Alaska megathrust 1: Seismicity 43 years after the great 1964 Alaska megathrust earthquake

作者：Li Jiyao^*; Abers Geoffrey A; Kim YoungHee; Christensen Douglas

来源：JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 2013, 118(9): 4861-4871.

DOI：10.1002/jgrb.50358

• Megathrust location
• 1964 Alaska Mw 9
• 2 Earthquake
• Interseimic period
• Yakutat terrane
• Microseismicity relocation

The largest moment release during the 1964 Mw 9.2 Alaska earthquake was on the portion of the megathrust under the eastern Kenai Peninsula and the Prince William Sound. The area is currently locked geodetically and corresponds to where the Yakutat terrane is subducting. In 2006-2009, a seismic array consisting of 34 broadband seismometers was deployed in the region. An automatic algorithm was used to detect 12,563 local earthquakes using 13months of data from the experiment. Of these, 9427 good quality earthquakes could be relocated in a joint inversion for hypocenters and velocity structure. They were then relocated by double difference to generate a final catalog of 8308 hypocenters. These microearthquakes delineate a deeper steeply dipping Wadati-Benioff zone contiguous with an 11km wide seismic zone dipping at 3 degrees between 20km and 40km depth along the 1964 earthquake%26apos;s rupture zone. Focal mechanisms do not show interplate thrust faulting events, but mostly normal faulting events with T axes generally parallel the slab dip direction, indicating them to be intraslab seismicity. The shallow narrow band of seismicity lies within the subducting Yakutat terrane and right below the thrust zone. Possibly, thrust faulting has not yet resumed yet in this early phase of the earthquake cycle. Thick subducted sediments overlying the Yakutat terrane could also form a large strong contact zone on a relatively smooth plate boundary, which does not favor seismic sliding on small patches but ruptures homogenously in great earthquakes.

• 出版日期2013-9