![]() "I would be lying if I was to tell you I had all the answers to this. "The important thing is that it is wildly different depending on where you are," West said. One of the surprises from the raw data is the extreme variation and complexity of Anchorage's response to earthquakes. ![]() That information could determine building design standards in closely defined zones.Ī lot of work will come between now and then. With extensive study, the data could also allow scientists to designate soils in different areas around town according to how they accelerate seismic shaking. Yang said the information will help validate models that engineers use to design buildings in earthquake country. "This map is basically presenting our firsthand evidence of this phenomenon. "Different types of soils have different response to seismic waves," Yang said. They are excited about studying the trove of detailed data. He immediately called Utpal Dutta, also a UAA engineering professor, who worked for years on the network with Biswas. UAA geotechnical engineer Joey Yang said the earthquake was the strongest he has ever felt. But now we can really show you.' … This is absolutely clear evidence that certain areas have shakier ground than other places." "We always tell people, 'It's better to build on this kind of soil and not on that. "I think this is a huge teachable moment," West said. Then came the long wait for the kind of large earthquake that could activate the strong-motion sensors and give detailed data. Working out networking problems and other difficulties took years. West said it operates on shoestring funding through support from various agencies. The network took many years to fund and build. A thick network of 40 seismographs would operate continuously in fire houses, underground in drill holes, in high rises and parks, and elsewhere. In the 1990s, UAF seismologist Nirendra Biswas began advocating for a system of instruments in Anchorage that would show how the ground moves differently over our varied soils. In Turnagain, where scores of houses fell into cracks or sank into the ocean, new houses, roads and utilities were built over their ruins.Įarthquake experts have told me they would not live in those homes and they avoid some buildings downtown. The experts succeeded in limiting development on some of the slides, including in Government Hill and on Fourth Avenue, where the federal government paid for a massive stabilization project.īut the city overruled the experts to allow rebuilding along the bluff near L Street downtown. Downtown, they proposed allowing large structures only around Seventh Avenue, with land near the downtown bluffs restricted to parks and low buildings. The west side of town rests on a layer of clay that shakes readily and can turn to liquid with enough shaking.Īfter the 1964 earthquake, engineers and geologists tried to prevent rebuilding of some areas of the city where clay soils collapsed into slides that took down buildings. We've long known that the east side of town generally has stiffer soils and bedrock that resist shaking. Intensity of Sunday's earthquake measured at different locations around Anchorage. Figuring out those details is the point of the sensor network. We felt Sunday's shaking much longer than that - longer than a minute - because of the soft geology of Cook Inlet and the weak soils under the city, factors that amplified and extended the impact. The rupture in the Iniskin quake lasted only 10 to 15 seconds. The rupture in 1964 lasted 4 minutes, long enough to liquefy ground in Anchorage. West said the '64 quake did vastly more damage with massively greater motion and much longer duration. Sunday's measurements of 15% g in some neighborhoods - or shaking that is 15 percent as strong as the normal acceleration of gravity - are as high as Anchorage is believed to have experienced in the massive 1964 earthquake that transformed the region.īut that quake was 1,400 times stronger the Iniskin Earthquake, as Sunday's event is called. Instruments in the network show the strength of shaking compared to the strength of gravity. "Since the network was installed more than a dozen years ago, this is the earthquake that people have been wanting to record from a data and research perspective," said s tate seismologist Michael West, who directs the Alaska Earthquake Center at the University of Alaska Fairbanks. The finding comes from one of the best urban seismograph networks in the country, conceived almost 20 years ago, installed a decade ago and receiving its definitive test Sunday. Sunday morning's magnitude-7.1 earthquake shook Anchorage neighborhoods with vastly different force even less than two miles apart, evidence that some pockets of the city are much safer than others. State seismologist Michael West shows the approximate location of the earthquake that shook the Interior early Wednesday, Oct. Updated: DecemPublished: January 25, 2016
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