![]() Seismic shaking “tends to get amplified near sharp breaks in slope,” while differences in seismic properties between intact bedrock and loose fill cause “seismic waves to be trapped in the softer, loose material and they reflect back and forth,” he said. Two phenomena are at work in these settings that can lead to damaging cracking, said Jibson. ![]() ![]() One of the most damaging types of ground failure was extensional cracks, particularly at the boundary between natural and artificial slopes and areas graded flat for buildings. Some Anchorage homeowners and businesses reported ejected sand in crawl spaces and cracked foundations due to liquefaction settlement. Landsliding in the River Heights neighborhood of Eagle River, for instance, moved houses off their foundations and severed utility lines, while earth slumps blocked an off-ramp to International Airport Road in Anchorage. Each of these types of ground failures caused significant damage in the area, the researchers concluded. Jibson and his colleagues surveyed the Anchorage region on foot and by helicopter in the days after the 2018 earthquake to catalog a variety of ground failures caused by the earthquake, from landslides to liquefaction to ground cracking. “But now we have seen enough earthquakes to know that it’s not just magnitude that affects landslides, it’s also focal mechanisms and tectonic settings and the frequency of earthquake waves.” Ground cracks at the top of a steep valley wall in south Anchorage. “For the past 30 years we’ve made comparisons based on magnitude alone,” he said. “We feel pretty strongly that one of the reasons the Anchorage earthquake didn’t trigger so many landslides is because it was an intraslab event,” he said.ĭata from the Anchorage quake are helpful for scientists like Jibson who study how earthquakes differ in producing landslides across the globe. Megathrust earthquakes like the 1964 event tend to produce longer durations and periods of shaking, said Jibson, which could trigger more and larger landslides. The 2018 Anchorage intraslab quake, on the other hand, originated within a tectonic plate and at a greater depth than the 1964 quake. The 1964 Alaska quake was a megathrust event, where the rupture took place along the subducting boundary between two tectonic plates. Other differences between the 19 earthquakes might help to explain these findings, said Jibson. “I think was well below what it would take for them to really take off and move again.”Īfter a major survey of ground failures caused by the 2018 earthquake, Jibson and his colleagues also noted many fewer landslides-several thousands fewer-than would be predicted for the area from landslide modeling based on earthquake magnitude. In places like Government Hill and Turnagain Heights, where devastating landslides had taken place in 1964, there were “cracks in the places where they had moved in 1964, but they just kind of oscillated in place,” Jibson said. The shaking that accompanied the 2018 earthquake was of a higher frequency and a shorter duration than shaking during the 1964 quake, both of which probably kept the 1964 landslides from moving downslope again, said Randall Jibson of the U.S. The level of tsunami danger is being evaluated for other US and Canadian Pacific coasts in North America, according to the NWS.22 October 2019–Major landslides triggered by the 1964 magnitude 9.2 Great Alaska earthquake responded to, but were not reactivated by, the magnitude 7.1 Anchorage earthquake that took place 30 November 2018, researchers concluded in a new study published in Seismological Research Letters. “Based on all available data there is no tsunami threat,” the National Weather Service Pacific Tsunami Warning Center said. Kodiak is near the northwestern tip of Kodiak Island, which is the largest island in Alaska and is the second-largest island in the US.Ī tsunami watch had been issued for Hawaii but was later canceled. Police in Kodiak, the largest town on the island of Kodiak, advised residents after the quake to move to high ground, adding that the high school was open as an evacuation location.Īs the alerts changed from warnings to advisories, the Kodiak Police Department said in a message, “Kodiak has been downgraded to Tsunami Advisory status however we are not all clear.” ![]() “A tsunami was generated by this event, but no longer poses a threat,” the center said. When it comes to earthquakes, size matters but so does the terrain Credit: USGS / Ben Brooks Ben Brooks/USGS/JPL/NASA A USGS Earthquake Science Center Mobile Laser Scanning truck scans the surface rupture near the zone of maximum surface displacement of the magnitude 7.1 earthquake that struck the Ridgecrest area. ![]()
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