A Preliminary Study of Shallow Crustal Velocity Structures along the Deformation Front of the Taiwan Orogen Revealed by Ambient Seismic Noise Tomography
Abstract
Taiwan is located on a complex convergent plate boundary zone where the Philippine Sea plate interacts with the Eurasian plate and it is accompanied by high seismicity and complex tectonics. The Western Foothills geologic province is located along the deformation front of the Taiwan Orogen with highly active faults and a complex seismogenic structure. The National Center for Research on Earthquake Engineering had been progressively established a temporary seismic network with ~40 broadband seismometers and an average interstation distance of ~10 km, to monitoring the seismicity and ground motion surrounding the three Science Parks between 2006 and 2010. The network covers most parts of the western-central Taiwan from Hsinchu to Tainan County.
Since the basic theorem of ambient seismic noise analysis has been verified, the investigations of subsurface velocity structures have provided important constrains in various parts of the world. The time domain empirical Green's function (TDEGFs) can be obtained from calculating the cross-correlation function (CCF) for each station pairs with simultaneous and continuous ambient seismic noise signals. We analyzed vertical components of the seismograms and the daily CCFs were calculated with a 200-s lag time in the 1-15-s period band using one-bit cross-correlation and spectral whitening for enhancing the spectral energy of the ambient seismic noise. The daily CCFs were stacked monthly and the monthly CCFs were then stacked to retain coherent signals for acquiring TDEGFs. Phase image analysis and far-field approximation methods employed to measure 1-10-s Rayleigh-wave phase-velocity dispersion curves. Tomographic method was applied to preliminarily construct Rayleigh-wave phase-velocity maps with 0.1° grid spacing. Lateral velocity variations showed dramatic patterns among different geologic provinces. Shallow crustal S-wave velocity structures will be further constructed, which is particularly important for the densely populated metropolitan areas in the western Taiwan. The cities are situated on thick alluvium and are threatened by seismic-wave amplification and soil liquefaction in historical records.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S23C0637H
- Keywords:
-
- 7212 Earthquake ground motions and engineering seismology;
- SEISMOLOGY;
- 7219 Seismic monitoring and test-ban treaty verification;
- SEISMOLOGY;
- 7255 Surface waves and free oscillations;
- SEISMOLOGY;
- 7270 Tomography;
- SEISMOLOGY