Intermediate-depth earthquakes

How deep do earthquakes occur on Earth? Deep earthquakes, generally defined as earthquakes deeper than 70 km, are generated in a deeper portion of subduction slabs where the extremely high pressures and temperatures make frictional slip unlikely. Seismicity in the deep Earth can provide essential information on the physical processes that control fluid distribution within the mantle, yet the mechanism of deep earthquakes is still enigmatic.

Deep earthquakes are categorized into two groups depending on the depth. Intermediate-depth earthquakes generally occur at the depth range of 70-300 km, then deep-focus earthquakes continue from 300 km.

In our research group, we focus on intermediate-depth earthquakes in Colombia. The region shows “a nest of earthquakes” where intermediate-depth earthquakes densely occur within the 10-km cube. The Bucaramanga Nest in Colombia is one of the most productive areas of intermediate-depth earthquakes on Earth. We are curious about the mechanism of triggering many earthquakes in a limited volume within subduction slabs.

Currently, we are working on building a systematic catalog of earthquakes in the Bucaramanga Nest. The goal of our initial project is to detect smaller events that have not been identified in the original catalog by SGC to understand the background seismicity. After completing the catalog making, we will work on spectral analyses to find differences between regular earthquakes in shallow regions, slow-slip events in subduction zones, and other deep earthquakes in different regions. By comparing the source spectra, we will identify the fundamental mechanism of deep earthquakes.

Ayako was previously working on deep-focus earthquakes in Japan. After joining William’s group, she widely pursues her curiosity about deep earthquakes. She considers a key to revealing the mechanism of deep earthquakes buried in not only subduction zones on Earth but also other planetary bodies such as the Moon, Mars, and even Titan. All those planets have/will have installed man-made seismometers, and she hopes to work on those seismic data in the future.

Ayako Tsuchiyama
Ayako Tsuchiyama
PhD Candidate

I study the earthquake source.