Bamiyan buddhas and Band-e-Amir phytoherms lakes under the Hindu Kush sismicity influence : The E-W herat fault versus N-S 50 km deep moho isopach line

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Bourrouilh-Le Jan, Francoise
Holding Date 16 September 2008

Located SW of the Hindu Kush range, Bamiyan city, with its Buddha statues, and the Band-e-Amir lakes, with colourfull bioherm terraces are well known. The Bamiyan Giant Buddhas had been carved out into a relatively soft mud-supported conglomerate of Miocene age, deposited inside an intra-mountaneous basin. The smooth oriented E-W carved cliff is also cut by fine perpendicular linear small fissures which have been enlarged by the past explosions. As for the lakes, their presence is due to the chemical and biologically induced building-up of semicircular or successive linear travertine dams. The discovery of a highly truncated karstic network located at an elevation of around 4,000 m, along the base of Maastrichtian carbonate cliffs surrounding the lakes, could explain the presence of this carbonate sedimentation which has fluctuated with time. Despite Bamiyan Buddhas and the Band-e-Amir lakes are localised at the eastern end of the Herat major fault, they are both under the influence of intense seismic activity of the Hindu Kush.
The Hindu Kush concentrates most of seismic activity of Afghanistan, with the highest number of earthquakes and of the largest magnitudes. It represents the postulated final stage of subduction of oceanic lithosphere along the collisional boundary between India and Eurasia and to the northern drift of the Afghan Gondwanian block towards the Eurasiatic plate.
Heuckroth and Karim (1973) synthetised the seismicity of Afghanistan from 1893 to 1969. The Herat fault activity is historically known by the destruction of numerous Afghan monuments. This earthquake list has been completed by data from the USGS National Earthquake Center and the I.P.G. in Strasbourg (France) for the area between longitude 67° to 70° East and latitude 34° to 36° North. The seismicity of the area from 1950 to the end of 2003, indicates that earthquakes are localised on both terminations of the Herat fault.
Between 1893 and 2003, the activity at Band-e-Amir and Bamyian still resulted in eight earthquakes with magnitudes from 7.3 down to 4.5. All these earthquakes are localised on a N-S trend line, roughly following the 67° 30’ meridian, appearing perpendicular to the two major faults of Herat and Andarab faults. Furthermore, this North South fault coincides with the N-S dotted line of the 50 km deep Moho isopach.
A high density network of faults is known NW of both areas, but has not yet been mapped in detail. So, no more precise details of the real fault involved in these earthquakes can be given, but the seismic activity is in direct relation with the Hindu Kush seismic activity and the 50 km N-S deep Moho isopach line. In conclusion, the E-W Herat fault is a surficial brittle fault, located in the fragile lithospheric zone whereas the 50 km N-S deep Moho isopach fracture zone, revealed by the Saygan earthquake and the bioherms dam described destructions, represents a deep ductile crustal fault, most probably related to the Owen transform fault system.