Based on Waveform Modeling of INSN Broadband Data

Moment tensor solution of the main shock and the only aftershock with magnitude above 4 (Mw) are presented here. The modeling has been carried out using Dreger’s (Dreger 2003) method which is based on time domain, full waveform three component modeling of seismograms for obtaining the components of seismic moment tensors. The data comprise broadband recordings of 4 stations of Iran National Seismic Network (INSN) within regional distances from the analyzed events. Locations of the events and the waveform fits are presented below. The solutions show mainly reverse faulting with some component of strike slip movements.

1- The Main-shock

The main shock occurred on the afternoon of June 18th, 2007 and was measured 5.5 (mb) by IIEES and located about 150 km southwest of Tehran near the major city of Qom.

 

Location of the event , Waveform fit

2- The Major aftershock

Most of the aftershocks recorded in the aftermath of the main event have been small magnitude quakes. Only one aftershock a day after the main shock was above 4 in magnitude and its solution is presented here.

 

Location of the event , Waveform fit

References

• Dreger, D. S., 2003. TDMT_INV: Time Domain Seismic Moment Tensor INVersion, International Handbook of Earthquake and Engineering Seismology, Volume 81B, p 1627.
• Engdahl, E.R., R. van der Hilst, and R. Buland, 1998. Global teleseismic earthquake relocation with improved travel times and procedures for depth determination, Bull. Seism. Soc. Am. 88, 722-743.

Location of the event

Waveform fit (Main-shock)

Waveform fit (Aftershock)

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 .

Pictures

At 11:01 (local time) an earthquake with surface wave magnitude of 5.9 occurred 85 kilometers southeast of Hajiabad, Hormozgan and 105 km northwest of Kahnooj, Kerman (Figures 1,2). This seismic event was recorded at 13 broad band seismic stations of the Iranian National Broad-Band Seismic Network (INSN) at IIEES (Figure 3). According to the recorded seismograms, this earthquake is located at 28.18˚ N and 56.76˚ E. The village of Ab Bid of Faryab and also the villages of Ahmadi and Bagh Chenar in the epicentral area have been most severely damaged. This earthquake was completely noticeable in the cities of Kerman, Jiroft, Kahnuj, Faryab, Fahraj Soghan, Baft and Manujan.

Figure (1): Map of the earthquake’s epicenter according to (EMSC, NEIC, IIEES) and the most severely damaged villages

Figure (2): Earthquake Epicenter of Feb. 28, 2006; Southeast of Hajiabad

Figure (3): Recorded Seismograms; Earthquake Southeast of Hajiabad (Iranian National Broad-Band Seismic Network of IIEES)

Figure (4): Seismicity of the 200 km range surrounding the earthquake epicenter

Figure (5): Earthquakes with magnitudes of 6 and greater than 6 of the 200 km range surrounding the earthquake epicenter

Table (1): List of earthquakes with magnitudes of 6 and greater than 6 of the 200 km range surrounding the earthquake epicenter

Figure (6): Seismicity map of the region during the past 3 months (November 27, 2005- Feb. 28, 2006)

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(b)

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Figure (7): Recorded Seismograms of the Faryab Earthquake at International Seismic Stations of IDC

At 2:45 (local time) an earthquake with magnitude of 5.2 on the Richter scale occurred 24 km North of Masjed Soleiman and 28 Km south east of Lali in the province of Khozestan (Figure 1). This seismic event was recorded at 13 broad band seismic stations of the Iranian National Broad-Band Seismic Network (INSN) at IIEES (Figure 2). Wave forms of this earthquake may be seen on the IIEES website. According to the recorded seismograms this seismic event is located at 32.15 ˚N and 49.23 ˚E. During the previous month, more than 15 earthquakes have occurred at a radius of 100 km of this earthquake with magnitudes between 2.5 and 4 on the Richter scale (Figure 3 and Table 1). Many aftershocks have followed the main shock, of which 6 have been located by the Iranian National Broad-Band Seismic Network (INSN) of IIEES (Figure 4).
According to reports from various regions of the town of Lali, there has been more than 40 percent damage to 2000 housing, domestic and commercial units of this town. Greatest damages have been to domestic units in the village of “Ahmadabad Berkeh”. A number of the resident’s cattle have been trapped under the debris. 11 people have also been injured in this earthquake.

Figure (1): Epicenter of Earthquake- December 26, 2005- North of Masjed Soleiman

Figure (2): Recorded Seismograms of Earthquake- North of Masjed Soleiman (IIEES National Broad Bank Seismic Network)

Figure (3): Distribution of earthquakes occurring at a radius of 100 km in the previous month

Figure (4): Distribution of aftershocks

Table (1): The region’s earthquakes in the previous month

Figure (5): Instrumental earthquakes greater than 5 at a radius of 100 km surroundingthe earthquake epicenter- North of Masjed Soleiman

Table (2): Earthquakes of the region with magnitude greater than five

Table (3): Historical earthquakes of region

M7.6
10 KM Depth
96 KM (60 MI) NE OF Islamabad Near Pakistan-India Border
8:50 AM Local Time

• Severely Impacted Pakistan and India
• Limited Impact in Afghanista
• Severe Ground Shaking Lasting Almost 1 Minut
• Collapsed Apartment Building
• Collapsed School
• Village House Flattene
• Loss of Function of Infrastructure
• Aftershocks (Including M6.3)
• Destructive Landslides
• People Running Outside Homes and Offices
• At least 20,000 Killed
• Many More Injured
• Trapped Survivors
• Disrupted Communications
• Power Outages

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