Seismic Source Mechanism in Northern Thailand

During September 1997 to January 2000

Abstract

The idea of downloading seismic signals to any P ersonal Computer elsewhere to analyze and dete

rmine preliminary solution of seismic parameters e.g. origin time, epicenter, and magnitude, had b een initiated. To achieve this aim, an excellent co

mputer software called DIMAS (Display, Interacti ve Manipulation and Analysis of Seismograms) w as applied to solve the seismic source mechanism

of northern Thailand, detected by the IRIS and DIMAS at CHTO during September1997 to January 2000. This software cannot only determi

ne the basic parameters of an earthquake but als o identify the focal mechanism that caused the ev

ent.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.

Potential Seismic Source Zones in Continental Asia So

urce : http://seismo.ethz.ch/gshap/eastasia/

Seismotectonic Map in Continental Asia Source : http://

seismo.ethz.ch/gshap/eastasia/

Seismicity Map of Thailand and

Adjacent Areas Source :http://www.dmr.go.th

Fault zone LatitudeLongitude

(N.) (E.)

Chiang Saen 19.5-20.599.0-100.5Mae Tha 18.5-19.598.5-99.5Thoen 17.5-18.599.0-100.0Phrae 17.5-18.5100.0-101.0Moei-Uthai Thani 17.0-18.5

98.0-99.0Mae Hong Son 18.5-19.597.5-98.5Phayao 18.5-19.599.5-100.5Nan 18.5-19.5100.5-101.5Sukhothai 16.5-17.5 99.0-100.0Uttaradit 16.5-17.5100.0-101.0

Map of fault zones in northern Thailand

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

Fault Types

dip fault type(deg.)

-0 30 thrust31-44 reverse

-4584 normal-8590

-strike slip

Fault Zone Dip (%) Average - 030

-3144 -4584

-8590

Chiang Saen 1333.2333. 5667 667.

5301. Mae Hong Son 2667. 000.6000. 1333.

5608. Mae Tha 1000. 500.7000. 1500.

6776.Phayao 000. 1176.

5294. 3529.7253.Nan 000. 5000.2500. 2500.6012.

- Moei Uthai Thani 2857.000. 4286. 2857.

6405.Thoen 1000.2000. 6333. 667.

5624.Phrae 1000.4000. 4500. 500.

4 9.73Sukhothai000. 3333.6667. 000. 45.58Uttaradit 3333. 000.

6667. 000. 39.97

Dip Distribution of Seismic Source Zones in Northern Thailand

Seismicity and Source-Mechanism Map of Northern Thailand

End

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