We analyze the data recorded by the “Stanford DAS Array” for 6 seismic events cataloged in the USGS online database. Two of these events are man made (blasts at a nearby quarry), and 4 are earthquakes spanning a range from a local event that occurred less than 4 km from the array to a large quake offshore Cape Mendocino in North California. The data from two seismometers installed on Stanford campus at Jasper Ridge help to validate and interpret the data recorded by our DAS array. The analysis of the two quarry-blasts demonstrates that both kinematics and waveforms are recorded by the DAS array with excellent repeatability. We show that the time of the first-break of P-wave arrivals can be reliably measured from the DAS array, notwithstanding the loose coupling of the fiber-optic cable with the ground, and the known limitations of DAS to record events with particle motion orthogonal to the fiber cable. P-wave waveforms are more challenging to analyze because of the complexity of the wavefield, probably caused by strong local scattering. All the events we analyzed show that kinematics of S and surface waves can be reliably measured from the data recorded by our DAS array. Because of noise and uncertain coupling, it is more challenging to assess the quality of the waveform shapes and amplitudes than the kinematics. DAS recording of propagating waves with particle displacement orthogonal to the propagation direction are subject to a phase rotation that is dependent on the fiber-cable direction. When we apply an approximate correction for this phase rotation the spatial coherency of S-wave and surface-wave arrivals substantially improves.
Presentation Date: Monday, September 25, 2017
Start Time: 3:05 PM
Location: 362D
Presentation Type: ORAL
