Investigation of Focal Mechanism and Fractal Dimension Inthe Thailand-Laos-Myanmar Borders

Abstract

According to Indo-Australian and Eurasian plate collision, a large number of seismogenic fault zones were dominant as the intraplate earthquake sources in the Mainland Southeast Asia including the Thailand-Laos-Myanmar border (TLMB). In this study, we investigated the mechanism of earthquake faulting and pattern of earthquake occurrence in this region. Based on focal mechanism data reported by the Harvard Moment Centroid, the average fault movement was strike-slip faulting in NE-SW direction. The angle of fault dipping varied between 65 and 85 degree with rake angle revealing left lateral movement. In addition, we investigated 8 significant faults in TLMB such as Nam ma, Mengxing, Dein Bein Fu. The mechanism illustrates differently strike-, oblique- and dip-slips. In order to clarify the earthquake pattern, fractal dimension (Dc) was calculated with both dataset of before- and after-declustering process. In addition b value of the frequency-magnitude distribution was also analyzed. As a result for spatial investigation, the northern Thailand and eastern Myanmar reveal comparatively low b, between 0.5-0.8. Meanwhile, the other areas are comparatively high with b ranged 0.8-1.2. In temporal investigation, b value decreases continuously before both Mae Lao and Tarlay earthquakes posed and the Dc values are drop down suddenly during these earthquakes were generated. For b-Dc relationships, Mae Lao earthquake indicate the positive relation while Tarlay earthquake express negative relation. This relation, therefore, may accord to the different characteristic or activities of each fault zone.