Seismic Lg-wave attenuation tomography: Method, algorithm, data processing flow and application

Abstract

With the rapid development of modern seismic network, seismological signals can be digitally recorded in broad frequency band, larger dynamic range, and higher spatial density, which provide the possibility of obtaining fine structures of the quality factor Q in the earth by using a large number of high-quality seismic data. Lg wave is one of the most significant seismic phases at regional distances. As a guided wave (or superimposed higher-order surface waves) propagating in the crust, the Lg wave is often used for investigating crustal attenuation. This study systematically reviews the method for broadband Lg wave attenuation investigation, including the formulation of the tomographic inversion system and its relation with the data. We address many practical details regarding the data processing, including the regional seismic data collection, sampling the Lg signals and noise series, noise analysis, and data quality control, and the preparation of the single-station, two-station, and two-event data sets. We also briefly describe how the attenuation results can be applied to understand various geology, geophysics, and geodynamic problems. As an example, we demonstrate a complete workflow for investigating the Lg wave attenuation in the Taiwan Island in China and the surrounding region. Based on 8650 vertical-component seismograms from 416 earthquakes recorded by 86 broadband digital stations, we construct a high-resolution broadband Lg attenuation model in the study region. The frequency covers 0.05～10.0 Hz, and the resolution can reach to about 0.25º×0.25º in areas with the best data coverage. The tomographic results reveal significant lateral variations of crust Q values in the study region. The Taiwan Island is generally characterized by high Q. The surrounding regions are mostly in low Q, e.g., the Nanri Island basin in northeast Taiwan, the Tainan basin in southeast Taiwan, the collision zone between the Philippine and the Eurasian plates in eastern Taiwan, the Huadong basin, the Ryukyu arc, and the Okinawa trough, are all highly attenuated. These low-Q areas are likely related to strong tectonic activities due to plate collisions.

Keywords

• lg wave
• crustal attenuation
• q tomography
• inversion method
• data processing
• taiwan island