RAPID: Collaborative Research: Subduction zone imaging following the 2018 Anchorage earthquake

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Subduction zones are places on Earth where one plate goes beneath another plate. They are responsible for numerous volcanic eruptions and earthquakes, as the recent Anchorage earthquake. Important dynamical processes take place in between the two converging plates, such as the buoyant rising of molten mantle rock below volcanoes. Seismology offers a direct way to image the convective zones of subduction, which are between 30 km and 200 km deep. Seismometers installed in the field record seismic waves from earthquakes occurring in the down going plate and all over the world. By modeling the wave forms and timing, using techniques like those used in medical ultrasound imaging, images of the subduction zone can be obtained. Here, the project team will install more than 300 seismometers above the Alaska subduction zone. It will take advantage of the seismic waves produced by the ongoing aftershocks from the Anchorage earthquake to image at high resolution the subsurface structures. This project will also test the imaging capabilities of the timely deployment of dense networks of small seismometers, a new approach in seismology. It will provide critical constraints for models of subduction zone dynamics and associated hazards, as well as field experience to seven students in seismology. This RAPID project will support the deployment of 306 seismometers (three-component nodal sensors) to image the Alaska subduction zone at an unprecedented resolution. It will take advantage of the active local seismicity enhanced by the aftershocks of the 2018 magnitude-7 Anchorage earthquake. Recent results from Cascadia indicate that ambient noise and teleseism body waves can be used to image crustal structure. Here, local seismicity will be used to image the mantle wedge and crustal structure. Distant earthquakes will be used to image subsurface discontinuities, such as the crustal thickness and the subducting slab. Surface waves from ambient noise will be used to characterize the shallow crustal structure. This should allow resolving at km-scale the structural complexity within the mantle wedge between the subducting Pacific plate and the overlying North American crust. Furthermore, by leveraging an ongoing smaller-scale project focused on the Denali fault, this work will allow the simultaneous characterization of small-scale fault zone structures and broader crustal contrasts across the fault. Higher resolution images will provide important constraints for models seeking to understand the dynamics of subduction zones. The project is led by three early-career scientists and will involve seven students in seismology for the field deployment and recovery.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.