The Mechanics of Deep Earthquakes

Deep earthquakes are one of the most puzzling and spectacular seismic phenomena in Earth. They occur mostly in subducting slabs and pose significant seismic hazards in many regions around the world (although not as hazardous as shallow earthquakes). A better understanding of deep earthquake physics will greatly improve our understanding of subduction dynamics as well as the plate tectonics in general. The deep seismic events between ~50-300 km are usually called intermediate-depth earthquakes, and the earthquakes within the mantle transition zone are termed as deep-focus earthquakes. For my study, I mostly focus on the intermediate-depth earthquakes.

The intermediate-depth earthquakes often form a double seismic zone (Wadati–Benioff zone) along subducting slabs, and the origin of these earthquakes has been in debate for decades, since rocks at these depths are expected to deform plastically under the P-T conditions in the mantle rather than faulting. Faulting mechanisms and geodynamic interpretaions of such deep seismic events remain as one of the major unanswered questions in Earth Science. My study is to use high-pressure "labquakes" to simulate these deep earthquakes in a more controlled environment than our mother nature to better understand the physics of these deep earthquakes. This is the main project for my postdoc work at GSECARS under the guidance from Prof. Yanbin Wang.

By attaching an acoustic sensor (e.g., PZT transducers) on the back of each of the six anvils in the DDIA-module, we can use acoustic emission, an analog of earthquake, to study the brittle behavior of rocks at high confining pressure and temperature conditions corresponding to those in Earth's mantle. Controlled deformation of the sample with stress measurements by in-situ X-ray diffraction and strain measurements by radiography, coupled with in-situ acoustic emission monitoring, provides a very powerful way to look at the fracture and seismicity development in the rock sample. For intermediate-depth earthquakes, the commonly used hypothesis currently to explain their origin is the so-called "dehydration embrittlement", while our studies now start to challenge the original concept of this "dehydration embrittlement", and we find out that metamorphism-facilitated transformational faulting may also play an important role in generating intermediate-depth earthquakes, especially for the lower seismic zone along subducting slabs. Collaborating with seismologists from Gatech, and modeling experts from UIC, our results will shed new lights on the mechanics of intermediate-depth earthquakes.

This work is currently being prepared for publication. Please stay tuned...