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Information message about the earthquake in Taiwan on March 31, 2002

On March 31, 2002 the destructive earthquake has happened in Taiwan at 10:52 Moscow time (06:52 GMT).

Parameters of the earthquake have been determined in the Alert Service (AS) of Information Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad. Alert message on this earthquake has been delivered in 60 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 8 stations, accurate processing - with data 33 stations.

Figure 1 shows fragments of records with vertical components (BHZ) from digital stations, which were obtained by IPC in a near to real time mode: South-Sahalin (delta 28 degrees), Talaya (delta 31 degrees), Yakutsk (delta 38 degrees), Petropavlovsk (delta 39 degrees), Magadan (delta 40 degrees), Borovoe (delta 48 degrees). Figure 2 shows records of vertical component (BHZ) at digital stations Arti (delta 55 degrees), Garni (delta 66 degrees), Kislovodsk (delta 67 degrees), Lovozero (delta 68 degrees), Obninsk (delta 69 degrees), Pulkovo (delta 70 degrees).

Figure 1

Figure 2

IPC GS RAS also has obtained information with parameters of this event from some seismological centers, these data are given in table 1:

Table 1

NN	Time in origin h-min-s (GMT)	Lat degr.	Lon degr.	Depth km	N s/st	Ms/ N	mb/ N	I0 calc	GAP	Center
1	06-52-50.80	24	122	33	33	7.30/16	6.80/18	8.5-9		IPC GS RAS (accurate)
2	06-52-50.2	24	122	33	8	7.3/6	6.5/6	8.5-9		IPC GS RAS (preliminary)
3	06-52-53.4	24	122	33	297	7.2-7.3				CSEM
4	06-52-50.2	24	122	33	42	7.2/14	6.4/56			NEIC

IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences

CSEM - European - Mediterranean seismological center

NEIC - National Earthquakes Information Center of US Geological Service

Macroseismic manifestations

This earthquake has happened in island of Taiwan, which is located in one of the most seismic active regions of Pacific seismic belt. At least 2 men were killed, 15 are considered lost, 18 were injured. Financial center of Taipei was wrecked most of all. Messages were obtained about dozens of houses wrecked and water piping broken. Taipei subway has been stopped temporarily. Underground shocks with intensity 5 have been registered in Taipei, Ilan and Hualian. Authorities of Southern Japanese island Okinawa, which is nearly 500 km to the North-East from Taiwan, sent warning to local population about probable tsunami and recommended people to hide in places located at far distances from the coast line. Later this warning was cancelled. The late catastrophic earthquake with magnitude M=7.7 has happened almost in the same region on September 20, 1999. It killed 1500 residents.

Focal mechanism and seismic moment of the earthquake

Focal mechanism of the origin has been calculated with TMC method in National Earthquakes Information Center USA (NEIC), it is presented in table 2 and shown on fig. 3. As it is seen, the nodal plane NP1 has almost along latitudinal direction, another plane - NP2 - North-Eastern direction. Type of motion along both planes if thrust - under the action of predominant compression strengths, oriented in along meridian direction. The value of seismic moment Mo has been calculated in Obninsk with P-wave spectra, it makes 9.0*10**26 D*CM. The value of seismic moment Mo from NEIC is close to the value determined in Obninsk and they make 5.5*10**26 D*CM. The value of moment magnitude from data in Obninsk made Mw=7.3, NEIC - Mw=7.1.

Table 2

Axes of main strengths

Nodal planes

Center

NP1

NP2

Azm

Stk

Slip

Stk

Slip

276

160

269

117

NEIC

NEIC - National Earthquakes Information Center of US Geological Service

Figure 3