weighed as much as 25 kg. They concluded that movement "most likely occurs within one to several days after playa wetting, and velocities on the order of 0.5 to 1 m/sec are inferred from track characteristics." Sharp and Carey reported eyewitness accounts of ice sheets containing frozen stones being propelled by wind on other southern California playas, and inferred that the stone tracks at Racetrack were made in this way. However, there were observations that led them to conclude that the stones could not move within extensive ice sheets: they moved out of an encirclement of iron stakes that Sharp and Carey had placed and their spacing changed during movement.
Stationary rocks (blue arrows) and rock moving from left to right (red arrow)

The team used quarried rocks,
one shown here with its
GPS unit
Now, the process has actually been observed by a team led by Richard Norris of Scripps Institute of Oceanography.** In what one of the co-authors, Ralph Lorenz, described as potentially the most boring experiment ever, the scientists outfitted 15 rocks with motion-activated GPS sensors and placed them on the playa to await movement. Only two years into the project, not only did the rocks move, but Norris and Norris were there at the time. When they arrived in December 2013, there seven centimeters (3") of water on the playa, and they concluded that not only must water be present, but it must be deep enough to form "floating ice" during cold winter nights, but shallow enough to leave at least part of the rocks exposed. Panes of ice form during the night, and on sunny days the ice can begin to melt and break up into panels that float across the water if there is wind. These panels actually push the rocks in front of them. The wind speeds were about 3-5 meters/second (10 mph), and the ice that moved was about 1/4" thick.  These speeds are much lower than inferred from track characteristics by Sharp and Carey. The rocks moved at 2-6 meters a minute, and moved for a few seconds to 16 minutes. The rock trails formed under the ice, and became visible only when the water underlying the ice is blown away by winds.

Floating ice moves around the playa under the influence of winds. When it encounters rocks, it may pile up on the upstream side, increasing the effective cross-sectional area of the rocks to both upstream ice and water and thus facilitating movement. On the other hand, sometimes the ice fragments upon encountering a rock. Norris and Norris suspect that this phenomenon might explain the Sharp and Carey observation of the corral behavior: the rock that didn't move out of the corral was just downstream of a stake that may have shattered the ice. Stones with low profiles might be submerged beneath the ice, some rocks may be too big for the available forces under some wind conditions, and others may not totally or partially encounter ice.

But, the researchers concluded, the mystery may not be completely solved: they didn't get to see the really big ones move.

The authors also point out that the sliding rocks are not unique to Racetrack Playa or even the U.S. Ice-driven rock trails are observed on the bottom of Great Slave Lake in northern Canada and on the shores of the Baltic Sea. The mechanism may apply to rock trails on dry lake surfaces in Spain and South Africa where the lakes are at high elevation and exposed to cold winters.

*Robert P. Sharp and Dwight L. Carey, Sliding stones, Racetrack Playa, California, GSA Bulletin, 87(12), 1704-1717.

**Richard D. Norris, James M. Norris, Ralph D. Lorenz, Jib Ray, Brian Jackson, Sliding rocks on Racetrack Playa, Death Valley National Park: First observation of rocks in motion. PloS ONE, 2014; 9(8) e105948 DOI:10.1371/journal.pone.0105948 link to article is here

Sunday, August 24, 2014

South Napa Earthquake today, M 6.0-6.1--geologic context

Building destroyed in Napa. Photo by Justin Sullivan,
Getty Images as published on www.sfgate.com here
UPDATE AUGUST 25: Greg Braswell, as noted in his comment, has published images of the damage and an iso-damage map. They can be found at:


and



Headlines this morning announced that a M6.0 (or 6.1, conflicting reports) earthquake at 3:20 a.m. awoke people around the area of Napa, California, north of San Francisco.  Dozens of people are injured, four homes in a mobile park burned, and damage to buildings in downtown Napa appears extensive. The quake is the largest in the Bay Area since the 1989 Loma Prieta earthquake.

        Here's a bit of context that I found in an on-line technical report authored by John R. Wesling and Kathryn L. Hanson, 2008 (reference at the end of this post). Here is also a link to the USGS earthquake event page.

Map of the five sections of the fault defined by Wesling
and Hanson (Figure 3 from the cited report)
        Napa Valley is a large valley that trends to the northwest. It extends from Calistoga to the southern part of Napa and includes much of the core of the city. The valley is filled with Quaternary alluvial and fluvial deposits from the Napa River system, and earthquake damage in Napa can be especially severe during earthquakes because of shaking of these deposits. The West Napa Fault and its branches were first mapped by Weaver (1949), and subsequent work extended from the 1970's into the 1990's (references in the article cited). This early work reported that the fault and its branches extend 30-35 km along the western margin of the Valley; the Wesling and Hanson report suggests that the fault is 57 km long, extending from Carquinez Strait northwest toward St. Helena. The orientation and geomorphic expression are consistent with the West Napa fault being dominantly a right-lateral slip fault, with some compression that allows development of the nearby mountain ranges. The West Napa fault is one of a series of fairly short faults that include the Franklin and Sothampton faults. These faults lie between the Hayward-Rodgers Creek Fault zone (west) and the Calavaras-Concord-Green Valley fault zone (east).

          Wesling and Hanson divided the fault into five reaches based on geomorphic expression, terrain traversed, and availability and quality of data. These branches are: St. Helena-Dry Creek; Yountville-North Napa; North Napa-Napa River; Napa River-American Canyon; and American Canyon-Carquinez Strait. The USGS is reporting that the earthquake struck 3 miles northwest of American Canyon, and placed the epicenter between 6 miles southwest of Napa, toward Vallejo (see adjacent map). According to the map above, this would place the epicenter on the Napa-River-American Canyon fault toward the northern end or, possibly, the southern end of the North Napa-Napa River branch, depending on where the reference point within Napa city is located.

            No historical earthquakes larger than M6.0 have been associated with the West Napa fault, although the M5.0 Mount Veeder earthquake ("Yountville earthquake") in 2000 may have been linked to it. This earlier earthquake was centered about 5 km west of the West Napa fault, and caused considerable damage in Napa.


Reference: "Mapping of the West Napa Fault Zone for Input into the Northern California Quaternary Fault Database," by John R. Wesling and Kathryn L. Hanson, 2008.

Wednesday, August 20, 2014

Bardarbunga volcano, Iceland, rumbling!

UPDATE: August 23, 2014





__________________________________________




Chaotic ice in Vatnajokull over Bardarbunga
Image from the Smithsonian site here
UPDATE: UPDATE: August 23, 2014. Here is a link to the Icelandic Met Office Bardarbunga information. New information is constantly added at the top of the article.  At 14:10 (Icelandic time), a small eruption of lava was detected under the Dyngjujokull glacier (east of Bardarbunga). Data from radar and web-cams (see this link, for example), have shown no signs of surface activity breaking through the 150-400 meter thick ice. However, the aviation code has been changed from orange to red, though no Icelandic airports have yet been closed. The Icelandic Met office estimates that it could be up to 20 hours before lava breaks through the ice, if it even does. The eruption could remain subglacial. Earthquake activity has continued since August 16. Flooding remains a possibility, with the bridge shown in the picture potentially at risk on the circum-Iceland road.

Earlier in the day, scientists reported that seismic activity indicated that a dyke was propagation as much as 5 miles to the north. On August 21, the dyke was reported to be 25 km long at a depth of 5-10 km. GPS data show that magma is moving.


ORIGINAL POST:

Earlier in the day, scientists reported that seismic activity indicated that a dyke was propagation as much as 5 miles to the north. On August 21, the dyke was reported to be 25 km long at a depth of 5-10 km. GPS data show that magma is moving.


Headlines are starting to appear about seismic activity under Bardarbunga volcano, which lies under Vatnajokull in Iceland, but with frustratingly little information as they hark back on the sensationalism of airplane flights cancelled when Eyjafjallajokull erupted a few years ago. More than 300 people in the region have been evacuated as a precaution. Flooding is a possibility.

 Rather than paraphrasing, here are extracts from the Smithsonian volcano report:

13 August-19 August 2014 

During 13-19 August the Icelandic Met Office reported increased seismic activity at Bárdarbunga volcano. On 16 August more than 200 earthquakes were reported under the NW Vatnajökull ice cap, and GPS stations have shown an increasing signal upward and away from the volcano since early June 2014. On 16 August the Aviation Color code was increased to Yellow. On 18 August the Icelandic Met Office reported an earthquake swarm to the E and another to the N of Bárdarbunga. A M4 earthquake was recorded that was the strongest in the region since 1996. By 18 August there had been 2,600 earthquakes detected at the volcano; earthquake locations from N and E swarms had been migrating NE, but in the evening activity of the N swarm had decreased significantly. That same day the Aviation Color code was raised to Orange. 
Credit: Reuters, as published in bbc.com here


The large central volcano of Bárdarbunga lies beneath the NW part of the Vatnajökull icecap, NW of Grímsvötn volcano, and contains a subglacial 700-m-deep caldera. Related fissure systems include the Veidivötn and Trollagigar fissures, which extend about 100 km SW to near Torfajökull volcano and 50 km NE to near Askja volcano, respectively. Voluminous fissure eruptions, including one at Thjorsarhraun, which produced the largest known Holocene lava flow on Earth with a volume of more than 21 cu km, have occurred throughout the Holocene into historical time from the Veidivötn fissure system. The last major eruption of Veidivötn, in 1477, also produced a large tephra deposit. The subglacial Loki-Fögrufjöll volcanic system located SW of Bárdarbunga volcano is also part of the Bárdarbunga volcanic system and contains two subglacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge to the SW. Jökulhlaups (glacier-outburst floods) from eruptions at Bárdarbunga potentially affect drainages in all directions.

The Veidivötn fissure system, which extends 100 km SW from Bárdarbunga volcano, has been the source of major eruptions during the Holocene. A large, dominantly explosive eruption at about 870 AD from the Vatnaöldur crater row, which extends diagonally across the center of the photo, deposited tephra over much of southern Iceland. The Vatnaöldur eruption originated from a 42-km-long fissure and produced 3.3 cu km of tephra at the time of the settlement of Iceland, forming the the Landnam (Settlement) tephra layer. 

The subglacial Loki-Fögrufjöll volcanic system...glacial ridges extending from the largely subglacial Hamarinn central volcano; the Loki ridge trends to the NE and the Fögrufjöll ridge, seen here, extends to the SW. 

Wednesday, August 13, 2014

Weather extremes, atmospheric rivers and Japanese fire bombs

A shot-down Japanese fire balloon
reinflated by the US
File uploaded by Bkwillwm to
Wikipedia, public domain
     In my book, "The Dynamics of Disaster" (Norton Press, 2013), I discuss the big "rivers in the sky"--our jet streams.  These atmospheric rivers were discovered in the 1920s by Wasaburo Ooishi, a Japanese meteorologist studying the dynamics of the atmosphere near Mount Fuji. To quote my book: The Japanese "were able to turn their knowledge of the jet streams to their advantage during the war by launching balloon attacks on the US, sending 9,000 "fire balloons" aloft to travel thousands of miles east. Some 300 made it to US soil, and six people died when a family approached one and it exploded. (These were the only known deaths by enemy action on continental US soil during World War II.)"
        In a new study by Dim Coumou and a team from Potsdam Institute for Climate Impact Research published August 11 in the Proceedings of the U.S. National Academy of Sciences (ref. below), Coumou points out that the large number of very high-impact extreme weather events over the past decades has seemed out of proportion to the rate of warming of the atmosphere caused by increased CO2. The authors rely on, and quote, an earlier paper in PNAS by Petoukhov, et al. (of the same institute) reporting the same thing: the frequency of these extreme events over the past decade is such that it is unlikely to be just a "stochastic mechanism of extremes."
        And, here's where the Japanese discovery of the jet stream becomes relevant, because it's in the jet stream that the changing flow patterns are driving the weather extremes.

From the cited PNAS article. Shows the increase in so-called "boreal summer weather extremes."
        Again, quoting from my book: "Flowing at the top of the troposphere, the jets have variable elevations between 12,000 and 80,000 feet...[They] can be several hundred miles wide and 1-2 miles deep, and they can flow at speeds of up to 400 mph. Jet stream winds generally flow from west to east, but they have a loopy structure and flow in various directions, even "backward," from east to west, in some segments. The looniness, known as a Rossby wave, has a wavelength of about 1,800-2,400 miles and arises primarily because the Coriolis effect has different strengths at different latitudes. The jets can split apart, re-join, reverse, or simply stop.When the Rossby waves move to the north, they suck warm air northward, e.g., from the tropics into Europe, Russia, or the US. They do the reverse when they move south, transporting cold air from the Arctic to the south.  " I then go on to explain how the position of the jet stream and the Rossby waves influenced the position of Hurricane Sandy in October 2012.
       Now back to the research of Coumou and his team: According to the theory advanced in the article (based on analysis of meteorological conditions from 1979 to 2012), there are resonances in the atmosphere that trap the Rossby waves into certain configurations for long periods of time. Thus, a heat wave that would not be dangerous if it were a few days long, becomes extreme when its duration increases. (The paper is limited to analysis of the Northern Hemisphere.)
     The speed at which a wave travels along the jet stream (the "phase speed")  is, in one approximation, directly proportional to the mean zonal wind speed. To first order, synoptic waves with a wave number (k) equal to 6-8 travel at this speed. The zonal mean wind speed changes with season, being less in the summer. Because the zonal mean wind speed is lower in the summertime, the phase speed is also lower because of this direct proportionality. In fact, in the "boreal summer"--July, August--the phase speed can be close to zero (the waves are quasi-stationary, especially for wave number 6) or even negative (that is, the waves would travel to the west instead of the east). This weakening of the zonal wind speed and, hence, the wave speed is one mechanism explored. Free-traveling waves are simply slowed down or stopped. If the waves are stationary, then the troughs and ridges of the Rossby waves are stationary, setting in the northerly or southerly flow of air for long periods.
        The second mechanism is  the amplification of quasi-stationary waves by resonance between free and forced waves in the midlatitudes. Looking at the Petoukhov et al paper, the quasi resonance hypothesis is as follows. (1) Generally, the large-scale atmospheric circulation at mid latitudes is characterized by traveling Rossby waves with zonal wave numbers (k) equal to or greater than 6 propagating in the longitudinal direction at a phase speed of c~6-12 m/s as discussed in the paragraph above. (2) The circulation is also characterized by quasi stationary planetary-scale Rossby waves with c~0, frequency w~0, and various zonal wave numbers m that develop in response to orographic obstacles or weather sources and sinks, that is, to "conditions in the atmosphere that differ from place to place on the earth. Their hypothesis is that during the extreme summer events, persistent wave structures with high amplitudes evolved and made an unusually large contributions that the usually weak midlatitude response to the thermal and orographic sinks was strongly magnified at wave numbers 6,7 and 8.
     They assert that the apparent cluster of resonance events observed in their data set (see their figure reproduced above) is due to an increased wave 7 and 8 resonances, and that furthermore, these resonances high in the atmosphere are coupled to persistent weather patterns at the surface, and thus the extreme weather events. The changes observed are statistically significant at the 95% confidence level.
        The theory and data (from 1979-2012) suggest that because of warming in the Arctic, temperature differences between the Arctic and tropics are decreasing. Temperature differences drive the atmospheric circulation patterns, and changes in these differences (the temperature "gradients") are causing the atmospheric circulation patterns to change. Although much more detailed work and analyses needs to be done, their tentative projection (Figure 7) of conditions a century away shows t"similarities with the recently observed anomalies). According to RCP8.5 climate model (one in which we don't curb our CI2 emissions very much), the July-August thermal gradients will increase northward of 50N and decrease southward of 50N, leading to strengthening of the sub polar jet and weakening of the subtropical jet.


**I have used the report in ScienceDaily.com for parts of this post: http://www.sciencedaily.com/releases/2014/08/140811170106.htm

The abstract for the Coumou PNAS article is here and the full text is here.

The PNAS Petoukhov et al. article referenced is here.



Wednesday, August 6, 2014

Methane outbursts due to melting permafrost in Siberia: the Yamal crater

Image from the Washington Post here
Update: Of interest may be Alan Weisman's August 12, 2014 article "Why the Earth is farting." Also, see reader comment.

Several months ago, a photo of a crater discovered by a helicopter crew  went viral. It is located in the Yamal Peninsula in Siberia, a desolate spit of land. The crater was variously reported to be 100- 200 feet in diameter. In the July 31 issue of Nature, highlighted in the Washington Post article referenced in the adjacent figure caption, the discovery of two nearby craters is reported in the Washington Post article. The article contains an excellent video taken from a helicopter showing the crater walls actively crumbling. A camera has been lowered to 50 m, and it showed a pool of water at a depth of 70 meters, so the crater extends below 70 m.
Image from Washington Post here

Russian researcher Andrei Plekhanov led an expedition to the crater. He found that near the bottom of the crater (at approximately 50 m depth) air contained concentrations of methane up to 9.6%. That is to be compared to the normal concentration of methane in air--0.000179%. They believe that the abnormally hot summers in Yamai in 2012 and 2013 caused permafrost to thaw. Under the permafrost, usually at depths of 100 meters, methane clathrates are stable. Over the past 20 years, permafrost at a depth of 20 meters has warmed by about 2 C according to the article, quoting Hans-Wolfgang Hubberten of the Alfred Wegener Institute in Potsdam, Germany. Hubberten speculates that a thick layer of ice overlying the clathrates allowed gas pressure to increase until it was great enough to blow out in an explosive burst, forming the crater with rubbly ejecta strewn around it.
     The development of more craters could pose a danger to villages of local reindeer herders, and the craters are only 30 km from a large gas field, the Bovanenkovskoye gas field. A blowout in the gas field cold be very dangerous.

Saturday, August 2, 2014

August 2 Major Landslide in Nepal blocks only route out to the North

Image of the landslide from Ekantipur. This appears to be
a view on the upstream side, with the water from the impounded
river flowing to the right and encroaching on the toe of the slide.
Image from Dave Petley's blog post of August 2, 2014.On
On the night of August 1-2, a large landslide occurred along the Sunkoshi River in northern Nepal, damming the river and creating an urgent crisis. I'm not going to follow this event because Dave Petley's landslide blog will be providing excellent coverage. It is the peak of the monsoon season and so the impounded lake behind the landslide is likely growing fast and, Dave believes, may already be overtopping the dam. It also appears that the dam is in fine-grained materials and so the likelyhood of a breach is high. The valley downstream is heavily populated (evacuation has apparently already begun) and the main road from Nepal into China is blocked. The highway, however, does provide a route to bring in heavy machinery and crews to work on excavating a channel through the slide.

Thursday, July 31, 2014

Los Angeles geyser on Sunset Boulevard!

Back in the 1970's I used to run on the UCLA track near Sunset Boulevard. Two days ago, a 93-year-old water pipe and a 58-year-old pipe broke under Sunset Boulevard near the track, sending a pulsating geyser of water high into the air.  You can view a video of it here (the video symbol in the center of the photo doesn't work because it's just a frame grabbed from the CNN video).

The track was flooded, as well as newly rennovated ($136 million)Pauley Pavilion, the home of UCLA basketball named in honor of the famous coach of winning teams back in the 1970's. At its peak, the broken pipes were sending 35,000 gallons of water per minute onto the streets, with estimates of 20 million gallons released before the flood was brought under control. Maybe the tartan track will survive, the basketball court is questionable. Firefighters had to rescue some people trapped in a parking structure
Flooded track and athletic field at UCLA

If you watch the video, you'll see that the jet is strongly pulsating. This is likely due to an effect known as a "water hammer." The pipeline was a high pressure line, and these lines are subject to very destructive forces due to the water hammer effect (sometimes called a hydraulic shock). These are pressure surges that arise when the water changes direction or momentum.  In the news, you'll see reports that the pipeline had to be shut down gradually--that's because they had to minimize the potential for water hammers. If a pipe is shut off suddenly at the downstream end (where the vent is on Sunset Boulevard), the mass of water upstream is still moving and therefore can build up high pressure.  Such shocks can cause further breakage in the pipelines. (This is common in noisy old water/steam heaters in buildings.)

Photo of Pauley Pavillion
basketball court by Jason McIntyre
I found an interesting set of numbers on Wiki about this effect: "In hydroelectric generating stations, the water travelling along the tunnel or pipeline may be prevented from entering a turbine by closing a valve. However, if, for example, there is 14 km of tunnel of 7.7 m diameter, full of water travelling at 3.75 m/s,[3] that represents approximately 8000 Megajoules of kinetic energy that must be arrested. This arresting is frequently achieved by a surge shaft[4] open at the top, into which the water flows; as the water rises up the shaft, its kinetic energy is converted into potential energy, which decelerates the water in the tunnel."

See the Wiki article for more on water hammers. 


Wednesday, July 9, 2014

Gorgeous Air New Zealand plane! (And, how much can Dreamliner wings flex?)

The new Air New Zealand Dreamliner; photo from CNN.com here
This strays from "Geology In Motion," but I can't resist--the Boeing 787 "Dreamliner" is truly a beautiful plane in flight! It's wings can flex up to 26' (150% of max load).  All aircraft are required by the FAA to be able to withstand at least three seconds of 150% maximum loads (on all structures). In January, 1995, a 777's wings deflected 24' at 154% max load (I couldn't find the actual data to check the facts--I'm using www. flightglobal.com.) Boeing actually did a break test, which you can see in this Boeing produced video. They do not say how flexed it was when it failed, however, only that it was beyond 150%! Here's a cool video (in German) of a lab test showing the flex in a way that you can actually see-it's huge--definitely worth watching this one all the way to the end to see the failure! Here's an explanation that I found on this aviation.stackexchange.com site:

"The amount of flex is really a product of the material. The wing requires a specified ultimate strength; with metal, that translates into a given amount of flex. This can be varied within limits, but it is really the material, its stiffness to yield point ratio, and its fatigue properties, that control how much flex you are going to end up with. CFRP is a very different material, and has much less stiffness for the same yield point, and has essentially no fatigue problems. This is beneficial in that it provides a smoother ride in turbulence; the wing acting essentially like a giant leaf spring. There is some lift lost due to the nature of the curvature, though. However, this is relatively small."

Monday, July 7, 2014

Super-typhoon Neoguri ("racoon") approaches Okinawa

Super-typhoon Neoguri, first super-typhoon of 2014
imaged on July 6 (?) by NOAA/EPA
A quote from my (hard working scientist) friend on Okinawa sent on Monday night, PDT: "The storm has been here since yesterday night. So far nothing comparable to the big storm last year. That one was only category 3 by the time it reached Okinawa, but a typhoon's power is concentrated in a narrow ring around the eye, and last year we were right there in the eye.  The current storm might be stronger but we are only exposed to the outer arms, at least so far, and the effects have been mild. The sound was terrifying last year; now it is merely annoying....I should be working, of course, but I have found that it is not easy for me to work during a typhoon. Perhaps I should try some cooking. I need some pasta sauce, and I have got all the ingredients in the fridge!"


Three inches of rain PER HOUR??? I wonder for how many hours!! Waves up to 14 meters (45')? I have friends on Okinawa and  wish them well (and also asked them to send a first hand report!) The storm is expected to work its way up to mainland Japan by Wednesday. The highest danger is for Miyako-jima, in the center of the archipelago.
     As I write this (Monday a.m. PDT) gusts of up to 270 km/hour (160 miles per hour) are expected, and the Japanese national weather agency is saying that this may be the worst storm in decades. This is the first storm of hurricane season there, and it is apparently hitting rather early in the season. The US evacuated some of its plane from Okinawa in advance of the storm.

Projected path and conditions, from the Japan Meteorological Agency
In my last post, I started by pondering the effect of El Nino on droughts in Japan, but did not address typhoon. But, according to research led by Ryuzaburo Yamamoto at Kyoto University and the Japan Weather Association, El Nino increases the strength of typhoons and increases typhoon-related damage in Japan. The conclusion was based on a study of typhoons over the 48-year period between 1951 and 1999. El Nino's push warm water toward the coast of Peru. Therefore El Nino storms travel further than non-El Nino storms across the Pacific toward Japan, giving them more time over warm waters before reaching Japan.

Damage from typhoons in such years is, on average, three times greater than in La Nina years, even though the average number (16.1) is less than in La Nina years (18.2). Pressures in the center of the typhoons, a measure of their strength, are, however, lower in El Nino years, producing stronger typhoons. The average number of days in which the strength (as measured by the low core pressures) was 46.3 days for El Nino and only 26.9 days for La Nina years. Average storm radius was 235.9 km vs. 180.4 in La Nina years, another measure of the effect of El Nino.

In summary, here, in the last figure, is the Accuweather forecast for the west Pacific for 2014.

Friday, June 20, 2014

Is an El Nino in the offing?

The record of La Nina's and weak El Ninos that
have occurred since the
last powerful El Nino in 1997-1998. From the
Nikkei Asian Review cited in the text.
The Nikkei Asian Review had an interesting article on June 12 saying that, although it is too early for certainty, there are hints of an El Nino this winter, and perhaps an El Nino that will be as strong as the one of 1997-1998. Since an El Nino means a cooler summer in Japan, it could portend a problem for rice growers in Japan.
     What has caused this speculation? Normally the trade winds blow from east to west, but in January and February there were two strong westerly bursts, followed by two "slightly less powerful" ones in March and April. If such bursts continue and develop into a reversal of the trade winds, an El Nino will occur. Warm surface waters of the Pacific will be pushed easterly toward the west coast of South America.
     Although highly speculative at present, a switch back to El Nino conditions may have significance in the bigger picture. La Nina conditions have permitted storage of heat in the deep waters of the Pacific. Storage of heat in the ocean takes it away from the atmosphere, keeping global warming in check. The haitus in global warming in recent years may be due to this string of La Nina events. A switch back to El Nino conditions, particularly if they last a decade or more as is common, could result in a resumption of global warming conditions. Here's a link to a Slate article on the possibility, and here's Cliff Mass's comments about it, as well as the quality of forecasts made in April, the time of these two articles.
Typical El Nino weather conditions. From here.
     The June 5 ENSO Diagnostic Discussion issued by the Climate Prediction Center says that the chance of El Nino is 70% during the Northern Hemisphere summer and 80% during the fall and winter.
     The Asian Review article also notes that because of budget cutbacks, 24 of NOAA's 55 ocean buoys in the tropical Pacific are unable to operate and send data needed for monitoring the situation.

Monday, May 26, 2014

Massive mudslide in Colorado on Sunday, Memorial Day weekend

The Sunday, May 24, Mesa County Mudslide. Dimensions
are uncertain, but at least 0.5 mile wide, 2-3 miles long, and
250 feet deep. Photo by Aaron Ontiveroz, Denver Post
as published here.
UPDATED: May 26 and May 28, 2014

Heavy rain again (after Oso and Afghanistan) appears to have triggered a massive mudslide, this time in the Grand Mesa country of Colorado. The location is 11 miles southeast of Collbran, about 40 miles east of Grand Junction. The area is remote, cell coverage is sparce to nonexistent, and news is just starting to break of this event. More than 3/4" of rain hit the area on Sunday.  Three men, locals who had gone into the area to investigate the possibility of a smaller slide when they noticed problems with their irrigation water, are missing.

Update May 26: Weather.com meteorologist Jon Erdman said that Grand Junction picked up 0.42 inches of rain on Sunday, and that higher totals atop Grand Mesa above the slide were likely Heavy rain is expected toward the end of the week and into the weekend, making the slide area still very dangerous.

Location of Collbran ("A") relative to Grand Junction
This slide (dimensions in figure caption) is significantly larger than the Oso, WA, landslide which measured about 1500 feet wide, 4400 feet long, and 30-70 feet deep. The area is on U.S. Forest Service and private land. No structures or major were involved. The sheriff has reported that the person who reported the slide heard a sound like a freight train, and that "the slide came down with so much force and velocity that it came to a hill and went up and over a hill and then came back down--a significant hill." The area remains unstable as of this writing (2:30 PDT, Monday).

Another photo of the mudslide taken by Aaron Ontiveroz
as found here.
The area where the landslide climbed a hill is at the
upper right of this image. It is at a sharp bend in
the path of the flow. Photo also by Aaron Ontiveroz,
Denver Post.
I couldn't find any references to previous slides in this area, but did find a 2013 paper entitled "Characteristics of Landslides in Western Colorado, USA", focused around the Somerset-McClure Pass area only about 50 km away (as the crow flies, a lot longer by any access roads as they are separated by the Grand Mesa National Forest and some rugged country.) The authors of this paper are N.R. Regmi, J.R. Giardino, and J.D. Vitek, and it is published in Landslides, on-line 05 June 2013. The Colorado Geological Survey also has an extensive website and inventory program that can be viewed here. It is painfully clear that western Colorado has major landslide problems.

Update 5/26: Geologist Jonathan White, with the Colorado Geological Survey, said that another slide seems inevitable because of the buildup of water in a depression created by the big slide. The depression that he's referring to may be (???) at the top of the slide in the lower photo. Water has been flowing into the depression already, but White says that it's impossible to tell when the next slide could occur--perhaps even years from now when people have forgotten the danger. The terrain is too unstable for any work to drain the water, and Jonathan Godt, a geologist with the USGS says that "practical engineering measures for things of this size are pretty limited."

Update, May 28: The last photo in this set shows the mobility of the flow as it climbed up and over the ridge in the upper right where it took a sharp right turn in the flow path. From a topo map of the area, it looks like the elevation of the headwall at its crest is roughly 9700 feet, and that the elevation where the slide began the right-angled turn is about 8000 feet. This drop of 1700 feet elevation occurred over about 1.5 miles. It looks like the topped a ridge that is a couple of hundred feet higher than the valley bottom (where it spilled over the ridge on the right side as viewed in the photo, left side when viewed from the flow direction). Since the slide was reported to be several hundred feet thick, it's not clear how much of this spill-over was due to the energy of the flow versus the thickness of it as it approached the ridge. Note the erosion line of the trees in the extreme upper right of the photo and how it appears to be close to the elevation of the top of the overtopped ridge. This suggests to me that the overtopping had a significant contribution just due to the huge thickness of the flow.

There is also a very unusual change in texture between the material that did not go up the hill (streamwise right) and the material on the proximal side of the hill (rough vs. smooth?), and I'm wondering if bigger particles in the flow got left behind as the more fluid finer-grained material climbed the hill? Did the flow climb the hill on its left side (toward the top of the photo) and then fall back toward the valley on its right side (the smooth area on the right side of the ridge)? Is it possible that the "slide" changed to a muddy flow at this point--certainly there is a change in the texture of the slide downstream from this area, as pointed out today by Dave Petley on his AGU landslide blog. Field observations will be needed to clarify many questions.

After making the first turn to the right, the material then turned to the left, spread out around and over a region of ridges (emanating from the hill on the streamwise right side of the flow in the middle of the photo), and eventually exited from the main channel, narrowly missing a developed site of some sort (natural gas, fracking facility??).  I'm not sure what this is, and the WWW is full of speculation. The elevation of the toe of the slide is about 7300 feet, making the total drop of the order of 2400'.




Friday, May 23, 2014

Camelopardalid meteor shower

In the lower right half of the image you can see the shape
of a giraffe and the location of the Camelopardalids meteor
shower tonight. Courtesy Science@NASA.
In the early hours of the morning May 24 (3-4 a.m. EDT and midnight and 1 a.m. PDT), a meteor shower from Comet 209P/LINEAR will dazzle observers with up to 1000 meteors per hour. This is a new shower, occurring five days before Comet 209P/LINEAR makes its closest approach to the earth (8 million kilometers) on May 29. The earth passes through the comets orbit, which is strewn with debris shed from the comet on previous passes. Amateur and professional observers are excited about the potential for this to be a "meteor storm", levels of 1,000 per hour, and many will be at telescopes or out on the lawn with pencil and paper counting them.
Plot of the Earth's path through the meteor shower
by Jeremie Vaubaillon.

Comet 209P/LINEAR was discovered on Feb. 3, 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR) research project. It orbits around the sun with a period of roughly 5 years, with an aphelion out near Jupiter's orbit. As a result, calculations show that its orbit has been perturbed by the gravitational pull of Jupiter over the past few centuries, at least as far back as 1798. Most particles in the shower are smaller than a grain of sand and burn up high in the atmosphere.

Scientists are being cautious, predicting a few hundred meteors per hour to be on the safe side, but almost all of them express hope for the storm-level of 1000 per hour. Comet 209P/LINEAR is a small comet, and has in recent passes near the earth, a fairly low dust production. Observers in the United States and southern Canada are in the best position to see the shower.  The moon is a waning crescent, just four days from the dark new phase and will not be a hindrance.

Fred Whipple first developed the idea that comets were "dirty snowballs" orbiting the sun.The meteoroids are formed when a comet passes by the sun and some of the ice (water, methane, ammonia or other volatiles) sublimates, releasing the small silicate particles bound in it. The meteoroids spread out around the comet, eventually, after many passes by the sun, filling in the entire orbit.

Here is a link to Mikhail Maslov's website on the 2014 meteor shower, and here is a post by Robert Lunsford.

Sunday, May 4, 2014

Afghanistan landslide of May 2, 2014


The Badakhshan landslide, showing its extreme mobility
Photo by Blal Sarwary as posted on Dave Petley's Landslide Blog
Links to sources are in adjacent text.
Our thoughts and condolences are with the survivors of the devastating landslide in Afghanistan.

On his Landslide Blog, David Petley has drawn from the Twitter feed of Bilal Sarwary, a BBC reporter on the spot where the landslide occurred in the Argo District of Badakhshan Province in Northeast Afghanistan was a failure in deposits of windblown sand (loess) after a period of heavy rainfall and flooding. With no hope of recovering the bodies of victims, Afghanistan has declared the site a mass grave and dedicated Sunday as a day of national morning.

While Petley conservatively says that "is now believed to have killed at least 350 people," the news media are reporting as many as 2000 deaths. Even the conservative value makes it the worst landslide to date in 2014, and the death toll is bound to increase as reports of missing people come in. There are about 4,000 survivors in need of care. The landslide is believed to have occurred in two phases, separated by enough time that people from adjacent villages had arrived to help with rescue efforts, only to be caught by the second landslide. Note that the Oso landslide in the U.S. two months ago also had two phases, but these were separated only by about 4 minutes.

Location of the landslide
From Cnn.com here
Petley based his conclusion that the landslide had occurred in loess on the high mobility of the landslide shown in the photo above, and the observation that there are no large boulders visible in the photo, an indication that the sediments were probably wind-laid. Landslides in loess are not unknown in this part of the world, though much more reported from China than Afghanistan. Loess covers huge areas of the world (see map), including some that are prone to large earthquakes (up to M8.5), such as this part of Asia. Loess covers 6.6% of the total area of China. In the middle part of the Yellow River in China, it can be 1000' thick. Chinese scientists have pioneered may of the studies of loess failure.

Map of location of loess deposits from here.
Loess was deposited during the Pleistocene by winds blowing across deposits of the receding glaciers. The climate was dry and, in many areas of the world, such as China and Afghanistan, has remained relatively arid since the loess was accumulated.  It is highly porous and has a weak cohesion, giving it rather unusual geological engineering properties.* It can contain up to 20% water in so-called "macropores", see photo. The mosaic structure of loess gives it strength, but the existence of macropores makes the strength vulnerable under seismic shaking or heavy rains. When loess fails due to heavy rains (or over-irrigation), it is because the pores fill with water, destroying the strength of the soils. However, even relatively dry loess has been known to fail.
Macropores in loess, Tianshui, Gansu Province
from the Zhang reference cited at *


There are a number of ways in which landslides can be triggered in loess areas. Zhou et al. (2002)** have classified loess landslides according to three "indicators": (1) the landslide material; (2) the position of the surface along which the slide moves; and (3) the mechanism of movement. Landslide materials can be either loess alone, or loess and underlying soil/rock, such as laterite, which is common in this part of the world. The development surface can be solely within the loess, or within the loess and underlying soil/rocks. The mechanism of movement can be slow gliding, or "collapsing-gliding." They point out that (in China, but I'm assuming that this applies to Afghanistan), landslides occur in (a) the rainy seasons of July, August and September, and (b) the ice melting period of March, April and May. This Afghanistan slide, if triggered by heavy rains, has occurred early compared to to the (Chinese) rainy season.

Water affects/causes landslides in three different ways: rainfall, surface water, and ground water. Both rainfall and surface runoff can increase the water content of a hillslope, and even saturate it. When saturated, e.g., below the water table, the cohesive force of the soil and the frictional force of layers within it can greatly decrease. Surface water also erodes the topography, particularly in tectonically active areas of the world. This leads to unstable, steep slopes prone to landsliding. Changes in groundwater affect the mechanical characteristics of soil. For example, when water content of soil increase up to 35%, shear-resistance decreases by 60% (Zhou et al., page 160). Ground water can also dissolve components of the soil, changing its composition and strength. 

Zhou et al** point out the potentially large influence of humans on inducing landslides. Remembering that this article was written in 2002, so that the statistics are not current, they report that in the 20 years preceding their report, population had reached 81.49 million, accounting for 7.8% of the nation's population. With this increase of population, "irrational human activities" such as excavating foothills, filling hillsides, and over-cultivating accelerated natural disasters. Because industry is relatively sparse in these loess areas, the output of industry and agriculture was below the national average, accounting for 6% of that of the nation. These areas tend to be poor, and frequent natural disasters "are major factors hindering the social and economic development of [the] loess area." On the borders of the loess plateau, flat ground is rare and slopes are universally leveled to build houses, and many people live in cave-houses cut into the slopes. All of these activities reduce the support at the bottom of the slope and decrease its stability. Vegetation, that normally stabilizes a slope, has been heavily impacted since the 1950's by deforestation. 


ASIDE: Although there appears not to have been an earthquake that triggered the Afghanistan landslide, it is worth keeping in mind that this huge region in Asia is subject to major earthquakes, which commonly trigger landslides if they are greater than M6, and wet weather.

COMMENT ADDED APRIL 6: John SanFilipo has commented that "There was a small (?) quake just west of the slide area near Rostaq reported on 12 April. Thanks, John! It will be interesting to see if anyone looks for a cause and effect.

On December 16, 1920, the M7.8 Haiyuan earthquake (also called the 1920 Gansu earthquake and estimated by some to have been as high as M8.7) killed at least 100,000 people, probably double this number according to the USGS. A Chinese paper in existence at the time Ningxia Daily, reported 240,000 killed. Strong trembling occurred for 10 minutes. Reportedly, 500,000 houses and cave dwellings collapsed.* The shaking occurred over an area of about 50,000 square kilometers, most of which is covered by loess. The landslides triggered by the earthquake blocked rivers and buried villages and farmlands.

There are several prominent consequences of earthquakes. (1) Fissures are produced both near the fault and far away from it. Near the fault, the fissures are primarily related to tectonic deformation and are spread on both sides of the fault. However, in zones of weak shaking far away from the fault (all the way through much of the loess region in China) fissures can be formed by subsidence in the loess caused by the loss of strength of the loess when it is shaken (liquefaction). (2) Landslides occurred in three types of areas in the Haiyuan quake: (1) near or in the high intensity shaking zone. However, because the soil cover was thin in this region, the landslides were quite small. (2) In an area of moderate shaking, more than 1000 sq. km. in area, there were 650 landslides reported (see the Zhang ref below), and 41 of them dammed rivers to form so-called "barrier" or "quake" lakes. These slides were big because the area was hilly and covered with loess ranging from 20-50 m (66-165') in thickness. (3) More distal regions where the damage caused by the landslides was more severe than that caused by the shaking of the quake itself. This area covered another 1000 sq. km.



*Zhang, Zhenzhong, Geological disasters in loess areas during the 1920 Haiyuan earthquake, China, GeoJournal, 36 (2/3) 269-274, 1995.

Zhou, Jin-xing, Zhu Chun-yun, Zheng Jing-ming, Wang Xiao-hui, Liu Zhou-hong, Landslide disaster in the loess area of China, Journal of Forestry Research 13(2), 157-161, 2002.

Friday, April 18, 2014

Mexico's 7.2 earthquake and it's early warning system

Seismic record from the Guerrero April 18 earthquake
From Earthquake-Report.com 
Note on May 4: I am very grateful to Jenda Johnson who pointed out an obvious typo--I had reversed P and S waves in the third paragraph! Sometimes the mechanics of doing this blog just numb out the brain! Thanks, Jenda!

A magnitude 7.2 earthquake struck in the Acapulco/Mexico City region early this morning, a Good Friday holiday morning when many residents had apparently slept in or gone away on vacation. The earthquake lasted about 30 seconds. The epicenter was in the state of Guerrero, north of Acapulco. The U.S. Geological Survey has an automatic damage estimator here. The USGS estimates deaths between 1-100, and economic losses between 1-100 million; Max Wyss's estimator at WAPMER predicts 0-50 killed. In spite of damage reports there have been no reports (10 hours later) of fatalities, so there are likely to be very few if any as more information comes in. Why?

One reason that many buildings in the area are built to be quake-resistent because of the history of previous earthquakes. But another reason is that Mexico has an early warning system for earthquakes, and the news has reported that a warning went out about 2 minutes before the quake (I have not been able to independently verify this).

Mexico instituted a Seismic Alert System (SAS) for Mexico city as an experimental project in August 1991. By monitoring the arrival of the faster compressional ("P") waves, warnings can be issued before the arrival of the stronger shear ("S) waves. The system gives, on average, about 60 seconds warning for earthquakes generated in the Guerrero Gap. The quake was the result of a thrust motion where the Cocos plate is being subducted below the North American plate at a rate of about 65 mm/year. The Guerrero Seismic Gap is a ~200 km long segment of this plate boundary that has experienced no significant earthquakes since 1911 (M7.6 at that time). It is thought that an earthquake of magnitude greater than 8 is possible if the entire gap were to rupture at the same time.

The development of the SAS was sponsored by the Mexico City Government, beginning operation in 1991. By the end of the first year, it was experimenting with providing warning to some public elementary schools, and was opened as a public service on commercial radio stations in 1993 after a successful alert that gave 65-73 seconds advance warning during two Guerrero earthquakes (M5.8 and M6) on May 14, 1993. Extensive planning for dissemination and education for the public followed. By 1998 the SAS detected 681 seismic events, 12 of which were strong enough to trigger the general early warning signals in Mexico City, one false one, and one earthquake well detected, but not warned. In the one false alarm, phenomena that were feared--such as panic that could cause injuries--did not occur, but it was realized that many members of the public had not been trained, and training of the public remained a high priority.

The advantages of an early warning system are numerous: Casualties and fatalities are reduced by making people aware that strong ground shaking is imminent. Tsunami calculations can be initiated earlier. Traffic such as trains or subways can be stopped or slowed. The disadvantages or risks are the alerts may not be quick enough  in areas close to the focus of the earthquake and subjected to strong shaking, that there can be false alarms, and that the technique is not good if there are multiple earthquakes close in time or location. Hence, there are tradeoffs between speed and accuracy. Continuous citizen education and awareness must be maintained, and a wide variety of channels of communication must be used to ensure wide dissemination. The private sector must be incorporated into the early warning system so that appropriate services/operations can be shut down for safety.