Identification of a nascent tectonic boundary in the San-in area, southwest Japan, using a 3D S-wave velocity structure obtained by ambient noise surface wave tomography

Abstract

We derived a three-dimensional S-wave velocity model for the San-in area of southwest Japan to examine heterogeneous structures such as tectonic faults. Many earthquakes occur in this area, but much of the activity has been relatively recent, so the fault distribution has yet to be fully clarified. Here, we used continuous ambient noise data from a dense seismic network, deployed from November 2009 to extract Rayleigh and Love wave dispersion data between station pairs, and then applied a direct surface wave inversion to the phase velocities of each station pair to determine a three-dimensional S-wave velocity model. In the resulting model, faults and a previously unrecognized tectonic boundary appeared as low-velocity anomalies or velocity boundaries, and the velocity anomalies were also associated with many past earthquake hypocenters. These results contribute to our understanding of heterogeneous structures caused by recent tectonic motion and of possible future tectonic activity, such as intraplate earthquakes. Surface wave tomography using ambient noise recorded in dense seismic networks could also be applied in other parts of the world to reveal new heterogeneous geological structures (i.e., unrevealed tectonic faults) and could contribute to disaster mitigation.

Tracking supercritical geothermal fluid distribution from continuous seismic monitoring

“…Then, we applied a direct surface wave inversion method 49 . This approach has been used in various studies to resolve shallow crustal features 50 – 52 . Prior to the zero-crossing step, the daily seismic waveform was divided into 30-min segments with 50% overlaps and bandpass filtered between 0.2 and 0.7 Hz.…”

Tracking supercritical geothermal fluid distribution from continuous seismic monitoring

“…Then, we applied a direct surface wave inversion method 48 . This approach has been used in various studies to resolve shallow crustal features (e.g., [49][50][51] ). Prior to the zero-crossing step, the daily seismic waveform was divided into 30-min segments with 50% overlaps and bandpass ltered between 0.2 and 0.7 Hz.…”

Ambient Noise Tomography for a High-resolution 3D S-Wave Velocity Model of the Kinki Region, Southwestern Japan, using Dense Seismic Array Data

“…To unravel heterogeneities within the crustal structure and upper mantle over a wide area, very few geophysical techniques with proven e cacy are available (Suemoto et al 2020). Active-source geophysical techniques such as seismic re ection and refraction can be used to map and characterize geological structures at high resolution.…”

“…Conversely, P-and S-wave travel-time tomography utilizing earthquake data over a wide area has provided signi cant results, resolving major structures such as faults and geologic boundaries (Matsubara et al 2008;Nakajima et al 2009; Yolsal-Cevikbilen et al 2012). Even so, the downside of this approach is that the resolution of geological structures depends on the distribution of natural earthquakes (Suemoto et al 2020). Using teleseismic data, surface wave tomography can also be applied.…”