Thursday, November 27, 2008

Earthquake relief during this holiday season

The last five years have seen some of the most damaging earthquakes in history: China, Pakistan, Sumatra.
Beichuan, China, 2008

In this season of American Thanksgiving and year-end holidays, some of us interested in the field of seismology and earthquakes might wonder how we could aid some of the victims of these not-so-long-ago disasters.

There are many excellent relief agencies out there (although perhaps some not so efficient as others). There are groups which independently audit charitable agencies, and one that I came across online is the American Institute of Philanthropy. This group suggests that especially worthwhile agencies for Chinese earthquake relief are:

Other agencies that might be worth considering include:

Tuesday, November 25, 2008

What's shaking?

This cartoon is posted on the Franklin & Marshall seismograph display:

In the old days of a drum recorder, we often lost data when we forgot to change the paper. Now that the recording is digital, we are doing better. And we have evidence for that. Mitch, maybe you can explain those QUACK statistics?

Saturday, November 22, 2008

Weird seismic phases

When we cover introductory seismology, we learn about P, S and maybe L waves. But the travel time curves a couple of blogs down show many more "phases," with acronyms like PKIKP. Yikes, what is that letter salad all about? Well, the letters indicate where the seismic wave has traveled in the Earth, and whether it has traveled as a P or an S wave, or an L wave if on the surface. The trick is that as waves are reflected from interfaces, like the boundary between the Earth's mantle and core, or when they are bent (refracted) as they cross these boundaries, P waves can convert to S waves and vice versa.

So, we can get phases like those shown below:

These figures are from the text An Introduction to Seismology, Earthquakes, and Earth Structure, by Seth Stein and Michael Wysession, Blackwell Publishing, 2003. (I just discovered this online resource - it's great.)

To translate what the letter sequences mean, there is a full listing of seismic phases agreed upon by IASPEI, the International Association of Seismology and Physics of the Earth's Interior.

C U soon!

Monday, November 17, 2008

The Great Southern California Shakeout!

At 1 p.m. (10 a.m. Pacific), the Museum of the Earth in Ithaca, NY, participated in the Great Southern California Shakeout! The museum is a member of the Lamont-Doherty Cooperative Seismographic Network, and we have earthquake activity as its seen from our seismographs on display for the public!

As a part of our outreach mission, we participated in the shakeout. Here's the story...

We have 26 staff at the museum, along with classroom visitors and general public walking through our doors every day. On the day before the Shakeout, all of the staff got together to learn why we were participating. Te Great Southern California Shakeout was an earthquake preparedness drill, similar to a fire drill, etc. So, it was practice. But it was educated practice. The USGS (United States Geological Survey) actually calculated the possible strength of the next 'big earthquake' to hit the California region, and where it would occur along the San Andreas fault system. Based on that information, staged drills involving hospitals, medical centers, and other rescue workers, occurred throughout the week.

Also, all participating individuals and companies, like the Museum of the Earth, agreed to do a drill at the same time on Nov. 13th at 10 am Pacific. So, at 1 p.m. here on the East Coast, an announcement came across our PA system telling us that an earthquake was occurring. We had been instructed to "Drop, Cover, and Hold On." In the building I was in, we all climbed under our desks to hide from falling books, computers, and other dangerous objects. In the museum itself, guests were asked to find cover under our display cases where available, or just duck down and cover their heads to protect themselves.

I think it was a neat experience! The idea of having our museum guests participate to help educate the public is really what we're all about at the Museum of the Earth, and it was certainly a hands on experience for everyone.

Some highlighted information to take home:
1) The majority of people who die during an earthquake do so not because of collapsing buildings, but from trauma to the head (from, say, a huge textbook falling on our heads). That's why they suggest that you Drop, Cover, and Hold On. Dropping and covering protect your head, and holding on to a large piece of furniture keeps you in the same place relative to the large furniture.

2) Finding a doorframe to protect yourself under is not the safest thing to do. You may not be able to walk once the earthquake starts, so the best thing to do is drop where you are.

3) If you climb under your desk, you're bound to find dustbunnies!

Cheers from the Museum!!!

Sunday, November 16, 2008

Two out of three ain't good

Will we be more ready for the next big earthquake in California then we were for 9/11 or Hurricane Katrina?

"U.S. Geological Survey seismologist Lucy Jones remembers attending an emergency training session in August 2001 with the Federal Emergency Management Agency that discussed the three most likely catastrophes to strike the United States.

First on the list was a terrorist attack in New York. Second was a super-strength hurricane hitting New Orleans. Third was a major earthquake on the San Andreas fault.

Now that the first two have come to pass, she and other earthquake experts are using the devastating aftermath of Hurricane Katrina as an opportunity to reassess how California would handle a major temblor." (Los Angeles Times, 9/8/05)

This past week southern Californians participated in a huge planning simulation,

The Great Southern California ShakeOut

I think we'll be hearing from one of our contributors about this exercise.

Saturday, November 15, 2008

Interpreting seismograms with travel time curves

The travel time curve below looks much more complicated than the ones seen in introductory text books. We'll need to spend a couple of blogs explaining that. But notice the repetition of the letters P and S. These are the two physically different types of body waves that you're probably familiar with, the push-pull P-waves and the shear S-waves. The third different physical type of waves are the surface waves, often designated with the letter L. The way that the P's and S's are combined (PP, PcS, PKP, etc.) indicate the path that these waves take through the body of the Earth. All of this is plotted against the great circle angular distance between where the earthquake occurred to where it is observed. I'll show you how to calculate those angles later, but for now, accept that the distance from the earthquake in Pakistan to the seismograph at Lamont in New York is 100°. Note that for this distance, the travel time for the P wave is 14 minutes, and the travel time for the PP curve is 18 minutes.


Now look at the Lamont seismogram below. It looks to me like the first real small blip of energy that we can detect with the naked eye is at 11:51. I'm not talking abut the larger waves that arrive later, but that first small sinusoidal pulse of energy. This blip of energy is 18 minutes after the quake occurred, and at this distance from the quake, would seem to the the so-called PP phase. What is PP (no scatological humor, please)? Stay tuned.

Sunday, November 9, 2008

Dillsburg earthquake swarm

Here is an update on the continuing seismic activity near the borough of Dillsburg, in northern York County, PA. The swarm began on Friday, October 3, and has continued until at least Saturday, November 8. Residents of Carroll Township, just southeast of Dillsburg, report hearing and feeling many "bumps" that resemble explosions. Sometimes these occur in clusters and sometimes singly. At least 100 of these small earthquakes have been reported since the swarm began. Some have been large enough to be detected by stations in the LCSN. The largest recorded so far occurred early Sunday morning, October 19. It had a coda magnitude of 2.1. (Coda magnitude is calculated by measuring the duration of the decaying signal following the initial impulse, and applying an empirically determined formula that is different for different regions.) A local network of four temporary stations has been deployed around the area where the earthquakes are being felt. Records from these stations should provide highly accurate times and locations for these events. The fact that these very small earthquakes are being felt so distinctly by local residents implies that they are originating at a very shallow depth.

Similar swarms of small earthquakes have occurred in other locations in the Northeast, notably in Columbia, Maryland, in 1993, and Moodus, Connecticut, in the 1980s (and going back to colonial times.) The Moodus swarm was investigated by John Ebel of Boston College (Seismological Research Letters, vol. 60, No. 4, Oct.-Dec., 1989, pp. 177-184). The hypocenters were found to range in depth from 0.4 to 2.4 km., but could not be associated with any obvious fault or other geologic structure. The focal mechanism was found to be reverse faulting with the axis of maximum compressive stress oriented WNW-ESE. Moodus, like Dillsburg, is located in a Mesozoic basin where Triassic age sedminetary rocks have been intruded by diabase.

About 200 local residents attended a public meeting at the Carroll Township building on October 28. Some were fearful that this swarm of small earthquakes may be a precursor to a large, damaging quake. In the light of experience with similar swarms elsewhere, this seems highly unlikely. In all probability, the swarm will continue for a few more weeks or months, and then stop as mysteriously as it began.

Saturday, November 8, 2008

Interpreting the Pakistan earthquake seismogram

I'll try to work through this one step at a time, in order to allow our many readers to catch up.

Let's consider when waves from the recent Pakistan earthquake should have arrived at the Lamont-Doherty seismograph, and compare that to when they actually did.

The NEIC information says that this quake (the second of two similarly sized events) occurred at Oct. 29 at 11:32:43 UTC (coordinated universal time).

Let's solve this today by using the theoretical P-wave arrival times tabulated and graphed by the NEIC. According to the table, the P (diffracted wave) should arrive in New York at 11:46:30, 14 minutes after the earthquake occurred.

Look at the seismogram below. There seems to be a small blip of energy at about 11:51, 18minutes and 20 seconds after the earthquake occurred.

Is this the wave arrival referred to above? Why is this blip so small compared to what follows? Can we get a more detailed look at this seismogram? How is this approach related to the use of travel-time curves? And what is Pdiffracted anyway?

You'll have to come back for that.

Saturday, November 1, 2008

NEIC - Your best source of earthquake information

If you hear about an earthquake on the news, where can you go for more information? I assume people would search their favorite journalistic source - Google, Yahoo, New York Times, BBC, Reuters, NPR - for the newsy stuff. But what about the basic science of the event?

I'd suggest for large teleseismic (see NEIC glossary) quakes that you visit the U.S. Geological Survey Earthquake Hazards Program/National Earthquake Information Center, at .

Each significant event has its own listing, including the Pakistan quake.

For the geographically faint-of-heart, you can get a general global location:

globe showing location of 10-degree map

You can look at historic earthquake patterns in the area (seismicity), and the relationships to plate boundaries:

Historic Seismicity

Magnitude / Depth Legend

You can read about the geology and tectonic environment that are related to this event:
Earthquakes and active faults in western and northern Pakistan and adjacent parts of Afghanistan are the result of the India plate moving northward at a rate of about 40 mm/yr (1.6 inches/yr) and colliding with the Eurasia plate. Along the northern edge of the Indian subcontinent, the India plate is subducting beneath the Eurasia plate, causing uplift that produces the highest mountain peaks in the world, including the Himalayan, the Karakoram, the Pamir and the Hindu Kush ranges. West and south of the Himalayan front, the relative motion between the two plates is oblique, which results in strike-slip, reverse-slip, and oblique-slip earthquakes. The pattern of elastic waves that were radiated by the October 28 and 29, 2008, earthquakes implies that each earthquake was the result of predominantly strike-slip faulting. Seismographically recorded waveforms imply that the shocks were caused by either left-lateral slip on a northeast-striking fault or right-lateral slip on a northwest-striking fault.
For this major event, you can even download a poster suitable for display.

And, in what will become useful for a subsequent lesson on interpreting seismograms, you can find out how long it should have taken the P-waves from this earthquake to reach any point on Earth:

(click above for more detail)

You can be sure that we'll return to the NEIC web site in the future.