Patterns of Historical Earthquake Rupture in the Iranian Plateau

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Patterns of Historical Earthquake Rupture in the Iranian Plateau 125tains to collide and tumble down; the debris of the collisionblocked the course of the rivers that ran between,and the waters of the rivers receded and formed a lake..." (ebn al-’Amid, 961, describing the 958.02.23Ruyan-Taleqan, northwest Tehran, earthquake of Io --IX, M -- 7.4; quoted by Biruni-Kharazmi, 1025).Active reverse faults of the Tehran region are parallelto the northwest-trending structural grain of the AlborzMountain belt (Fig. 3). The historical earthquake sequenceoccurred over a time period longer than 1100 yr, muchlonger than other case histories presented here. Four earthquakesof M > 7 devastated the Tehran region in a fourcenturyperiod from 743 to 1177, but only one earthquakethat large has struck in the last 800 yr, in 1830 (Ambraseys,1970; Ambraseys and Melville, 1982; Berberian et al., 1985;Berberian, 1995b; Fig. 3). At least three damaging historicalearthquakes ruptured adjacent segments of the Mosha faultfor a continuous distance of nearly 200 km: 958 (westernsegment), 1665 (eastern segment), and 1830 (central1830.03.27( IX.7.1 )-- ----I----I~------TEHRAN JAJRUD DAMAVAND1900-1800-- 1 200 1177--1119.12.10(Vl I I ,6.5)QAZV I N1177.05.00(IX,7.2)RAY1665.06-07 (V I I, 6.5) 1700?--~). ?DAMAVAND1600-1200-- I 000A.D.MAGNITUDE 6.0-6.9(Ms)958.02.23(X,7.7)S. 0-5.90 ? QUEST I ONABLE DAMAGERAY864.01-02(Vl I ,5.3)~ RAYB.C. --~[DISTANCE (km)]200 180 140 120 100 80 60 40 20 0 20L i t 1 l l l l__l__l__l"-" 1100-1000-~ 900 -743.03-06(~111+,7.2)800 -TSD 700 -A.D...,’312--280 BC(Xg;6)?40[60 80 100L~Figure 3. (Top) Meizoseismal areas of large-magnitude earthquakes striking theTehran metropolitan area (hatched). Symbols same as in Figures 1 and 2. Guidoboniand Traina (1995) dispute the location of the March to June 743 (exact date is unknown)earthquake and suggest that it is located in the Caspian Gates area of Derbent in Daghestan(750 km NW of Tehran, not shown in Fig. 1). (Bottom) Time-space diagram ofearthquakes in the Tehran area; symbols same as in Figure 2. Meizoseismal area of958 earthquake not well defined. Distances are along strike with respect to Tehran.
126 M. Berberian and R. S. Yeatsment, north of Tehran; Berberian et al., 1985). The Moshafault has a youthful scarp. The boundary between the 958and 1830 ruptures is marked by an abrupt change in faultstrike, but the boundary between the 1830 and 1665 rupturesis not marked by an obvious geological discontinuity. Thecontinuation of the Mosha fault east of the 1665 rupture hasnot ruptured historically in a large earthquake (Fig. 3; Berberianet al., 1985).We are unable to assign the 855 to 856 (exact year uncertain)and 1177 earthquakes to specific faults. These earthquakescould have ruptured the North Tehran thrust (NTT),which marks the range front at the north edge of the Tehranplain (Fig. 4). In contrast to the Mosha fault, however, theNTT has a less distinctive fault scarp. An additional complicationis the presence of south-dipping reverse faults, inpart blind, such as the Bagh-e-Feyz, Davudieh, T.V., Mahmudieh,Shian, and other faults in the Tehran plain (Fig. 4).South-dipping reverse faults may account for uplift of theNTT footwall block, analogous to the 1994 Northridge earthquakeon a blind thrust that uplifted the footwall of the SantaSusana fault (Yeats and Huftile, 1995). If this is the case,the south-dipping faults could have produced the 855 to 856and the 1177 events. If such an earthquake occurred today,it would wreak a catastrophe on the Tehran metropolitanregion. A complicating factor is the poor documentation ofthe location of the 855 to 856 earthquake, which could bethe mislocated Kumes earthquake (M-- 7.4 + ) of 856.12.22in the Damghan region (located in Fig. 1). These eventscould also have been located along the Ray-Kahrizak faultsystem south of Tehran (Figs. 1 and 3). The Qazvin earthquake(M-- 6.5) of 1119.12.10 on the North Qazvin thrustto the west may be a continuation of the zone of large earthquakeson the Mosha fault but separated from the surfacetrace of that fault by a historical gap (Fig. 3).Dasht-e-Bayaz/Abiz FaultsThe first two study regions are part of the reversefaultedranges that extend across northern Iran, including theAlborz Range (Fig. 1). To the southeast, across the centralKavir depression, the structural style changes dramatically~ulti0 0 0 0TehronFigure 4. Map of Tehran metropolitan areas of 1970 (diagonal dashed lines) showingNorth Tehran thrust, smaller faults, and partly covered faults (numbered by a letterfollowed by a number), some range facing within the Tehran plain. Contour intervalsin 200 m. Open circles indicate anomalies in groundwater elevation (dropping to thesouth). Long and short broken lines are the existing highways and roads, respectively,in Tehran.
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Patterns of Historical Earthquake Rupture in the Iranian Plateau

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