Earth-Shaking Meeting

The scoop: Geoscientist Keith Knudsen chats with Larry O'Hanlon about the year's biggest meeting of seismologists and other very literally Earth-shaking matters. It's the annual Seismological Society of America meeting, which is held in Monterey, California this year . Besides looking at the local faults, the meeting covers a world worth of seismic science, including discoveries of powerful LiDAR imaging, a session on great earthquake ruptures, even some fun glimpses of what life is really like for the scientists who travel the world to study its interior.

larryo': Hello. You there?

kknudsen: Yes it looks like we've made this work - which organization do you represent?

larryo': I'm an online producer for Discovery Earth, a Discovery Channel website that specializes in Earth and environmental sciences (formerly a geologist and long-time freelance science writer)

kknudsen: OK, thanks I'm the Secretary of SSA, and a geologist who specializes in earthquake hazards.

larryo': Last year I managed to attend SSA, because it was right up the road from me here in New Mexico. Great meeting. Lots of neat stuff.

kknudsen: Yep, that was a good meeting - I'm a little California-centric, so I'm looking forward to this one too.

larryo': Monterey is a great place! Wish I could make it (as does my wife, who adores that town). Can you explain for my readers what SSA is and why there is an annual meeting?

kknudsen: SSA is the Seismological Society of America - learn more at www.seismosoc.org. It is a professional society of seismologists and other scientists and engineers (mainly) who research or study earthquakes and earthquake hazards. We have an annual meeting that usually attracts several hundred members of our society, from across the US and internationally. We also publish two journals, which are where a large fraction of recent earthquake-related research gets released.

larryo': Is it safe to say that SSA is truly international, rather than just American?

kknudsen: Yes, however I can't say off the top of my head how many members we have from outside the US. My guess would be a quarter or so of our members. I can get an actual percent if you like...

larryo': That's okay. Just asking because many of these sorts of orgs start out American and end up serving a much larger role. Any areas of seismology that are particularly hot this year at the meeting?

kknudsen: Since the meeting is taking place in Monterey, there will be a focus on Central California coastal seismology and tectonics. We are nearing the 20th anniversary of the 1989 Loma Prieta earthquake so there will be a session on how that earthquake advanced our understanding and our discipline many other topics as well.

larryo': Oh my. 20 years already. I had many friends in Santa Cruz during that event (I was, at the time, a recent grad of Earth Sciences there). The Hayward Fault -- that's a hot topic, is it not?

kknudsen: Here in the San Francisco Bay Area, there has been a lot of attention paid to the Hayward fault over the last year because we are 140 years from the last big earthquake to have struck the Hayward fault (in 1868). There isn't a session at the SSA annual meeting this year dedicated to the Hayward fault - that happened last year.

larryo': Ah.

kknudsen: There is a session at this year's meeting on last year's M 5.4 Mt Carmel Illinois earthquake, which happened during our meeting in New Mexico.

larryo': Oh yes. I remember. That made quite a stir.

kknudsen: Yes, many people don't realize that we do have earthquakes in the Central US. That M 5.4 was big enough that many people experienced it, yet it did not do a whole lot of damage. It was a good wake-up call though...

larryo': Yes. A sort of psychological quake in a way.

kknudsen: Yes, but we also learn a lot with every new earthquake - that is part of the reason I enjoy being in this field.

larryo': Are central US hazards getting more attention these days as a result? Or does the old conundrum apply: Folks lose interest and political will quickly.

kknudsen: I think there has been more attention on central and eastern US hazards since this earthquake. However, attention spans are pretty short. If you look at the history of earthquake related legislation you'll see that almost all of it happens in the year to 18 months following an earthquake.

larryo': So for hazards folks you go from being the center of attention to totally ignored in 12-18 months. Yikes. What sorts of things have been learned from Loma Prieta and Carmel, Illinois?

kknudsen: You'll have to come to the meeting to learn about the Mt. Carmel earthquake... I am looking forward to what people are going to present. That earthquake, I believe, was the best instrumented central/eastern event we've had. By this I mean that there were a lot of instruments (seismometers) that measured the earthquake. So we have learned a lot about how ground motions are transmitted in this part of the world. The aftershocks also tell us a lot about the nature of the fault that ruptured during the main shock.

larryo': Cool. Anything stand out in the abstracts -- since I'm never sure whether the media will cover it well.

kknudsen: The Loma Prieta earthquake caused a fair amount of legislation to be enacted (much of it designed to make us safer), and also taught us about San Francisco Bay area hazards. I'm not sure that I should point out a single abstract, there are many that look very interesting. Are you familiar with LiDAR? Its availability has really allowed us to learn a lot about the surface expression of active faults. I'm looking forward to the session on application of LiDAR.

larryo': That's the high-precision measurement of the land's surface?

kknudsen: Yes, it is a method to gather very precise measurements of the land surface; and it is particularly valuable in areas with vegetation because it can help us see the land surface through the trees.

larryo': So it helps you guys measure how tectonics or single quakes deform the crust at least in a vertical dimension. Right?

kknudsen: Yes, it also allows us to map faults with much greater detail. We can use these LiDAR data to identify sites where performing subsurface investigations will tell us about past earthquakes (Paleoseismology). We also use LiDAR to identify offset features in the landscape. If we can evaluate the age of these offset features, then we can calculate a fault slip rate - an important parameter when assessing hazards.

larryo': Will there be a lot of stuff derived from USArray data as well? That's halfway across the continent now, I think.

kknudsen: Yes, it is moving across the country every year. There is a session devoted to what we're learning from it. The new President of SSA will be chairing that session. He is a professor from New Mexico. Rick Aster from New Mexico Tech.

larryo': Any entirely new kinds of sessions this year?

kknudsen: There are sessions on Great Surface Ruptures - Earthquakes that have ruptured the surface for 100s of km. There is a session on Seismological field work: the good, bad and ugly, which may be very entertaining. Generally, most of what gets presented at our annual meetings is pretty new.

larryo': Ruptures are fun stuff. This is no doubt inspired from the Sumatra-Andaman event?

kknudsen: I just heard from our Executive Director; she believes that about 30% of our members are from outside the US.

larryo': That's a lot! The "A" in SSA is sort of showing its age.

kknudsen: The Great Ruptures that will be discussed are mainly ones that ruptured the surface on land. Some of them displace the land 5 m or more. Magnitudes are typically > M 7.9.

larryo': Alaska, 1964?

kknudsen: The 1964 (Good Friday) Alaska earthquake was a subduction zone earthquake that likely ruptured the ocean bottom. Among the earthquakes that are listed in the Great earthquake session description are: 1857 San Andreas in southern California, 1857 Wairarapa, New Zealand, 1906 in San Francisco Bay Region, 1920 in Mongolia, 1939 in Turkey, 1957 in Mongolia, 2001 in Tibet, Denali, Alaska in 2002, and most recently the 2008 Sichuan, China earthquake. I think the conveners of this session are interested in how the amount of slip during an earthquake varies along the fault. They are also interested in how surface measurements are different from those estimates of displacement that are derived from seismological and/or geophysical data.

larryo': Ah. So they help to test the theories. Help refine the physics?

kknudsen: Yes, there can discrepancies in results based on which discipline or approach is being used to derive answers. I'm one of the people that likes to be able to see and measure things at the surface of the earth (I'm a dirt guy). Others like to reveal processes based on seismological or geophysical data. The best scientists are those that make use of multiple lines of reasoning...

larryo': And you have so much to study, either way! Mountains of data (forgive the pun). Pretty exciting work.

kknudsen: Yes, I really enjoy it. I think partly because it is a relatively young discipline and when you get right down to it, we have a lot to learn. I think I better sign off pretty soon.

larryo': I was about to let you go. Thanks for your time. I really appreciate it. I'll be looking for news stories or press releases from the meeting and pointing readers towards them. Have a great meeting!

kknudsen: OK, please send me the link to where I can see your stories.

larryo': Will do. I'll have several items up during the week. Videos, a slide show of the Good Friday event, etc. Will let you know.

kknudsen: And feel free to contact me in the future with questions/comments - bye

Article posted April 8, 2009.