Sunday, May 31, 2009

North Korea nuclear test seismogram - crustal phases

Back on January 17, I had an entry on crustal phases. We should do a short review to understand the nomenclature shown in the diagram in the last blog for the seismic phases seen on China seismograms after the Korea nuclear test.

You can find a listing of seismic phases here.

Note in particular the phases shown in the previous quake observed for the NK nuclear test:
  • Pg - at short distances, an upgoing P wave from a source in the upper crust; otherwise, a wave refracted from a mid-crustal discontinuity
  • Pn - a P wave refracted along the crust-mantle boundary
  • Sg - at short distances, an upgoing S wave from a source in the upper crust
  • Sn - an S wave refracted along the crust-mantle boundary
Rayleigh and L waves are surface waves.

Friday, May 29, 2009

North Korea nuclear test seismograms

Story and image from LDEO:

Seismologists who have intensively studied North Korea’s nuclear testing efforts say Monday’s blast was certainly a nuclear bomb, roughly five times larger than the country’s first test in 2006. The scientists, at Columbia University’s Lamont-Doherty Earth Observatory, say signals picked up by seismic stations including one in China close by, showed clear characteristics of a shallow underground nuclear explosion, with a force of probably several kilotons.

“The second test appears to have a significantly higher yield,” said seismologist Paul G. Richards, a longtime expert on seismic detection of nuclear tests. He and his colleague Won-Young Kim, also at Lamont, are coauthors of articles on the 2006 North Korean test in Nature Physics and Eos Transactions, and have a piece on current advances in nuclear-test detection in the March 2009 Scientific American.

Reports so far have given varying estimate of the explosion's size, and many suggest that only eventual leakage of radioactive particles into the air will confirm that the explosion was nuclear, not chemical. The assessment by Richards and Kim is in line with an anonymous Obama administration official who told The New York Times shortly afterward that it was a nuclear blast of “several kilotons.”

The seismic pattern produced by the latest blast was nearly identical to the Oct. 9, 2006, North Korean test, which later leaked radioactive particles. “The seismogram is almost a carbon copy of the previous image,” said Kim. Seismograms show two sudden, sharp jolts, followed by an angry buzzing of the earth. The dominant seismic waves produced were fast-traveling compressional, or P-waves, which alternately compress and dilate the ground outward from the source--the signature of an explosion. Earthquakes, by comparison, usually start out with weaker P-waves, and produce more shear waves, which shake the ground sideways in relation to their direction of travel. Kim said analysis of signals collected by different stations located the explosion in the same mountainous test area where the last test took place, some 40 kilometers northwest of the city of Kilju.

Richards said it was “implausible” that the blast, which produced shaking equivalent to an earthquake of magnitude 4.5 to 4.7, could have been made by surreptitiously planted conventional explosives. The explosion’s size cannot be exactly quantified because seismic measurements are influenced by the depth of the explosion, and the type of material in which it takes place. Geologic maps show that the surrounding area is made of hard granite and other rocks that transmit energy efficiently, but no one except the North Koreans knows the depth of the blast, nor whether it was in direct contact with bedrock. Kim put the blast in the range of 2.2 to 4 kilotons (a kiloton is equal to 1,000 tons of TNT). By comparison, the 2006 test was estimated to be less than a kiloton, and was considered by many to be only a partial success that did not completely detonate.

Other estimates of the current test have ranged widely. The Russian Defense Ministry said it might have yielded 15 or 20 kilotons—the size of the bombs that leveled Hiroshima and Nagasaki—while European scientists have estimated three to eight kilotons. However, some of these other estimates were made using data from stations far from the source, or which did not have readings from the 2006 event to use as a baseline. Richards and Kim took data only from a handful of stations that monitored the 2006 test, as well as earlier known chemical explosions and natural earthquakes in the same area that could be used for comparison. This included readings from the closest station from which data is available, in Mudanjiang, China, some 370 kilometers north of the test site. Much Chinese seismic data is unavailable to other countries, but Mudanjiang, operated with the U.S. Geological Survey and an international consortium of universities, transmits readings to researchers worldwide almost in real time. Kim and Richards also obtained information on signals from stations in South Korea, Australia, Alaska and Kyrgyzstan. Each showed amplitudes three to seven times higher than in 2006, leading to the conclusion that the new test had a yield roughly five times larger than the previous one.

By any account, the latest test blast was small compared with the bombs now stocked by major countries including the United States, which run upward of 50 megatons. But, said Richards, “Even the 2006 North Korean test would have been a disaster if it had gone off in a metropolitan area. This one was bigger.”

Wednesday, May 27, 2009

North Korea nuclear test, like m=4.7 earthquake

Underground nuclear tests generate seismic waves like earthquake. Properties of the seismic waves generated by these two mechanisms allow these types of events to be distinguished.

The seismogram of this event to the right is from the BBC.

According to the U.S. Geological Survey:

The shallow, magnitude 4.7 seismic event that occurred on 25 May 2009 at 00:54:43 UTC is linked to the claim of a nuclear test by North Korean officials. While the USGS cannot positively identify the seismic event as a nuclear test, it was shallow and located in the vicinity of the 9 October 2006 North Korean nuclear test (magnitude 4.3). Moreover, comparison of the seismograms of the 9 October 2006 and 25 May 2009 events at individual seismic stations shows similar features, suggesting that the two events are in close spatial proximity and are the same type of source, although the more recent event is larger.

Location41.306°N, 129.029°E
Depth0 km (~0 mile) set by location program
Distances70 km (45 miles) NNW of Kimchaek, North Korea
95 km (60 miles) SW of Chongjin, North Korea
180 km (115 miles) SSW of Yanji, Jilin, China
375 km (235 miles) NE of PYONGYANG, North Korea
Location Uncertaintyhorizontal +/- 3.8 km (2.4 miles); depth fixed by location program
ParametersNST= 75, Nph= 75, Dmin=371.4 km, Rmss=0.57 sec, Gp= 72°,
M-type=body wave magnitude (Mb), Version=A

More on nuclear tests and seismic waves to come.

Thursday, May 21, 2009

An earlier Niagara earthquake

Photo from NY State

Coincidentally, the week of the Buffalo quake mentioned in the last blog, the Niagara Falls Reporter recalls an earlier quake in the region.

And, on Saturday, I'll be driving through Niagara Falls on my way to the AGU in Toronto.

By Bob Kostoff

This area seems to have lucked out by never experiencing a major earthquake, at least within recorded history. But we have had a few minor tremors from time to time because we do exist in a fault area.

Mostly the tremors just caused some frayed nerves and perhaps a few broken dishes that were rattled off shelves and tables. A couple of incidents were reported in the spring of 1897.

The local newspaper reported in a headline on March 6, 1897, "And the earth trembled."

The report went on to say that area residents were startled at about 10:40 p.m. on March 5 by the rumbles, which were told in a number of headlines as "This city was included in a belt that was shaken severely by a well defined earthquake at 10:40 o'clock last night" and "Windows and dishes broken."

People were rattled and shaken "for miles about between here and Lake Ontario" and it was felt worst below "the mountain ridge. On the Indian Reservation, the Indians were all alarmed." Not to be outdone, "Lewiston and Youngstown residents were frightened," and the trembles caused equal concern in areas of Canada.

At first, the populace was perplexed. The newspaper said, "What was it? A question on everybody's lips this morning. It came over telegraph and telephone wires and down the streets. It fairly howled its way along, but no answer came."

Of course, seismic information was not as sophisticated in those days.

At first, the report said, "the general opinion was that some terrible explosion has occurred."

It must have been a pretty powerful tremor, because "it was so severe that police at the No. 2 Police Station thought a bank had been robbed near them and they investigated, but investigated in vain."

The newspaper office even then was the place to go for information, so reporters fielded a myriad of phone calls from Lewiston, Youngstown, and even from Thorold and St. Catharines in Ontario. The inquiries "were about some explosion that occurred here."

The paper noted, "There are several powder magazines in the vicinity of this city and these were examined and found to be all right. The mystery deepened."

An exhaustive search was made for some building blown to smithereens, but nothing was found.

The newspaper reported, "The shock was so sharp, sudden and short that no one thought of an earthquake."

When no other explanation could be found, citizens began believing an earthquake had occurred here.

A short time later, on May 28, 1897, the newspaper reported in a series of headlines, "Visit of an earthquake. This city included in a broad belt of country that was shaken last night. Many startled in Buffalo. The quake felt eastward into Vermont and north to Montreal. The shock here was rather light but a number noticed it. No damage done." This time, the report said, "thousands of people recognized it at once" as an earthquake. "The quake was distinguishable here in Niagara Falls, though the shock was slight."

Residents of Lockport felt the shock more distinctly. The tremor "rattled windows and blinds."

But in Niagara Falls, such noise was becoming commonplace. The newspaper reported that the quake "was very similar to the effect of heavy blasts in the Tunnel District, which are so frequent that no attention is paid to them."

The tunnel referred to is the one dug from the upper river under the city to the gorge so falling water could turn turbines and generate electrical power.

Wednesday, May 20, 2009

Small earthquakes in Albany, NY

Back to the East Coast. From LCSN:

Recent Earthquakes in the Northeastern U.S.

A minor earthquake occurred at 8:53:29 PM (EDT) on Sunday, May 17, 2009 .
The magnitude 3.0 event occurred 32 km (20 miles) SW of Albany,NY.
The hypocentral depth is 9 km ( 6 miles).

Magnitude 3.0 - duration magnitude (Md)
Time Sunday, May 17, 2009 at 8:53:29 PM (EDT)
Monday, May 18, 2009 at 0:53:29 (UTC)
Distance from Albany,NY - 32 km (20 miles) SW (232 degrees)
Schenectady,NY - 34 km (21 miles) SSW (206 degrees)
Pittsfield,MA - 84 km (52 miles) WNW (295 degrees)
Coordinates 42 deg. 34.3 min. N (42.571N), 74 deg. 6.7 min. W ( 74.112W)
Depth 9 km (5.6 miles)
Quality Fair
Location Quality Parameters Nst= 24, Nph= 49, Dmin=27.3 km, Rmss=0.21 sec, Erho=0.2 km, Erzz=0.5 km, Gp=72 degrees
Event ID# ld1023914

Tuesday, May 19, 2009

Mount St. Helens seismogram, May 18, 1980

Note the harmonic tremors in the bottom half of the record, which are characteristic signals accompanying magma rising through a volcano.

But the event at 15:32 GMT (8:32 am Pacific time) is the quake that accompanied the main blast.

From the U.S. Geological Survey:

Within 15 to 20 seconds of a magnitude 5.1 earthquake at 8:32 a.m., the volcano's bulge and summit slid away in a huge landslide - the largest on Earth in recorded history. The landslide depressurized the volcano's magma system, triggering powerful explosions that ripped through the sliding debris. Rocks, ash, volcanic gas, and steam were blasted upward and outward to the north. This lateral blast of hot material accelerated to at least 300 miles per hour, then slowed as the rocks and ash fell to the ground and spread away from the volcano; several people escaping the blast on its western edge were able to keep ahead of the advancing cloud by driving 65 to 100 miles an hour! The blast cloud traveled as far as 17 miles northward from the volcano and the landslide traveled about 14 miles west down the North Fork Toutle River.

The lateral blast produced a column of ash and gas (eruption column) that rose more than 15 miles into the atmosphere in only 15 minutes. Less than an hour later, a second eruption column formed as magma erupted explosively from the new crater. Then, beginning just after noon, swift avalanches of hot ash, pumice, and gas (pyroclastic flows) poured out of the crater at 50 to 80 miles per hour and spread as far as 5 miles to the north. Based on the eruption rate of these pyroclastic flows, scientists estimate that the eruption reached its peak between 3:00 and 5:00 p.m. Over the course of the day, prevailing winds blew 520 million tons of ash eastward across the United States and caused complete darkness in Spokane, Washington, 250 miles from the volcano.

During the first few minutes of this eruption, parts of the blast cloud surged over the newly formed crater rim and down the west, south, and east sides of the volcano. The hot rocks and gas quickly melted some of the snow and ice capping the volcano, creating surges of water that eroded and mixed with loose rock debris to form volcanic mudflows (lahars). Several lahars poured down the volcano into river valleys, ripping trees from their roots and destroying roads and bridges.

The largest and most destructive lahar was formed by water seeping from inside the huge landslide deposit through most of the day. This sustained flow of water eroded material from both the landslide deposit and channel of the North Fork Toutle River. The lahar increased in size as it traveled downstream, destroying bridges and homes and eventually flowing into the Cowlitz River. It reached its maximum size at about midnight in the Cowlitz River about 50 miles downstream from the volcano.

Note the sequence of events: thge earthquake first, the landslide next, and then the uncorked volcano blew its stack.

Monday, May 18, 2009

Mount St. Helens, May 18, 1980

Twenty-nine years - how time flies!

"Graphs show average number of events occurring per day (blue) and average seismic strain energy release (square root of seismic energy) per day (red). The times and types of eruptions are shown at the top of each figure with the length of the symbol roughly proportional to the size of the eruption. Magmatic explosive eruptions are those which had a significant amount of new, juvenile magma ejected into an ash cloud. Phreatic explosions are steam or gas explosions involving little or no magmatic material. Dome growth eruptions are relatively quiet, non-explosive eruptions of lava onto the lava dome.

"This plot is for the explosive eruption period of 1980. The first phreatic eruption occurred on Mar. 27, 1980 and the cataclysmic avalanche, lateral blast and plinian ash eruption occurred on May 18 1980... In the 1980s the sensitivity of the seismic network was much less than it is today and thus only larger earthquakes were located. During the pre-cataclysmic eruption period before May 18 over 600 earthquake greater than magnitude 3 were located and 12 around magnitude 5. During this same period, both because of network sensitivity but also because the seismic noise level was so high that small earthquakes could not be well recorded, there were only 6 events located with a magnitude less than 2.

"After the major eruption on May 18 the seismic noise level was usually much less and smaller earthquake could be more easily located, thus the energy plot after May 18 is very small while the number of events continues to have bursts of activity at moderate levels. "

I like the multidimensional data on the graphs.

Half a lifetime ago (for me).

Friday, May 15, 2009

Latest small quakes in Dillsburg, PA

From LCSN:

A minor earthquake of magnitude 1.3 occurred in Dillsburg,
Pennsylvania (23 km southwest of Harrisburg, Pennsylvania).

There are felt reports from Dillsburg, PA.
There were a number of foreshocks and aftershocks reported.

Origin time: 5/11/2009 01:18:23.1 EDT
5/11/2009 05:18:23.1 UTC
Location: 40.088 N, 77.001 W Depth= 1 km fixed
(40 deg 5.3 minutes North, 77 deg 0.1 minutes West)
Magnitude: Mc=1.3

Only one aftershock was locatable:

Origin time: 5/11/2009 01:34:02.6 EDT
5/11/2009 05:34:02.6 UTC
Location: 40.099 N, 76.970 W Depth= 1 km
(40 deg 5.9 minutes North, 76 deg 58.2 minutes West)
Magnitude: Mc=1.2

Tuesday, May 12, 2009

Sichuan earthquake, one year later

(Photo and story from China Daily)

Top leaders joined millions of Chinese to mourn quake victims Tuesday afternoon on the one year anniversary of the massive earthquake in southwest Sichuan province.

President Hu Jintao and Vice Premier Li Keqiang attended a ceremony in the quake's epicenter Yingxiu Town, Wenchuan County.

All those attending the commemoration stood in a silent tribute to the victims of the earthquake, which left nearly 87,000 people dead or missing.

Ten floral baskets were put in front of a symbolic clock, with its hands stopped at 2:28 pm, May 12, 2008, the exact time when the 8.0-magnitude deadly tremor struck.

U.S. Geological Survey damage estimate:
  • At least 69,195 people killed, 374,177 injured and 18,392 missing and presumed dead.
  • More than 45.5 million people in 10 provinces and regions were affected.
  • At least 15 million people were evacuated from their homes.
  • More than 5 million were left homeless.
  • An estimated 5.36 million buildings collapsed.
  • More than 21 million buildings were damaged.
  • The total economic loss was estimated at 86 billion US dollars.

Saturday, May 9, 2009

Pennsylvania Disaster History

I was wondering the other day if Pennsylvania has a state equivalent of FEMA (Federal Emergency Management Agency). Yes, we do, and sure enough, it is PEMA (Pennsylvania Emergency Management Agency).

PEMA has a list of events comprising Pennsylvania Disaster History. Events are listed in chronological order, giving: date, general type of disaster, areas affected, and the response taken.

I re-classified the events somewhat, and came up with the following graph of the number of disasters, by type:
click on graph for larger version

Historically, earthquakes don't even make the list!

Based on this list, if you live in Pennsylvania, watch out for flooding and weather-related disasters, and fire. Of course, economic downturns are not listed.

Tuesday, May 5, 2009

USGS Awards $5 Million for Earthquake Research

RESTON, Va. - Five-million dollars in grants and cooperative agreements are being awarded in 2009 for earthquake research to 84 recipients including universities, state geological surveys and private firms, the U.S. Geological Survey (USGS) announced today. In addition, applications are being accepted for up to $7 million in grants and cooperative agreements for earthquake research in 2010.

"These grants underscore once again the importance to our nation of the earth science work accomplished by the USGS," Secretary of the Interior Ken Salazar said. "Earthquakes are one of the most costly natural hazards faced by the nation, posing a risk to 75 million Americans in 39 states."

USGS supports research on earthquake hazards in at-risk regions nationwide, including effects from earthquake shaking and the physical conditions and processes that cause earthquakes. The research is helping to better understand how earthquake hazards change with time and to reduce losses through effective earthquake forecasts based on the best possible scientific information.

"These research grants help the government gain access to talented academic, state, and private-sector researchers whose investigations are critical to helping prevent earthquake hazards from becoming disasters," said David Applegate, USGS Senior Science Advisor for Earthquake & Geologic Hazards.

The grants listed as pertaining to the Central and Eastern U.S are:

Pedro de Alba Central, University of New Hampshire
Use of Ground Failure Case Histories to Characterize a Design Earthquake for Coastal New England

Martin Chapman, Virginia Polytechnic and State University
Investigation into the Nature of Vertical Strong Ground-Motion for the Charleston, SC Area

Charles Langston, University of Memphis
Finding the Path Effect for Shear Waves in the Central US Using Broadband Waveform Inversion

David Dolenc, University of Minnesota Duluth
Effects of Shallow 3D Structure of the Mississippi Embayment on Ground-Motion Amplification: Collaborative Research between University of Minnesota Duluth and University of Memphis

William McCann
Estimating the Lower Limit of the Seismogenic Zone & Rates of Aseismic Slip on the Puerto Rico Megathrust Using Focal Mechanisms and Repeating Earthquakes

Jer-Ming Chiu, University of Memphis
High-Resolution P- and S- Wave Velocity Structure of the Post-Paleozoic Sediments in the Upper Missippi Embayment: Collaborative Research between the University of Kentucky and the University of Memphis

Youssef Hashash, University of Illinois
Site Amplification Factors for Deep Deposits & Their Application in Seismic Hazard Analysis for Central US

Stephen Horton, University of Memphis
Effects of Shallow 3D Structure of the Mississippi Embayment on Ground-Motion Amplification: Collaborative Research between University of Minnesota Duluth and

Edward Woolery, University of Kentucky
Ground Motion Site Effects in the Wabash Valley Region from the 18 April 2008 Mt. Carmel, Illinois Earthquake and Aftershocks

Robert Graves, URS Group, Inc.
Ground Motion Simulations for the 1811 and 1812 New Madrid Earthquakes

Edward Woolery and Zhenming Wang, University of Kentucky
High-Resolution P- and S- Wave Velocity Structure of the Post-Paleozoic Sediments in the Upper Mississippi Embayment: Collaborative Research between the University of Kentucky and the University of Memphis

Joe Gillman, Missouri Division of Geology and Land Survey
Detailed Surficial Materials Mapping for the O'Fallon 7.5 Minute Quadrangle as a Portion of the St. Louis Area Earthquake Hazards Mapping Project

Chris Cramer, University of Memphis
In Support of the St. Louis Area Earthquake Hazards Mapping Project: Update Hazard Map Uncertainty Analysis

John Puchakayala and Robert Smalley, University of Memphis
Constraining Central US Deformation Models with Continuous GPS Data

Randel Tom Cox, University of Memphis
Holocene Faulting and Liquefaction along the Southern Margin of the North American Craton (Alabama-Oklahoma Transform)

Stephen Horton, University of Memphis
The Effects of Radiation Pattern on Ground Motion in the New Madrid Seismic Zone
For a complete list of funded projects and reports, visit the Earthquake Hazards Program, External Research Support Web site.

The USGS is the applied earth science component of the four-agency National Earthquake Hazards Reduction Program (NEHRP), a congressionally established partnership to implement research and reduce losses from earthquake disasters.

Saturday, May 2, 2009

Jones Geological Services and Dillsburg

Jeri Jones of Jones Geological Services is often mentioned in media accounts of the Dillsburg earthquakes. His company's website has a piece on the Dillsburg series of small events on its web page, mostly focused on the activity last Fall. The isoseismal map contours values of Modified Mercalli intensity from the magnitude 2.1 earthquake of October 19, 2008.

Jones poses the following question:
What makes this swarm of shallow earthquakes interesting to investigate?
  1. The number of tremors felt over the last ten weeks
  2. The regular “boom” that accompanies many of these tremors
  3. A sulfur smell associated with the larger tremors and sometimes within the groundwater