|Observatories and Research Facilities for EUropean Seismology|
|Volume 4, no 2||September 2002||Orfeus Newsletter|
Destructive earthquake in Afghanistan (Hindu Kush) on March 25, 2002O. Starovoit, S. Yunga, I. Gabsatatova and L. Chepkunas
Geophysical Survey of Russian Academy of Science, 249020, Kaluga region, Obninsk, Lenin str. 189
The epicenter of the March 25 earthquake can be associated with the southern branch of the Darvaz-Karakul fault. The seismic history shows an earlier large shallow earthquakes that occured at approximately the same location, i.e. December 16, 1982 at 00:40:48.72 UT (36.148 N, 69.011 E, Mb = 6.2). It is interesting to note that this earthquake was preceded by a deep large earthquake on May 02, 1981, 16:04:52.8 UT (36.30 N, 71.20 E, Mb = 6.3).
The large shallow earthquake of March 25, 2002 occured three weeks after two large deep earthquakes on March 3, with magnitudes Mb of 6.2 and 6.6 respectively (locations 35.98 N, 69.17 E and 36.65 N, 70.45 E respectively).
Figure 1. Map of the earthquakes in Afghanistan. The location of the epicenters is determined by and published in the Obninsk seismological bulletin for the period 1955-2001. Blue is depth more 70 km, purple is depth in crust. The focal mechanisms of the earthquakes on March 3 and 25, 2002 come from the database of Harvard University Centroid Moment Tensor. Faults are marked yellow: DKF is the Darvaz-Karakul Fault and MKT is the Main Karakoram Thrust. The black arrow shows the direction of the plate motion of India relative to Eurasia (DeMets et al., 1990).
The shallow earthquake of March 25, 2002Preliminary earthquake parameters were determined by the Alert Survey (AS) of the Data Processing Center (DPC) of the Geophysical Survey of the Russian Academy of Sciences in Obninsk (Starovoit and Mishatkin, 2002). Digital and analog data from seismic stations of Russia, Commonwealth of Independent States (CIS) countries (Kirghizia, Kazakhstan, Turkmenistan, and Ukraine) and abroad(Norway and Alaska, USA) have been used. Subsequently, an alert message of this earthquake was sent to the Ministry of Emergency of the Russian Federation (EMERCOM) within 50 minutes after its occurence.
Preliminary analysis of this event was done with data from 15 stations and a later improvement included data from another 10 stations. The azimuthal coverage of these stations were limited to the first (Az = 2°-54°) and fourth (Az = 286°-344°) quadrant with respect to the epicenter and epicentral distances in the range of 8°-75°. Out of the 25 stations, 15 were Russian, 8 were CIS stations (Kirghizia 1, Kazakhstan 2, Turkmenistan 2 and Ukraine 3), 1 was in Norway (KONO) and 1 in Alaska, USA (COLA). A summary of the obtained parameters compared with those provided by the NEIC and CSEM is provided in Table 1.
Figure 2 shows the vertical broadband registrations of 11 of the above stations (Figure 3) which were obtained by the DPC in near real-time on March 25, 2002. The first motion polarities corroborate the Harvard centroid-moment tensor (CMT) solution. The north-north-west oriented nodal plane coincides roughly with the orientation of the aftershock sequence.
Figure 2. Registrations of the earthquake on March 25. Shown are the vertical components (BHZ) of 11 digital stations: BRVK is Borovoe, Kazakhstan (delta is 17°), ARU is Arti, Ural (21°), KIV is Kislovodsk, Caucasus (23°), TLY is Talaya, Baikal (29°), OBN is Obninsk, central European part of Russia (29°), PUL is Pulkovo, Northwestern Russia (35°), LVZ is Lovozero, Kola Peninsula Northwestern Russia (37°), TIXI is Tiksi, Northern Russia (47°), YSS is Yuzno-Sakhalinsk (54°), MA2 is Magadan (56°), BILL is Bilibino, Northeastern Russia (60°).
Figure 3. 12 Russian broadband stations that send the digital records in near real-time to Data Processing Center GS RAS in Obninsk.
Ns - Number of stations used in the location
I0 - Intensity
The March 25 earthquake was followed by more than 20 aftershocks with Mb > 4. The strongest aftershock was on April 12, 2002, with magnitude Mb = 5.6 (GS-RAS) and M0 = 1.5·1025 dyne-cm (from P-wave spectra of OBN) corresponding to MW = 6.1. This values are close to the values obtained by the NEIC, i.e. M0 = 1.2·1025 dyne-cm and MW = 6.0, and those by Harvard, M0 = 1.5·1025 dyne-cm and MW = 6.1.
The deep earthquakes of March 3, 2002The epicenters of the two earthquakes on March 3 were located 135 km northeast of the earthquake of March 25. Figure 4 shows the vertical broadband registrations of the same 11 digital station as shown in Figure 2.
Figure 4. Recordings of the earthquake of March 3, 2002. Shown are the vertical broadband components (BHZ) of the same stations as in Figure 2. See this figure for the station names and azimuthal distances
Analysis of the waveform data revealed phases (10-12 sec after the first arrival) that
cannot be identified. It is therefore assumed that we recorded two deep events with
a 10-12 sec difference in origin time and approximately the same location.
This was confirmed in a more detailed analysis. The foreshock was slightly more shallow,
i.e. 200 km depth, than the main shock, i.e. about 250 km. The parameters of both earthquakes
are listed in Table 2.
The depth estimation was made using the sP phases of the following stations: for the foreshock
ARU, TLY, OBN, LVZ, KONO, MA2, BILL and PET and for the main shock TLY, MA2 and BILL. At the other
stations the sP-phase interfered with the PP or PcP phase of the first event.
Ns - Number of stations used in the location
I0 - Intensity
The shallow earthquake of March 25The earthquake occured in the night between March 25 and 26 in the mountains of the highly seismic active region of Hindu Kush, 170 km North of the Afghanistan capital Kabul. Strong shaking was felt in Northern Afghanistan in the cities Kabul and Mazar-I-sharif and in Pakistan in Islamabad and Peshevar. In Dushanbe, Tajikistan, it was felt with intensity 3-4. Preliminary reports mention that about 2000 people were killed, nearly 4000 injured and more than 10,000 people became homeless due to this earthquake. Many people live in the streets, afraid to enter their house. Others live in or close to the desert without meals and water. The city Nahrin in the Baglan province was totally desolated and severe destructions has been observed in neighbouring Burka. The earthquake was followed by numerous aftershocks during the whole night. In the period between March 25 and 27 nine aftershocks with magnitudes 4 and higher are registered. These aftershocks raised the number of casualties.
The Afghan Government asked the World community for help. The United Nations sent humanitarian aid to the disastrous regions, including tents, blankets, food and medicine. Russia sent two airplanes with humanitarian cargo to Kabul.
The deep earthquakes of March 3This double earthquake occured in the mountains 240 km north-northeast of Kabul and was felt in many countries of Central Asia: Afghanistan, Pakistan, India, Tadzhikistan, Uzbekistan, Kyrgyzstan , Kazakhstan and Xinjiang, China. However, relatively little damage was reported as compared to the March 25 earthquake. Preliminary reports mention about 100 people killed in the Afghan province Samangan.
The data used in this paper are the data used for the Alert messages. This data set will be updated with time using data from other Russian and worldwide stations.