Patterns of Historical Earthquake Rupture in the Iranian Plateau

Patterns of Historical Earthquake Rupture in the Iranian Plateau 133the [ran-Turkey border, and (3) the Gowk-Sirch earthquakesin southern [ran. Other possible earthquake sequencesin which all magnitudes are M < 6 are not discussedhere.Rocks of the Talesh Mountains, the northwest continuationof the Alborz Mountains, have been thrust northeastwardand eastward over rocks of the south Caspian depression.An earthquake of Ms 6.0 in 1978 yielded a focalmechanism consistent with a low-angle thrust (Berberian,1983b; Fig. 8). To the west, the Sangavar fault consists ofnorthwest-striking reverse fault segment and a NNE-strikinghigh-angle fault segment that ruptured in two earthquakes.The first earthquake, of M -- 6.1, ruptured the northern partof the NNE-striking segment in 1863. The second earthquakeof M - 6.7 ruptured the southern part of this segment32 yr later, in 1896 (Fig. 8). This larger earthquake did notcontinue south into the reverse-fault segment (Berberian,1983b, 1995b, 1997; Berberian et al., 1992).Farther west, in the direction of Turkey, the 1844.05.13(I ~ IX, M -- 6.9), the 1879.03.22 (I ~ VIII, M -- 6.7),the 1883.05.03 (I ~ VIII, M ~ 6.2) earthquakes comprisesequence separated by 34 and 4 yr, respectively (Fig. 8).Available macroseismic data are insufficient to assign theseearthquakes to specific faults, although the 1879 event mayhave ruptured the South Bozqush fault.The Kelissa Kandi-Shadlu-Pambukh right-lateral strikeslipfault on the Iran-Turkey border sustained an earthquakeofM ~ 7.4 on 1840.07.02 (Fig. 9). Less than 3 yr later, theKhoy earthquake of M ~ 5.9 ruptured the Kamar Kassanfault (Fig. 9; Berberian, 1997). The meizoseismal zonesthese two earthquakes are separated by a gap more than 60km long that contains right-lateral strike-slip faults, includingthe Badalan fault. The 1319 St. Thaddeus earthquake(quoted earlier) might have ruptured this gap; however, sufficientdata are not available. West of the gap, the Chalderanright-lateral strike-slip fault in Turkey ruptured in1976.07.02 with an earthquake ofM s 7.1 (Arpat et al., 1977),280 yr after an earthquake on 1696.04.14 A.D. of M ~ 7.0in the same region, but not necessarily on the same fault.South of the Tabas thrust and Shotori range, a rightlateralstrike-slip fault zone, principally known as the Nayband/Gowkfault, extends south for more than 400 km. Mostof this fault zone has not sustained large-magnitude historicalearthquakes, but in its southern half, two earthquakesoccurred close together in space and time (Fig. 6).1981.06.11, the Gowk fault ruptured in an oblique strikeslipand reverse-slip earthquake with M s 6.7 (Berberian etal., 1984). Less than 2 months later, the Sirch earthquake ofMs 7.1 occurred on 28 July with a reverse-fault focal mechanism.This earthquake occurred where the Nayband-Gowkfault turns to the SSE into a zone of reverse faults (Fig. 10).The two meizoseismal zones are separated by the Zamanabadgap, 7 km long, which did not rupture. Smaller earthquakesstruck the meizoseismal zone of the 1981.07.28earthquake in 1877 (M 5.0), 1909 (M not established),(M 5.6), 1948 (M 5.9), 1969 (m 5.2), and (M s 6.9).:::44~00°E" " " ’ TURKEY!~Okm~TURKEYIRAN4/,.30OE" ’\/~ ""~.. ARMENIA/ \//"¯ .~.~ JAZERBAIJAN/ IRAN/1319.00.00(>5.3)°S.Thaddeus,~ _39.00°N-Figure9. Meizoseismal areas of earthquakesalong active faults in northwest Iran and adjacent Turkeymodified from Berberian (1997). Symbolsameas preceding figure.Noninteractive Large-Magnitude Earthquakes"I have visited most of the regions that are famous fortheir frequent occurrences of great earthquakes; amongthem are the district of Siraf [the present Taheri port]on the Persian Gulf situated between the mountains andthe sea; Saimareh in the Mehrjan Qozaq [MehrganKadeh = Saimareh and Dareh Shahr in the westernZagros] and Masbazan district [Mehrgan Qozaq +Masbazan = Ilam in the western Zagros] of Jebal[’Mountain’ in Arabic: referring to the Jebal province/Eraq-e-AjarrdMedia/Mada, the territory of the MedianTribes] at the foot of Mount Kabr [Kabir Kuh in Zagros];and the city of Antakiyeh [Antioch] in the Qonsorindistrict; and ’Avasem of Sham [Syria] at the mountainfoot; and velayat of Qumes [Kumes/Damghandistrict in northern [ran] which is highly seismic, theearthquakes are so violent that the springs dry up andgush out in another place. It is a very disturbed city ....and Amol is another earthquake-prone city which I visited;it is on the foot of the big Mount Damavand, andit is said that Damavand [in Alborz Mts] is the highestmountain in the world!" (Mas’udi, 943).The 1493.01.10 Nauzad earthquake of M -- 7.0 (withsurface rupture witnessed by Esfezari, 1493) and the 1838Nosratabad earthquake of M - 7.0 (with surface rupture)