Tabas Earthquake of 16 September 1978, Mw=7.4

Tabas Earthquake of 16 September 1978, Mw=7.4

Ten years after the 1968 Dasht-e Bayaz/Ferdows earthquakes, the seismicity seems to have migrated cross fault from the Ferdows thrust in the northeast to the Tabas thrust fault in the southwest. The 1978 earthquake with Magnitude of Mw=7.4 killed more than 15,000 people, destroyed or severely damaged about 90 villages, partially damaged another 50 villages in the region, and completely demolished the evergreen oasis town of Tabas-e Golshan, where 85% of the inhabitants (11,000 out of 13,000) were killed. The earthquake ruptured the unmapped and unknown Tabas thrust fault at the western Neogene foothills of the Shotori Mountains. Evidence of active faulting is preserved in the landscape in the form of truncated asymmetric anticlinal folding in the Neogene molase deposits, deformation of the late Quaternary alluvial fan deposits, and widespread river incision. The Tabas-e Golshan earthquake was associated with (i) 75-km long, coseismic surface thrust faulting dipping east–northeast along a curved fault line and (ii) flexural-slip faulting in the form of bedding-plane slip with a thrust mechanism on the hanging wall of the Tabas thrust in a vast area. About 75 km of discontinuous coseismic thrust faulting, in several segments of arcuate form, was mapped at the surface along an existing but unrecognized foothill-front reverse fault, the Tabas active thrust. The highest-quality, locally recorded aftershock hypocenters occurred mainly at a depth less than 23 km with a high concentration of seismic activity between 8 and 14 km. The best-located aftershocks with their well-constrained focal mechanisms demonstrated an active imbricate listric thrust system (covering both the hanging wall as well as the footwall blocks) with fault planes flattening into a possible basement decollement zone. Analyses of strong motion records indicated that the rupture propagation was mostly unilateral from the southeast to the northwest at an average rupture velocity of 2.5 km/s. The majority of the slip, in at least four subevents, contributing to the strong-motion signals and the WWSSN body waves, terminated about 15 km NW of Tabas-e Golshan, giving a fault length of 90 km. Maximum coseismic surface faulting of about 75 km was observed and mapped on the surface. As with the teleseismic location, the relocated epicenter of the 1978 Tabas-e Golshan mainshock is placed close to the southern end of the coseismic surface ruptures, indicating a possible unilateral northward rupture propagation. Analysis of strong-motion records indicates the presence of at least four, and probably more, discrete subevents in the mainshock, but their locations could not be constrained. Since the maximum measured “single” thrust displacement at the surface was only 35 cm, the major part of the primary rupture is likely to have been blind. Aftershock locations from the deployment of nine local seismometers showed that (i) most of the aftershocks were located in the hangingwall of the Tabas thrust; (ii) the seismicity flattened with depth toward east northeast; (iii) aftershocks concentrated in depth about 10 km; (iv) scattered seismicity located in the Tabas playa (on the footwall) indicating fault activity to the west of the surface rupture as well; and (v) very little activity was detected beneath the Shotori Mountains to the east, where the range-front fault did not show any surface activity (Berberian, 2014).

 

 

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Nesa-Atrak Earthquake of 20 August 943, Ms.7.6

Nesa-Atrak Earthquake of 20 August 943, Ms.7.6

In August 20, 943, a catastrophic earthquake in the districts of Nesa destroyed many villages, killing more than 5000 people. The Nesa-Atrak earthquake of August 943 with Ms=7.6 occurred due to the activity of Ashkhaneh fault (eastern segment of  Takal Kuh).

Nahavand (Firuzabad) Earthquake of 16 August 1958 Mw.6.6

Nahavand (Firuzabad) Earthquake of 16 August 1958 Mw.6.6

During this earthquake sequence, about 170 villages were destroyed or damaged, more than 130 people were killed, and more than 200 people were injured in the Nahavand area. After the 13 December 1957 Farsinaj earthquake and its aftershocks, the 16 August 1958 Mw 6.6 earthquake, preceded by two strong and damaging shocks of 14 August 1958 [11:27 UTC, Ms 5.7; and 15:26 UTC, Ms 5.5] took place on the Zagros Main Recent fault to the southeast of the 1957 earthquake. The timing and overlap of the meizoseismal areas of the 1957 and 1958 earthquakes indicate temporal clustering and loading of the adjacent fault segments, with the earthquake sequence propagating to the southeast. The 1957 and the 1958 events were part of the earthquake sequence that began on 23 January 1909 Mw7.4 Silakhor earthquake along the Zagros Main Recent fault (Berberian and Yeats, 2001). Unfortunately, the meizoseismal areas of the three 1958 earthquakes, as well as the ground deformations associated with them, were not documented immediately afterward. Furthermore, teleseismic data with large location errors cannot be used to separate the areas of the three 1958 events. All the reports address the accumulated impacts of the damaging events as foreshocks and the mainshock (Montandon, 1957; Hagiwara and Naito, 1959; Rothe, 1969; Nabavi, 1972; Ambraseys and Moinfar, 1974; Tchalenko and Braud, 1974). Based on information provided by local villagers in 1971 (Tchalenko and Braud, 1974) and 1973 (Ambraseys and Moinfar, 1974), both authors reported three sets of surface faulting, as follows (two sets by the former and three sets by the latter):

  • SE of Larehkuh [Cheshmeh Mahi to Givaki] in the SW: This is a NW–SE trending ground fracture of 15-km long with maximum vertical displacement of 2 m (southeastern side downthrown). The southeastern part of the reported faulting coincides with the Garrin fault segment, and the northwestern part of the reported fault is along the southeastern part of the Sahneh fault segment of the Zagros Main Recent fault.
  • NE of Larehkuh [Firuzabad; Barreh Farakh to Kariz and Leylan] in the NE: On either side of Firuzabad, a 20-km-long NW–SE trending surface rupture with southwestern block downthrown by a few tens of centimeters was developed. This surface rupture coincides with the Nahavand segment of the Zagros Main Recent fault.
  • SW of larehkuh [Dehkohneh–Kaladeh] in the SW: A NW–SE ground rupture about 8 km long with the northeast block downthrown. The ground rupture is located along the southeastern part of the Sahneh segment of the Main Recent fault (Figure 12.12).

It seems that the Nahavand-Kahriz, Garrin, and southern tip of the Sahneh segments of the Zagros Main Recent fault were reactivated during the 1958 three-earthquake sequence (Berberian, 2014).

Berberian, 2014_Page_284

Mazandaran-Gilan Earthquake of 15 August 1485, Mw.7.2

Mazandaran-Gilan Earthquake of 15 August 1485, Mw.7.2

Just before sunset on Sunday 15 August 1485, there was a catastrophic earthquake in Gilan, particularly affecting Dailamistan, a large area between Gilan and Mazandaran to the east. In Tunekabun the shock demolished sbstantial buildings such as castles, mosques, shrines and hamams and what was felt was damages beyond repair. In Gurhiyan and Gulijan damage was equally severe, with the causalities, and a strong castle in the region was levelled with the ground. Also in Shakur many villages were ruined and old buildings were destroyed, with causalities. Further to the south, in Rudbarat, many people perished, but the number is not known exactly. In Taliqan other castles were ruined and at Palisan the fort collapsed completely, killing 78 of its inhabitants. Throughout Dailamistan the shock triggered rockfalls from the mountains and many animals perished. To the northwest, in Dailaman, many old buildings collapsed but the inhabitants and the local ruler, who was at prayers, escaped. Part of the palace at Rankuh fell down, but further to the north and northwest, at Lahijan, Gukeh, Kaisum, Pashija and Lashtinshah, there was little damage and no one was killed, although the shock was strongly felt in these areas. Aftershocks continued for six weeks until the end of Ramadan, or early October, keeping the survivors camping out in the open. However, another strong aftershock occurred on Monday 3 July 1486, but it was not as destructive as the mainshock.

Deylam EQ (En)