Influence of elastic properties around the shallow megathrust on tsunami earthquake rupture characteristics

American Geophysical Union Fall Meeting, 10-14 December 2018, Washington D.C.The seismogenic zone of megathrust faults at subduction zones hosts the largest earthquakes on Earth. These events are particularly hazardous and destructive, because the upper limit of the seismogenic zone lies offshore, so that coseismic deformation can affect the seafloor and generate tsunamis. Large tsunamis are typically caused by large and giant earthquakes of magnitude >8, but some remarkable exceptions exist. One of them is tsunami earthquakes, which generate anomalously large tsunamis for their size (typically M~7-7.5). Additional anomalous characteristics of tsunami earthquakes are a rupture concentrating in the shallowmost portion of the megathrust, a large discrepancy between their surface wave and moment magnitudes, a long source duration, and a marked depletion in high frequency content. In this work, we first examine a number of P-wave seismic velocity models of Circum-Pacific subduction zones to get the average depth variation of elastic properties above the inter-plate boundary. Then, we analyze the potential effect of the observed depth trends on different earthquake rupture characteristics including coseismic slip, source duration, moment rate spectrum, and surface wave magnitude. We show that the effect is substantial for all the computed variables, particularly in the shallowmost megathrust, indicating that this can be an important factor to explain the anomalous behavior of tsunami earthquakes as compared to deeper, regular eventsPeer Reviewe