金曜日セミナー:(2019年6月28日) Zack Jack SPICA

2019/06/28 16:00〜17:00  東京大学地震研究所2号館 第1会議室

Distributed acoustic sensing: game changing for seismology?

Our understanding of subsurface processes suffers from a profound observation bias: ground-motion sensors are rare, sparse, clustered on continents and not available where they are most needed. A new seismic recording approach, called distributed acoustic sensing (DAS), can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recording over tens of kilometers of linear fiber length.

I will present two recent studies based on such technology. The first is in the city of Stanford, California, where we use a fiber cable directly laying in an air-filled PVC conduit under the road and normally operated by the Stanford IT services. These measurements are used to provide geotechnical information at a scale normally unattainable (i.e., for each building) with traditional geophone instrumentation. In the second study, we show how downhole DAS passive records from the San Andreas Fault Observatory at Depth can be used for seismic velocity estimation. Using data recorded from both earthquakes propagating near‐vertically and ambient seismic noise, we compute seismic velocities (Vp and Vs) with a resolution of the order of the meter, which allows us to shed light on the structure of the rock surrounding the San Andreas fault.