Research - Susan L. Bilek, New Mexico Tech Earth & Environmental Science

My main research interests focus on earthquake processes. Current study areas include one close to home in the New Mexico area, and more far-flung areas in the shallow subduction zones around the world. One common thread to most of my work is to examine important factors influencing the nature of seismicity.

Part of my research effort while at New Mexico Tech includes monitoring earthquakes in New Mexico through the New Mexico Tech Seismological Observatory. Several students, both undergraduate and graduate, and I are currently locating earthquakes in the region of the Socorro Magma Body, a small active area that includes roughly half of all the seismicity in the state. Check out a video clip of me discussing a 2007 felt earthquake in Socorro here. These earthquake locations are combined with regional GPS observations to examine deformation of the magma body. In addition, we monitor seismicity throughout rest of the state using additional seismic stations in Carlsbad area.

Tsunami Earthquakes and Shallow Subduction Zone Earthquakes
Some of my research has addressed the occurrence of the tsunami earthquakes in the shallow subduction zones. I determined earthquake source durations for several hundred earthquakes in circum-Pacific subduction zones, finding a consistent trend of decreasing source duration with increasing depth in the subduction zone. This trend was used to estimate shear modulus, or rigidity, along the subduction zone plate interface. Low rigidity values I have estimated for the shallowest portion of the subduction zones are consistent with the hypothesis that the tsunami earthquakes occur in the shallow, low rigidity materials.

The global survey of shallow subduction zones provides a first step to examine depth dependence of earthquake source parameters. Next steps needed to further our understanding of earthquake rupture processes in the shallow subduction zone include focusing on the details of particular regions where additional local and/or temporary seismic networks complement data available from the global network. Andrew Newman of Georgia Tech and I are currently examining the 2006 Java earthquake as a likely "tsunami earthquake" candidate.

Middle America Subduction Zone
I also have research interests in Central America tectonics, with a few projects currently underway in Costa Rica. During 1999-2000, I was a member of a UC-Santa Cruz field project deploying several land and ocean bottom seismometers along the western Costa Rica margin. Along with co-workers at UC-Santa Cruz, Los Alamos, Georgia Tech, and several Costa Rican seismologists, we are looking at many aspects of the shallow subduction zone processes along the Middle America trench. These projects include examining the role of variable subducting topography on earthquake rupture processes in the region and defining the updip limit of seismicity in the subduction zone. Graduate student Jana Stankova is currently looking at stress drop variations along this margin, in collaboration with Los Alamos scientists.

Fault Modeling Studies
In collaboration with Carolina Lithgow-Bertelloni at U. Michigan and my previous graduate student Casey Elliott, I have been developing computer models to address questions of stress triggering and earthquake fault interactions. The first application of the modeling is along the Costa Rica margin, calculating the stress changes in the upper plate due to rupture of a subducting seamount. This will be an interesting combination study, as we will be able to correlate these stress changes with recorded seismicity from the UC-Santa Cruz local seismic network deployed in 1999-2000. Future areas of interest involve the possibility of stress transfer in several subduction zone earthquake cases and examining the effects of the free surface interactions with the earthquake rupture.