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Measuring Slip on a Complex Fault in Alaska

Researchers: Bin Zhao, Yujie Qi, Dongzhen Wang, Jiansheng Yu, Qi Li, and Caihong Zhang, China Earthquake Administration

Written by Linda Rowan
20 May 2019


Summary

A magnitude 7.9 earthquake on 23 January 2018 in the Gulf of Alaska broke multiple orthogonal fault segments. The GNSS data of ground deformation during and after the earthquake showed most of the slip on two west-southwest oriented faults. The earthquake does not appear to have increased the stress in the region of the magnitude 9.2 1964 Alaska earthquake.


Observations

The second largest earthquake (magnitude 9.2) documented in modern times occurred in the Gulf of Alaska in 1964. It occurred along a major plate boundary where the Pacific plate is subducting beneath the North American plate. The earthquake caused a damaging tsunami for nearby populations and as far away as Hawaii. Continued observations and models of this active plate boundary provide a better understanding of the fault mechanisms and the possible hazards of future earthquakes.

UNAVCO and others operate GNSS networks in Alaska and the rest of North America. These networks capture many earthquakes caused by the plate collisions around Alaska. A large magnitude event, moment magnitude 7.9 broke several fault planes at a depth of about 34 kilometers on 23 January 2018. The earthquake was close to the subduction zone boundary and sparked initial concern that the earthquake might grow into a major subduction event. Observations and modeling determined that the earthquake broke several fault planes in the Pacific plate above the plate boundary. The fault motion was complex and this work tries to decipher the complex deformation using observations and modeling.


Results

The GNSS observations of the earthquake, that is, the coseismic displacement, along with the aftershock distribution from seismic data, can be modeled as four intersecting faults, two directed mostly north to south and two directed mostly east to west. About 70% of the slip is on the east-west segments. Four zones along the eastern part of the subduction zone interface show a small increase of stress caused by the earthquake. The 2018 earthquake was complex, but it does not appear to have increased the stress very much on the subduction zone where the magnitude 9.2 1964 earthquake occurred.

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References

Coseismic Slip Model of the 2018 Mw 7.9 Gulf of Alaska Earthquake and Its Seismic Hazard Implications, Bin Zhao, Yujie Qi, Dongzhen Wang, Jiansheng Yu, Qi Li and Caihong Zhang, Seismological Research Letters (2018) 90 (2A): 642-648; doi: 10.1785/0220180141.

Keywords

Subduction zone, earthquake, coseismic, slip, post-seismic


Map Center
Gulf of Alaska


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