GEOMETRY, FAULTING AND NEAR-SURFACE STRUCTURES AT THE MARGINS OF HAT YAI BASIN, SOUTHERN THAILAND: CONSTRAINTS FROM SEISMIC DATA

Sawasdee  Yordkayhun; Pattawee  Srirasa

Authors

Sawasdee Yordkayhun Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand.
Pattawee Srirasa Department of Physics, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla, 90112, Thailand.

Keywords:

Seismic reflection, shear wave velocity, MASW, Hat Yai basin, fault

Abstract

Hat Yai district and vicinity is located in Hat Yai basin, one of the thick Quaternary basin fills in southern peninsular, Thailand. Infrastructures development, urban planning, groundwater management and seismic hazard are the main concerns in this region. Therefore, two seismic reflection survey lines ranging from 2-3 km were acquired nearby the boundary of Hat Yai basin to characterize the subsurface and determine the basin geometry and the fault zones. Shear wave velocity (Vs) distribution and average Vs at the upper 30 m of the shallow subsurface (Vs30) were also extracted from the dataset based on multichannel analysis of surface wave (MASW) analysis. The results confirmed that the strata geometry of Hat Yai basin is a rift type basin with sediments fills that are fault-bounded. The shallow fault segments observed in the sections are characterized by high angle, indicating extension in nature. Three Quaternary sedimentary units were distinguished in the upper 200 m depth of the basin. However, the contact between bedrock and sedimentary sequences within the basin was not clearly imaged on the seismic sections due to the source power and resolution limitation. Knowledge of fault zone structure and Vs distribution in the shallow subsurface is important for understanding seismic hazard and risk in the basin.

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