Research

Planetary Seismology

Quakes on other planetary bodies are different than on the Earth. The two other bodies that have data are our moon and Mars. Both of them are much smaller than the Earth and without current plate tectonics to drive quakes. Thus, the quakes that do occur are much smaller, but the smaller quakes can be detected on global scales since the planetary bodies are smaller as well. No atmosphere on the moon also means no thermal protection. The figure shows 12 quakes coming from the base of the lunar module as it heats up in the lunar morning. There is one moonquake coming from the surface as it heats up. A very thin layer on the surface of the moon, called the regolith, has been bombarded by meteors for billions of years and is unconsolidated material with very low seismic wave speeds. We would expect this region to dissipate seismic waves quickly, however seismic signals from small moonquakes can last for 10's of minutes. This is similar to seismic waves in the Mexico City basin where seismic wave durations are very long in the sediments that used to be a lake. What can we learn about with seismology by comparing the Earth and other worlds?

Regional Structure

I have used a variety of techniques with my colleagues and my students to determine tectonic structure including standard seismic tomography techinques, but have also magnetotelluric soundings and geologic evidence to understand the structure.

Slow Earthquake Phenomena

Slow Earthquake Phenomena include a large spectrum of measurable signals including slow slip events, tremor, low frequency earthquakes and very low frequency earthquakes. My students developed a single‐station tremor spectrum template detection method that we applied to seismic stations in Mexico. The resulting catalog demonstrates the strong correlation of tremor activity and aseismic slip over multiple slow slip cycles. We can use it to precisely determine when slow slip starts and stops, thereby allowing us to look for interactions with regular earthquakes. I am now applying the technique in other places in the world.

Network and catalog analysis

Seismic networks like the Southern California Seismic Network have been installed for decades. I look for trends over long time scales and evaluate the network itself and our assumptions about earthquakes. The figure shows a simple example of earthquakes M > 7 before the year 1900 (blue) and since 1900 (red) in Japan. The earthquakes before 1900 obviously do not represent the locations of earthquakes recorded by seismic networks since 1900. How can we maintain continuity in a seismic nework like the SCSN for future generations while also improving the network? How has our product changed over time?