1. Seismic Source Mechanism in Northern Thailand
During September 1997 to January 2000
Abstract
The idea of downloading seismic signals to any Personal Computer elsewhere to analyze and determine preliminary solution of seismic parameters e.g. origin time, epicenter, and magnitude, had been initiated. To achieve this aim, an excellent computer software called DIMAS (Display, Interactive Manipulation and Analysis of Seismograms) was applied to solve the seismic source mechanism of northern Thailand, detected by the IRIS and DIMAS at CHTO during September1997 to January This software cannot only determine the basic parameters of an earthquake but also identify the focal mechanism that caused the event.
During this period, it was found that most earthquakes occurred in the area were resulted from the mechanism mainly of normal faults. Their major trend is northeast-southwest which is the same direction of major faulted graben in northern Thailand. The collision of the Indo-Australian plate and the Eurasian plate is considered to be the main driving force that has caused faulting and induced seismicity in this region.

2. Potential Seismic Source Zones in Continental Asia Source : http://seismo.ethz.ch/gshap/eastasia/

3. Seismotectonic Map in Continental Asia Source : http://seismo. ethz

4. Seismicity Map of Thailand and Adjacent Areas Source : http://www. dmr

5. Fault zone Latitude Longitude
Chiang Saen
Mae Tha
Thoen
Phrae
Moei-Uthai Thani
Mae Hong Son
Phayao
Nan
Sukhothai
Uttaradit

6. Map of fault zones in northern Thailand

7. Map of active faults in Thailand and adjacent areas(Lacassin et al., J. Geophys. Res., 1997)

8. Fault Types

9. dip fault type
(deg.)
0-30 thrust
reverse
normal
strike-slip

10. Dip Distribution of Seismic Source Zones in Northern Thailand
Fault Zone Dip (%) Average
Chiang Saen
Mae Hong Son
Mae Tha
Phayao
Nan
Moei-Uthai Thani
Thoen
Phrae
Sukhothai
Uttaradit

11. Seismicity and Source-Mechanism Map of Northern Thailand

12. End

13. The examples of particle motion analysis of events during the period of the study