Researchers: Ronni Grapenthin, New Mexico Institute of Mining and Technology, Michael West, Alaska Earthquake Center and Jeff Freymueller, University of Alaska, Fairbanks
Written by Linda Rowan
31 August 2017
A retrospective analysis of the 2016 M7.1 Iniskin earthquake shows how geodetic observations from GPS sites in Alaska may augment earthquake early warning. For a large magnitude earthquake that originates at a shallow depth, information about the surface waves from GPS sites can provide some warning before the shaking arrives in populated areas such as Anchorage. In addition, even if the geodetic data cannot provide sufficient warning before damaging shaking, it can rapidly and precisely define the earthquake characteristics to help with response and triggered hazards such as landslides and tsunamis.
Geodetic data from real time GPS/GNSS networks can quickly provide crucial information about the size of an earthquake and the amount and direction of the shaking. If geodesists can characterize the earthquake before the damaging shaking arrives at a population center, it can provide early warning. If the characterization is completed later, it can still inform the public and responders about where the greatest dangers or damages are and whether triggered hazards like landslides or tsunamis might follow.
Now some earthquake and tsunami warning systems are beginning to integrate geodetic observations into their workflow. These observations can be particularly valuable where the geodetic infrastructure already exists and where the seismic network is limited. It is also recognized that for very large earthquakes (greater than magnitude 8) nearby seismometers will saturate and cannot provide rapid information about the actual magnitude of the event.
Most of the efforts to augment warnings with geodetic data are still in a pilot project phase. Here the authors test whether a modest GPS network in Alaska, consisting of Plate Boundary Observatory (operated by UNAVCO) and University of Alaska sites, can contribute to earthquake early warning. A retrospective analysis of the 2016 moment magnitude 7.1 Iniskin earthquake in Cook Inlet of Alaska was performed.
The results show that for shallow events (originating at depths less than 50 kilometers) with a large magnitude (greater than magnitude 7), the geodetic observations can provide early warning of damaging shaking to populated areas of Alaska, such as Anchorage. Alaska has the potential for a very large magnitude earthquake (greater than magnitude 7) that could trigger a damaging tsunami. Given that the seismic network in Alaska is limited, the existing geodetic network, that is modestly extensive, could augment early warning and provide for rapid characterization of large events to improve response. It would be essential to convert some of the geodetic network to real time sites to ensure the practical early warning demonstrated by this study.
The Utility of GNSS for Earthquake Early Warning in Regions with Sparse Seismic Networks, Ronni Grapenthin, Michael West, Jeffrey Freymueller, Bull. Seismol. Soc. Am., 2017, doi:10.1785/0120160317.
earthquake early warning, magnitude
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