Thursday, April 30, 2009

Yes, Dillsburg, PA, you just felt another one

LCSN Earthquake Alert

Lamont-Doherty Earth Observatory (4/30/2009 22:16 EDT)

Origin time: 4/30/2009 18:36:11.3 EDT
4/30/2009 22:36:11.3 UTC

Location: 40.073 N, 77.013 W Depth= 1 km
(40 deg 4.4 minutes North, 77 deg 0.8 minutes West)

Magnitude: Mc=2.0

On Thursday evening, April 30, 2009 at 18h 36m 11s EDT,
a minor earthquake of magnitude 2.0 occurred near Dillsburg,
Pennsylvania (25 km southwest of Harrisburg, Pennsylvania).

There are felt reports from Dillsburg and Franklintown.

Pennsylvania's largest earthquake this week

is now a

Arlen has long been pretty moderate for a Republican. But at 79, isn't it about time he retires to "spend more time with his family," as they say?

Wednesday, April 29, 2009

Six months of south-central Pennsylvania seismicity

The figure and the list below are from the LCSN:

    Date        Time      Lat     Long   Depth Magnitude
year-mo-dy hh:mm:sec (N) (W) (km) (Mc)
Lancaster County, PA
1972-12-08 03:00:32.5 40.150 76.220 4 0.0
1978-07-16 06:39:39.6 39.900 76.220 0 0.0
1984-04-19 04:54:55.1 39.946 76.323 7 2.9
1984-04-23 01:36:02.0 39.946 76.323 4 4.1
1984-04-23 02:46:00.5 39.946 76.323 10 2.5
1994-01-16 03:03:31.3 40.532 76.247 4 2.0
1995-03-11 21:10:16.0 40.100 76.400 5 2.7
1997-11-14 03:44:11.7 40.164 76.276 6 3.0
2000-03-22 20:48:00.0 40.070 76.300 1 1.8
2000-10-05 23:33:59.0 40.080 76.300 7 2.0
2001-07-17 14:41:20.2 39.937 76.340 1 1.8
2008-12-27 05:04:34.5 40.114 76.403 3 3.4

Adams County, PA
1994-05-26 17:21:58.2 39.950 77.187 11 2.8

Dillsburg, York County, PA

1997-06-16 05:43:16.6 40.098 76.967 5 1.9

2008 (21 events)
2008-10-05 22:36:48.1 40.054 76.967 2 2.0
2008-10-06 01:06:13.4 40.120 77.025 0 1.2
2008-10-06 06:15:38.4 40.069 76.992 0 1.1
2008-10-19 08:21:22.7 40.080 77.019 5 1.9
2008-10-19 08:22:07.3 40.078 76.963 5 2.1
2008-10-19 08:26:20.5 40.168 77.038 5 1.2
2008-10-19 08:28:09.0 40.087 76.998 5 1.5
2008-10-19 08:58:31.7 40.092 76.974 3 1.8
2008-10-19 09:06:01.5 40.091 77.018 5 1.0
2008-10-19 09:08:20.7 40.056 76.962 5 0.8
2008-10-19 09:08:44.3 40.092 76.987 5 1.1
2008-10-19 09:17:34.8 40.100 77.009 5 1.7
2008-10-19 09:49:19.1 40.095 77.002 5 1.0
2008-10-19 09:49:51.7 40.075 76.973 5 1.5
2008-10-19 09:50:11.4 40.091 76.989 5 1.6
2008-10-20 00:08:26.6 40.159 77.107 5 1.2
2008-10-20 00:14:03.9 40.075 77.005 5 1.1
2008-10-20 02:16:02.4 40.090 76.984 5 1.5
2008-10-23 15:55:32.3 40.068 76.962 5 1.2
2008-11-07 04:07:03.0 40.096 77.006 1 1.4
2008-12-31 05:34:08.8 40.107 77.003 1 2.1

2009 (3 events)
2009-04-22 13:21:14.1 40.073 77.002 1 1.1
2009-04-23 22:26:04.4 40.085 76.998 1 2.4
2009-04-24 05:36:48.8 40.064 77.026 1 2.9
See any patterns here? Maybe I'll try that next.

Tuesday, April 28, 2009

Holiday quake hypothesis - Earth Day in Dillsburg


You may remember my hypothesis that earthquakes tend to occur on holidays. If not, it doesn't matter, because I'm just kidding. But, from the York Daily Record:

Dillsburg marks Earth Day with another earthquake
Daily Record/Sunday News
Updated: 04/23/2009 12:38:30 AM EDT

An earthquake that registered 1.1 on the Richter Scale shook the Dillsburg area about 9:21 a.m. Wednesday, according to the U.S. Geological Survey.

"Boy, did we have one this morning," Carroll Township resident Michael McCaffrey said.

He was taking a shower and heard a thunderous boom. He thought that his wife, Kathleen, who recently had surgery, might have fallen out of bed. He ran to check on her, and she was fine.

The couple figured it was another earthquake.

"It makes you wonder when they're going to stop - probably never at this point," he said.

The seismic activity in the Dillsburg area - several earthquakes and nearly 460 tremors since Oct. 3 - had seemed to be dwindling in recent months.

The last measurable earthquake shook the area New Year's Eve.

Residents reported booms during the weekend, preceding Wednesday's earthquake, said Jeri Jones of Jones Geological Services.

Jones said he has noticed that the rumblings, which were occurring during the night, are now happening more during the day.

He'll be meeting with township supervisors next month to discuss placing portable seismographs in the area.

Scientists with the Lamont-Doherty Earth Observatory of Columbia University placed portable seismographs in the area last fall to record the tremors and analyze the data.

Senior research scientist Won-Young Kim said in an e-mail Monday that their work is still going on, and he hopes to finalize it in the next couple of weeks.


An earthquake that shook the Dillsburg area Wednesday morning is the 19th one that has been measurable since the fall, said Jeri Jones of Jones Geological Services.

The earthquake at 9:21 a.m. Wednesday measured 1.1 on the Richter Scale.

Three earthquakes measuring 2.0 or greater on the Richter scale have hit the Dillsburg area since the fall. Nearly 460 tremors have been reported in the area since Oct. 3.

Monday, April 27, 2009

Latest Dillsburg quakes - LCSN at the ready

A seismology team from Columbia University set up portable seismographs in the area. Retired Millersville University professor emeritus of geology Charles Scharnberger holds a map showing earthquake intensity zones. Zone III in center is the most intense with decreasing intensity outside the zone (photo credit: ).


Friday April 24, 2009, 10:28 AM

2 earthquakes reported in Dillsburg area
by LARA BRENCKLE, Of The Patriot-News

A 2.9-magnitude earthquake rattled residents around the Franklintown, Pa., area early this morning, setting off concerns that the series of temblors that rocked northern York County in the fall and early winter have returned. The U.S. Geological Survey reported today's quake occurred at 1:36 a.m.

On Thursday, residents of Dillsburg also experienced tremors, with a 2.4 magnitude quake startling residents there. Dillsburg Borough manager Karen Deibler was in her office when Thursday's quake struck.

"I don't think a lot of people knew what was going on last night because it's been such a long time (since we've had one)," Deibler said.

The last spate of earthquakes occurred from October to January.

It's been quiet, however, and Deibler said people figured they were over. "Nobody really knows what to think at this point," she said.

Sunday, April 26, 2009

New quakes in Harrisburg, Pennsylvania, area

There have been three small earthquakes in the Harrisburg area in the last few days. I'm returning tonight from the Society for American Archaeology meeting in Atlanta, flying into Harrisburg. Maybe I'll get to feel one?

I like the way the above graphic present four dimensions of information - latitude, longitude, earthquake magnitude, earthquake time - on a two dimensional map.

Update time = Sun Apr 26 12:19:15 EDT 2009
Here are the earthquakes appearing on this map, most recent at top ...

y/m/d h:m:s deg deg km

2.9  2009/04/24 01:36:48 40.064N 77.026W  1.5   23 km (14 mi) SW  of Harrisburg,PA
2.4 2009/04/23 18:26:04 40.085N 76.998W 1.0 20 km (12 mi) SW of Harrisburg,PA
1.1 2009/04/22 09:21:14 40.073N 77.002W 1.0 21 km (13 mi) SW of Harrisburg,PA
2.1 2008/12/31 00:34:08 40.107N 77.003W 1.0 18 km (11 mi) SW of Harrisburg,PA
3.4 2008/12/27 00:04:34 40.114N 76.403W 4.0 9 km ( 6 mi) W of Lancaster,PA
1.4 2008/11/06 23:07:03 40.096N 77.006W 1.0 19 km (12 mi) SW of Harrisburg,PA

Figure and data from Lamont-Doherty Cooperative Seismograph Network.

Wednesday, April 22, 2009

Happy Earth Day, 2009

from NASA

Today is the 39th anniversary of the first Earth Day, which I remember from when I was an undergraduate.

May we continue to use the Earth's burps to learn more about our planet, and minimize the dangers posed to our fellow inhabitants.

Monday, April 20, 2009

Recovery Act Funds to upgrade seismic networks

Date: April 15, 2009
Contact: Joan Moody
(202) 208-6416

U.S. Department of the Interior
News Release
SAN FRANCISCO, CA – Secretary of the Interior Ken Salazar today announced the U.S. Geological Survey will fund $29.4 million in earthquake network upgrades nationwide through the American Recovery and Reinvestment Act of 2009, an investment that will significantly improve the timely delivery of information to high-hazard regions such as the Bay area.
Eat your heart out, Bobby Jindal (see earlier post).

USGS will replace old instruments – some of which have not been upgraded in 40 years – with state-of-the-art, robust systems across the highest earthquake hazard areas in California, the Pacific Northwest, Alaska, the Intermountain West, and the Central and Eastern United States.

“The timely delivery of earthquake information can mean the difference between life and death,” Salazar noted. “It requires critical infrastructure such as modern seismic networks and data processing centers so scientists can provide emergency responders with information to save lives and reduce economic losses. With nearly 75 million Americans living within earthquake prone areas, this investment is long overdue.”

Statewide, California has more than a 99 percent chance of having a magnitude 6.7 or larger earthquake within the next 30 years, according to scientists using a new model to determine the probability of big quakes. In the Bay area specifically, there is a nearly 2 out of 3 chance of an earthquake of that magnitude in that time period.

Secretary Salazar said that a significant portion of these funds can be expected to go to the state because of the high level of earthquake risk in California, the substantial existing partnerships that the USGS has with universities and the state, and the location of some of the major seismic equipment manufacturers in the state.

The funds will be used to:

  • upgrade the seismic and geodetic stations that monitor earthquakes;
  • improve communication systems to make them more robust and reliable;
  • lay the groundwork to enable earthquake early warning – The latter is a technology in operation in Japan, Taiwan and Mexico that uses sensor detections at the earthquake epicenter to broadcast warnings to nearby areas about to be shaken;
  • support students at universities in California who will be involved in the installation, providing a unique educational experience and helping to train the next generation of earthquake scientists;
  • help save jobs that are threatened by cuts in state funding in California.

The USGS earthquake monitoring funds are some of the first Department of the Interior projects under the Recovery Act. Overall, the Department of the Interior and its agencies will manage $3.0 billion in investments as part of the recovery plan signed by the President to jumpstart our economy, create or save jobs, and put a down payment on addressing long-neglected challenges so our country can thrive in the 21st Century.

Eat your heart out, Bobby Jindal.

Wednesday, April 15, 2009

Satellite interferogram of L'Aquila earthquake

Click above for larger image

Studying satellite radar data from ESA's Envisat and the Italian Space Agency's COSMO-SkyMed, scientists have begun analysing the movement of Earth during and after the 6.3 earthquake that shook the medieval town of L'Aquila in central Italy on 6 April 2009.

Scientists are studying Synthetic Aperture Radar (SAR) data from these satellites to map surface deformations after the earthquake and the numerous aftershocks that have followed. SAR Interferometry involves combining two or more radar images of the same ground location in such a way that very precise measurements – down to a scale of a few millimetres – can be made of any ground motion taking place between image acquisitions.

The InSAR technique merges data acquired before and after the earthquake to generate 'interferogram' images that appear as rainbow-coloured interference patterns. A complete set of coloured bands, called 'fringes', represents ground movement relative to the spacecraft. The interferogram shows nine fringes surrounding a maximum displacement area located midway between L'Aquila and Fossa, where the ground moved as much as 25 cm (along a line between the satellite's orbital position and the earthquake area).

To ensure all scientists are able to contribute to the analysis of the earthquake, ESA is making its Earth observation dataset collected over the L'Aquila area freely accessible with an innovative fast data download mechanism. The dataset will be continuously updated with the newest Envisat acquisitions.

Text from AAAS EurekAlerts.

Figure from European Space Agency, from where more data are available.

Saturday, April 11, 2009

My only earthquake, 25 years ago on Easter

I experienced my only earthquake on Easter Sunday, 23 April 1984. I had been in Lancaster, PA, for a year, my 1-year old son was sleeping upstairs, my wife and I were sitting in the kitchen. All of a sudden we heard a low rumble, and then kind of a boom. My wife thought maybe there had been a truck accident, or an explosion in our boiler, both common reactions to eastern earthquakes. Geophysicist that I am, I realized immediately it was an earthquake (perhaps assisted by the fact that a foreshock had occurred during the previous week). This was the best kind of earthquake – exciting, a little cracked plaster, some data for seismologists to play with, but no one hurt, almost no damage. Reports from F&M said that during the showing of the weekend movie (before the days of DVDs), people had panicked and run outdoors. This would make it intensity V on the Modified Mercalli Scale.

The cooperation that event fostered between seismologists at Millersville University and Columbia University was important in the development of the group that led to this blog.

Now my two sons are grown up, and living in the San Francisco Bay area. I hope they don't experience anything worse than a magnitude 4 earthquake.

Tuesday, April 7, 2009

Un terremoto orribile in Italia

You've probably heard about the magnitude 6 earthquake in Italy, with the impact still being tallied.

If you can read Italian (I can, somewhat), you can look at the account and data provided by the Italian National Institute of Geophysics and Volcanology, source of the map above.

Photos are available from the BBC.

The Berkeley Seismo Blog linked to on the left also has an account of the tectonic setting.

Here's the record of the waves from the Franklin & Marshall College seismograph:

Thursday, April 2, 2009

Rock and roll - falling rocks in Yosemite

This and other photos from the 2006 Yosemite rockfall at

Gravity sucks, and Yosemite National Park has some steep slopes, so the result is rockfall. Mass wasting. Downslope movement. Check out some video of a 2006 rockfall at Yosemite.

The Seismo Blog has a really nice piece on a rockfall in Yosemite Saturday morning, and quotes Greg Stock, the park geologist: the rocks "fell roughly 1800 feet to the floor of Tenaya Canyon, striking ledges along the way. Debris extended well out into the Canyon, knocking down hundreds of trees and burying the southern portion of the Mirror Lake loop trail... Fortunately, due to the event occurring in the early morning, there were no injuries."

Seismo Blog addresses what happens when tons of granite come crashing down to the valley floor. The impact makes the ground vibrate and creates seismic waves very similar to the ones radiated by an earthquake. Seismic stations all over Northern California and Nevada - as far away as 250 miles from Yosemite - registered these waves. The rockfall had the same energy as a magnitude 2.4 earthquake.

Click above for larger image
The seismic waves of Saturday's rock fall were recorded by many earthquake stations. The 33 depicted here are sorted top to bottom by increasing distance from Yosemite. It takes seismic waves longer to travel further distances, hence the "delay" of almost 60 seconds between the arrivals of the waves at the nearest and most distant stations. (from Seismo Blog)

This probably make more sense than talking about the equivalent Richter magnitude of the Chernobyl nuclear power plant accident!