International Institute of Earthquake Engineering and Seismology

At 4:47 a.m. on March 31, 2006 an earthquake occurred in the South of Borujerd with several foreshocks, especially on March 30, 2006 with ML=4.6 and at 23:06 on March 30, 2006 with ML=5.1, and also with the aftershock at 5:01 a.m. on March 31, 2006 with ML=4.9 (Figure 1). According to the latest news reports, 66 fatalities, about 1280 injuries, and damage to 330 villages in the Darb_e_Astaneh (Silakhor) region (surrounding Borujerd and Dorud) have been reported. The occurrence of this earthquake near the main Zagros fault (section of Dorud fault) shows the probability of further activity from this fault (Figure 2). IIEES's report on the previous earthquakes on May 3, 2005 shows that in this same region, a number of earthquakes of which the greatest magnitude was 4.9 occurred on May 3, 2005 - and caused one fatality and great panic among people of this region. The epicenter of the earthquake on March 31, 2006, was in the southeastern epicentral region of the May 3, 2005 earthquake and with a greater magnitude indicates the continuous activity of the current fault plain in the earthquake stricken region.
The occurrence of eight earthquakes between May 3-5, 2005 in the Borujerd region, 17 consecutive earthquakes with a magnitude of 2.5-4 between 21- 27 of November, 2004 in the Poldokhtar region and other similar cases all indicate the high seismic activity of this area of the earth's crust.
With regard to the increase in seismic activity of the region, IIEES has dispatched a specialized team to the region on March 31, 2006 with the aim of preliminary identification of the earthquake stricken region and installing a temporary seismic network with 6 seismic stations in the region. Until now, more than 60 aftershocks have been recorded by the broad band seismic network of IIEES in the region (Figure 2).

Figure (1): Records of the 31.3.2006 Darb_e_Astaneh (Silakhor), Lorestan earthquake and aftershocks at the IIEES broadband stations (INSN).

Active faults

In general the main trend of the active fault in the Zagros is in NW-SE and the main active faults in the Lorestan Province are shown in the Figure 3.

Figure (2): Map of the earthquake's epicenter on 31.3.2006 Darb_e_Astaneh (Silakhor) ML=6.1 and foreshocks and aftershocks of the earthquake (green circles are foreshocks and red circles are aftershocks).

Seismicity

The Zagros region is one the most active region in Iran (Figure 3). Table 1 shows the main instrumental seismic events in the Lorastan province.

Figure (3): Map of main faults and previous seismic events in Lorestan Province.

Table 1: Main seismic events in Lorestan Province (source IIEES website)

Preliminary Action taken by IIEES:

IIEES has sent a team of multi-disciplinary experts to the region on 31.03.2006 to area and the result of observation will be posted soon at the www.iiees.ac.ir web-site.

According to the report the loss of life and property has been heavy. There is preliminary assessment of the event in FARSI at the www.iiees.ac.ir .

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