Title: Inference of the thermodynamic state of the upper mantle beneath Alaska by using body wave teleseismic tomography
Abstract:
Tomography models of seismic attenuation and seismic velocity provide valuable and complementary information about the Earth’s thermodynamic state, as these parameters possess different sensitivities to various mantle properties. Despite the potential for combining these two observations, challenges in measuring attenuation have often hindered their joint use at regional scales. Alaska’s complex tectonics, diverse thermodynamic conditions, and the excellent seismic coverage provided by the Transportable Array (TA) deployment make it an ideal natural laboratory to assess the power of new high-resolution regional models of attenuation and velocity to provide insights into the upper mantle’s physical conditions. We have updated an attenuation measurement approach that simultaneously fits the amplitude and phase components of the differential attenuation operator and tests teleseismic signals for elastic focusing and defocusing effects, which can contaminate attenuation measurements. With this update, we generated thousands of high-quality differential attenuation measurements and inverted them using our iterative inversion algorithm, which accounts for potential order-of-magnitude variations in the quality factor, Q. We also obtained differential travel-time measurements, which were independently inverted to construct three-dimensional velocity tomographic models. Our models display consistent large-scale regions in the mantle, including a fast-velocity, low-attenuation subducting slab, a high-attenuation, low-velocity mantle wedge, and the Seward Peninsula. We finally used these observations of Q_S and V_S to establish 3-D models of the likely distribution of temperature (T), melt fraction (ϕ), and grain size (d), by applying a joint Bayesian inference framework using the Very Broad Rheology calculator (VBRc). As a key part of a multidisciplinary initiative, these new results will make significant contributions to understanding the full spectrum of the Earth’s rheological response.
Biography: Cristhian Salas is a Ph.D. Candidate in seismology at the University of California, Santa Barbara. Previously, he obtained a Geology degree at Yachay Tech University in Ecuador, and his Master’s degree in Geophysics at Michigan Technological University in 2021, where he worked on seismic interpretations of focal mechanisms on the Yellowstone Plateau. His current research focuses on understanding rheology using seismic data.
Contact: csalaspazmino@ucsb.edu