Sci-Q: San Diego Scientists Answer Questions About Earthquakes

This is KBPS midday edition. I am Maureen Cavanaugh. Earthquakes are nothing new to Californians nearly 2100 quakes shook Southern California last year. The latest quake was a 3.8 recorded 44 miles off shore of Imperial Beach last night. What do we really know about earthquakes? Was the latest research about earthquakes and climate change? On this edition of our science series, Sci-Q, will discuss some of the latest research to dispel some myths and take your questions. The number here is 888895 The number here is 888-895-5727 for your earthquake questions. Joining me are Kim Bak Olsen, professor, geological sciences, San Diego State University and Pat Abbott, professor emeritus, geology, San Diego State University . We talk a lot about faultlines when we are discussing earthquakes. Could you tell us what they are and white earthquakes happen along faultlines? >> Lancer fractures in the earth were stress has built up and there's already a fracture or weakness playing there, once I can move past the other. That movement, we feel the energy released in What's the most seismically active fault in San Diego County? >> If we could extended to Imperial County, the one that has done the most large earthquakes we the San Jacinto fault. What about the Rose Canyon fault? The That has been very quiet which doesn't want to low you into sleep but they operate on different timescales than we live on. We earthquakes measure is pretty competent a. Can you attempt to certify There are several ways earthquakes can be measured. The most popular method is the Richter method. Those introduced by Charles Richter in the 1930s. Is the local scale that depends on the amplitude of the shaking in a certain site where it's measure. It's a logarithmic scale that means magnitude 6 is 10 times larger in amplitude and a magnitude 5 . It's 30 times bigger in terms of energy. >> Since this scale tends to saturate in larger magnitude, the amplitude of the waves don't keep increasing beyond magnitude 7 or eight. That scale doesn't really work well for those earthquakes. Is another scale called the moment magnitude scale which relates the size of the alts in the area and the amount of slippage and it's more disagree correct for the large earthquakes. >> Are both of them used? Yes. One thing about the Richter scale is its almost immediate. Right away when an earthquake occurs, your what's the epicenter and with the That's not as accurate as the others. We do for general consumption is Kim makes those calculations and you convert it to what would be an equivalent Richter number because the public are used to those. When we have a magnitude 9, that is something people can relate to better. >> Viewer audience members want to know about the risk of tsunami here? This question is from the public. Was the likelihood of a near offshore earthquake causing a catastrophic tsunami or tidal wave which floods the Southern California area? >> This is one of the events that has a lot of scientific basis behind it but is a low-frequency events. We used to say San Diego area was protected from tsunami by all the offshore islands and that a sick great natural barrier to take that Japanese earthquake and reduce it to only a 1 foot high wave coming into San Diego. However, in Papua New Guinea, they had an offshore earthquake in 1998 set loose sand slide that pushed three major tsunami waves across the barrier bar in the picture looks just like mission beach or the Silver Strand and that killed 2200 people and so now we realize we have that. Those offshore islands are there because they are uplifted by false there probably not big enough to to generate a significant tsunami but a landslide our submarine sand slide can. That's why we have the signage is around the coastal areas to educate people to be aware of the possibility. >> How important is the geology under or near your home in terms of the severity of earthquake damage? How do you find out about the geology under your property? It can be very important. Different soils react very differently to the shaking from an earthquake. It's a very clay rich soil , you might have what's called liquefaction with a soil turns into a liquid. That can generate very strong damage to building structures. Any local specific defects like that, the proximity to a bluff, or gravity is working to pull the bluff into the ocean is a very important factor. Any information you can get about what the conditions are could be very helpful. You can get that information from the city of San Diego and so on. You can find out what the specific geology is in areas. Can you see what panties are more prone to liquefaction? >> For Iraq to liquefy means well. That means it has to be loose to begin with. Let's mentally take a trip around mission Bay. There's all those sands with water in them and how we can want to San Diego River with all the mission Valley shopping centers. Loose sand you can pick up with your fingers. If we have a high water table has a lot of rain, than those loose water saturated sands are all the more prone to flow in arms the buildings are designed as a ships, they are supposed to stay place on ground. >> I have a question from a listener about any kind of relation between El Niño and earthquakes. I would imagine that could broaden out to the IDM of climate change and earthquakes? What do we know but that? That's a timely question with the climate change going on. It's generally been expected that anything that goes on the surface of the earth is too far away from where the US could actually get generated about 5 to 10 miles below the surface. Whether atmospheric pressure, water levels and someone wouldn't have much effect on generating earthquakes. However, there's been a recent science that point otherwise. Namely from the salt and see area. Which the salt and see didn't always used to be the current site. East be more than 1 1/2 times Lake Tahoe and there have been plenty of flooding events that Lake and that has been a correlation down between these huge flooding events in and out of the lake in large magnitude 7 earthquakes so there seems to be some correlation that what happens in terms of water fluctuations can actually affect an trigger earthquakes. >> We've a question from a caller who is also about the salt and see . At the construction of thermal power plants, they are near faultlines, could the construction trigger earthquakes that we could deal in San Diego County and that question is from Simon. >> I think they'll be very unlikely to happen. The construction of a power plant is very localized . The weight and pressure from that is likely going to be so small that it won't happen. On the other hand, I would mention the San Andreas Fault which is located right along the salt and see in going northward from there, is expected to be very ready to go. Is compared with a 15 month pregnant woman, a go anytime. Having said that, we don't expect very much needed in terms of pressures to set up another earthquake on the San Andreas Fault. It's been more than 300 years since the last big event on the San Andreas. On average these large earthquakes happen every 130 years. >> Here is another question, she asks what is the history of earthquakes in San Diego County? >> In San Diego County, we don't have much of a history. When I say that, I'm going back to 1769, the founding of the nation. We haven't had a really large earthquake occur within the city or even the county. Just to the east, we have Elsinore falls, San Jacinto, San Andreas. We have offshore ones as well. Within San Diego County, the Rose Canyon fault. The northern and moved up in Long Beach in 1933. Second deadliest earthquake in California history, but the Rose Canyon fault , that has not moved in historic time, the last 230 or so years. >> Do we know with the longest earthquake has been? Does the thing that really creates the damage we see. Is met with an earthquake is of a long duration is profound for a long time . Yes. We can use the word long in two different ways. The longer the fault, -- a jacket with a zipper is a better illustration of a fault. We talk about a long time, I'm relating that's a long rupture length, it's like a zipper. The whole fault is not moving at once, it's a movement that moves along the fault. The longer shaking, the more damage. >> A very potent example that worked out well for us, faults can rupture from north to south or south to north or start of the middle and go both ways. 1989, started in the middle and ruptured simultaneously. To get the most horrific image has to be the collapse of the 880 freeway in Oakland. With the same thing in San Francisco called the Embarcadero roadway. It was an engineering failure but it didn't collapse and kill people go had a ruptured from south to north, that would have come down and we would of had some more horrific pictures of people crushed with From that serious and tragic image, I'm going to a couple of myths about earthquakes and ask you what you think of them. Lots of people seem to think animal behavior changes before an earthquake. Is that you animal behavior changes several hours or days prior to an earthquake? >> That has been some indicators that animals, in particular dogs, can behave erratically. Typically, I think seconds before a major earthquake. If you want -- second -- Seconds before? >> Yes. What has been related to the physical reason for that's could be these dogs feel the first waves that travel through the area also called the P wave such are typically not the largest amplitude ways. People might not feel the first arriving wave but once those surface waves arrive, typically seconds later, that is what is imagined as the big earthquake shaking happening. That's what people feel but they didn't feel the little indicator that came first which We have another caller. Originally from Nepal he was to ask a question about the last earthquake in the Paul. He says the energy the last earthquake has not completely released, what do we know about the outline that caused that quake in the timeframe when energy from the quake could be released again? >> This goes to plate tectonics. Why do we have the whole uplift in Tibetan plateau. Tens of millions of years now, India has moved northward, has pushed into Asia and continues to push their. This is one of the areas of the world we have the greatest earthquakes of all. If you think back to the last 15 years or so, there's that Chinese earthquake in 2008. Is one of Pakistan a few years before that. When you say, does all the energy release on the fault? No. You're talking about lifting up Mount Everest and all those mountains, you're looking at whole Tibetan plateau. These are basically cotton and wide faults and no one earthquake is going to come close to releasing all the stress. Will there be a next big one on that line? In a way, I like to go beyond hotlines and visualize India as a bulldozer burning into Asia. As a bulldozer compost things up in a weird pattern, things can break loose and all kinds of places. I wish we had more time. It's very interesting. I've been speaking to Kim Bak Olsen, professor, geological sciences, San Diego State University and Pat Abbott, professor emeritus, geology, San Diego State Thank you. >> Remember to watch KPBS evening edition on KPBS television. Today at five and 6:30 PM. Treatise again tomorrow on KPBS midday edition right here on KPBS FM. I am Maureen Cavanaugh, thank you for listening.