Collaborative Research: RAPID Geodetic Field Response to the 2018 Magnitude 7 Anchorage Earthquake

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On November 30, 2018 a magnitude 7 earthquake struck just north of Anchorage, Alaska and caused over $75 million in damage to private and public facilities. The earthquake took place in the upper part of a subducting slab where the slab may be bending downwards, and early indications suggest that the event was related to stresses caused by plate bending. In the weeks and months following a large earthquake, slip and deformation can continue to take place along a tectonic plate boundary. To better understand that nature of this deformation, this study would place five continuous GPS (global positioning system) stations near the earthquake epicenter, as well as record campaign GPS measurements at other local benchmark locations. Data from this study could be used to better understand the behavior along the Denali fault and improve constraints on local seismic hazards. This project focuses on constraining postseismic deformation due to the magnitude 7 Anchorage earthquake, a normal faulting event within the Yakutat flat slab, including how coseismic and postseismic deformation may trigger changes in slip along the subduction interface. To achieve this, five new continuous GPS sites will be installed in the near-field of the earthquake and repeat campaign surveys will be conducted at benchmarks throughout the region. These measurements will provide a dataset that will be able to more completely characterize postseismic deformation, variations in locking and creeping behavior on the subduction interface, and potential triggered slow slip events. The effect of intraslab normal-faulting earthquakes on upper plate deformation, coupling along the subduction interface, and transient events on the interface is not well understood. Coseismic displacements recorded at continuous GPS sites show a complex deformation pattern and the location of the event make it likely that viscoelastic relaxation in the asthenosphere will occur. Aftershocks recorded in the first weeks after the earthquake roughly delineate a horizontal surface, suggesting that the events may be occurring at or near the plate interface. The main shock occurred within a region that has experienced multi-year slow slip events in the past and studies in other subduction zones suggest that such regions are more prone to triggered slow-slip events after an earthquake. Along the eastern limit of the Yakutat flat slab, a postseismic study of the 2002 Denali earthquake suggested that that event may have caused long-term changes of the coupling along that section of the subduction interface. The sparseness of GPS sites within the aftershock zone makes it likely that transient changes on the underlying interface may go undetected and that postseismic deformation and changes in the coupling along the interface may not be able to be fully characterized. Data collected from the proposed new network of continuous GPS added to the data from existing continuous GPS and repeat surveys at campaign benchmarks will allow an evaluation of these signals at a more temporally and spatially dense scale than is currently possible.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.