[S-SS11] Strong Ground Motion and Earthquake Disaster

[SSS11-P22] Calibrating Thailand’s local magnitude scale: a preliminary result

*Mongkolchai Sukmee¹, Sutthipong Noisagool^1,2, Satoru Tanaka³, Weerachai Siripunvaraporn^1,2, Songkhun Boonchaisuk^4,2, Yasushi Ishihara⁵, Taewoon Kim⁶, Hitoshi Kawakatsu⁷, Nozomu Takeuchi⁷, Kenji Kawai⁸, Yuki Suzuki⁸ (1.Department of Physics, Faculty of Science, Mahidol University , 2.Thailand Center of Excellence in Physics, Ministry of Higher Education, Science, Research and Innovation, 3.Volcanoes and Earth's Interior Research Center (VERC), Research Institute for Marine Geodynamics (IMG), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 4.Geoscience Program, Mahidol University, Kanchanaburi Campus, 5.Research Institute for Marine Geodynamics (IMG), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 6.Subduction Dynamics Research Center (SDR), Research Institute for Marine Geodynamics (IMG), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 7.Earthquake Research Institute, The University of Tokyo, 8.Department of Earth and Planetary Science, School of Science, The University of Tokyo)

Keywords:Local magnitude, Thailand, Richter scale

The local magnitude scale (ML) or Richter scale is a fundamental measurement for the regional earthquake study. The backbone digital seismic record in Thailand started in 2007, although there is no study in the local magnitude scale and its calibration. Using the ML without its calibration may lead to large uncertainty in the statistical seismology and geodetic study. In this study, we use the new seismic data from Japanese-Thai joint observation project, Thai Seismic Array (TSAR), and Mahidol University private stations to measure the attenuation characteristic of regional seismic waves. The total number of data is 79 earthquakes with 364 records. The Thai Meteorological Department (TMD) local magnitude is used as an initial value for the iterative grid search optimization. The station correction factor of each station also statistically calculate. The synthetic test on the implemented algorithm and data distribution are satisfied with an error of about 1% from the true attenuation models. For the real data, the geometrical factor, α, is 0.043 and the anelastic attenuation, k, is 0.0017. A best-fit solution of the distance (R in km) correction function from this data set is

-logA0 = 1.043logR + 0.00171R - 0.722.

The calibrated local magnitude is slightly different from Southern California and nearby regions such as Northern Vietnam. This magnitude scaling will be improved and further calibrate with more regional data.