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A geologic contribution to the evaluation of the seismic potential of the Kahrizak fault (Tehran, Iran)
Author(s)
Language
English
Obiettivo Specifico
3.2. Tettonica attiva
Status
Published
JCR Journal
N/A or not JCR
Peer review journal
Yes
Title of the book
Issue/vol(year)
1-4 / 287 (1998)
Publisher
Elsevier
Pages (printed)
187-199
Issued date
March 20, 1998
Abstract
In this paper we present the results of preliminary geomorphic and trenching investigations along the Kahrizak fault.
This fault is located south of the highly populated metropolis of Tehran and represents one of the main structures in the area containing important seismic potential. The Kahrizak fault has a very clear expression at the surface where it forms a prominent 35-km-long, 15-m-high scarp on Holocene alluvial deposits. The fault strikes N70°-80°W and dips to the north. Movement is prevalently right-lateral with the northern side of the fault up. Trench excavations exposed a sequence of weathered, massive, alluvial deposits which are dated, by means of radiometric methods, to the Holocene. In the trenches the sequence is intensely deformed by north-dipping, high- and low-angle faults within a 30-m-wide zone. On the basis of stratigraphic and structural relations, some evidence for individual Holocene earthquakes is found; however, we were not able to reconstruct the seismic history of the fault nor to evaluate the size of deformation produced by each event. Because of the possible ~10 m offset of ancient linear hydraulic artifacts (qanáts), that cross the fault, we hypothesize that the most recent event may have occurred in historical times (more recent than 5000 yr B.P.) and it may be one of those reported in
this area by the current catalogues of seismicity. Based on these preliminary investigations we estimate an elapsed time
between 5000 and 800 years, a maximum slip per event dmax of ~10 m, a minimum Holocene vertical slip rate of ~1 mm/yr versus a horizontal slip rate of ~3.5 mm/yr, a maximum of ~3000 years for the average recurrence time, and an expected Mw = 7.0 to 7.4. These can be considered as a first-hand reference for the activity on this fault.
This fault is located south of the highly populated metropolis of Tehran and represents one of the main structures in the area containing important seismic potential. The Kahrizak fault has a very clear expression at the surface where it forms a prominent 35-km-long, 15-m-high scarp on Holocene alluvial deposits. The fault strikes N70°-80°W and dips to the north. Movement is prevalently right-lateral with the northern side of the fault up. Trench excavations exposed a sequence of weathered, massive, alluvial deposits which are dated, by means of radiometric methods, to the Holocene. In the trenches the sequence is intensely deformed by north-dipping, high- and low-angle faults within a 30-m-wide zone. On the basis of stratigraphic and structural relations, some evidence for individual Holocene earthquakes is found; however, we were not able to reconstruct the seismic history of the fault nor to evaluate the size of deformation produced by each event. Because of the possible ~10 m offset of ancient linear hydraulic artifacts (qanáts), that cross the fault, we hypothesize that the most recent event may have occurred in historical times (more recent than 5000 yr B.P.) and it may be one of those reported in
this area by the current catalogues of seismicity. Based on these preliminary investigations we estimate an elapsed time
between 5000 and 800 years, a maximum slip per event dmax of ~10 m, a minimum Holocene vertical slip rate of ~1 mm/yr versus a horizontal slip rate of ~3.5 mm/yr, a maximum of ~3000 years for the average recurrence time, and an expected Mw = 7.0 to 7.4. These can be considered as a first-hand reference for the activity on this fault.
References
Ambraseys, N.N., 1963. The Buyin-Zara (Iran) earthquake of
September 1, 1962: a field report. Bull. Seismol. Soc. Am. 53,
705-140.
Ambraseys, N.N., Melville, C.P., 1982. A History of Persian
Earthquakes. Cambridge University Press, Cambridge, 219 pp.
Berberian, M., 1983. The Southern Caspian: a compressional
depression floored by a trapped, modified oceanic crust. Can.
J. Earth Sci. 20, 163-183.
Berberian, M., 1994. Natural Hazards and the First Earthquake
Catalogue of Iran, Vol. I. Historical Hazards in Iran Prior to
1900. International Institute of Earthquake Engineering and
Seismology (IIEES), Tehran, 603 pp.
Berberian, M., King, G.C.P., 1981. Towards a paleogeography
and tectonic evolution of Iran. Can. J. Earth Sci. 18, 210-265.
Berberian, M., Qorashi, M., Arzhang-Ravesh, B., Mohajer-Ashjai,
A., 1983. Recent tectonics, seismotectonics and earthquake-
fault hazard study in the Greater Tehran region, Geol.
Surv. Iran Rep. 56, 130 pp. (in Farsi).
Berberian, M., Qorashi, M., Jackson, J.A., Priestley, K., Wallace,
T., 1992. The Rudbar-Tarom earthquake of 20 June 1990 in
NW Persia: preliminary field and seismological observations,
and its tectonic significance. Bull. Seismol. Soc. Am. 82.
1726-1755.
De Mets, C., Gordon, R.G., Argus, D.F., Stein, S., 1990. Current
plate motions. Geophys. J. Int. 101, 425-478.
Goudie, AS., 1982. Calcrete. In: Goudie, A.S., Pye, K. (Eds.),
Chemical Sediments and Geomorphology, Precipitates and
Residua in the Near-Surface Environment. Academic Press,
London, pp. 93-131.
Hanks, T.C., Kanamori, H., 1979. A moment-magnitude scale. J.
Geophys. Res. 84, 2348-2350.
Jackson, J.A., McKenzie, D.P., 1984. Active tectonics of the
Alpine-Himalayan belt between western Turkey and Pakistan.
Geophys. J.R. Astron. Soc. 77, 185-264.
Jackson, J.A., Haines, J., Holt, W., 1995. The accommodation
of Arabia-Eurasia plate convergence in Iran. J. Geophys. Res.
100, 15205-15219.
Pedrami, M., 1981. Pasadenian Orogeny and the geology of
700,000 years ago in Iran. Internal Report Geological Survey
of Iran, 355 (in Farsi).
Priestley, K., Baker, C., Jackson, J.A., 1994. Implications of
earthquake focal mechanism data for the active tectonics of
the south Caspian Basin and surrounding regions. Geophys. J.
Int. 118, 111-141.
Shoja-Taheri, J., Niazi, M., 1981. Seismicity of the Iranian
plateau and bordering regions. Bull. Seismol. Soc. Am. 71,
477-489.
Stocklin, J., 1968. Structural history and tectonics of Iran: a
review. Bull. Am. Assoc. Pet. Geol. 7, 1229-1258.
Tchalenko, J.S., Iranmanesh, M.H., Mohajer-Ashjai, A., 1972.
The Babol-Kenar (1971) earthquake and the seismotectonics
of the Central Alborz (Iran). Ann. Geofis. 25, 27-36.
Wells, D.L., Coppersmith, K.J., 1994. New empirical relationships
among Magnitude, rupture length, rupture width, rupture
area, and surface displacement. Bull. Seismol. Soc. Am. 84,
974- 1002.
September 1, 1962: a field report. Bull. Seismol. Soc. Am. 53,
705-140.
Ambraseys, N.N., Melville, C.P., 1982. A History of Persian
Earthquakes. Cambridge University Press, Cambridge, 219 pp.
Berberian, M., 1983. The Southern Caspian: a compressional
depression floored by a trapped, modified oceanic crust. Can.
J. Earth Sci. 20, 163-183.
Berberian, M., 1994. Natural Hazards and the First Earthquake
Catalogue of Iran, Vol. I. Historical Hazards in Iran Prior to
1900. International Institute of Earthquake Engineering and
Seismology (IIEES), Tehran, 603 pp.
Berberian, M., King, G.C.P., 1981. Towards a paleogeography
and tectonic evolution of Iran. Can. J. Earth Sci. 18, 210-265.
Berberian, M., Qorashi, M., Arzhang-Ravesh, B., Mohajer-Ashjai,
A., 1983. Recent tectonics, seismotectonics and earthquake-
fault hazard study in the Greater Tehran region, Geol.
Surv. Iran Rep. 56, 130 pp. (in Farsi).
Berberian, M., Qorashi, M., Jackson, J.A., Priestley, K., Wallace,
T., 1992. The Rudbar-Tarom earthquake of 20 June 1990 in
NW Persia: preliminary field and seismological observations,
and its tectonic significance. Bull. Seismol. Soc. Am. 82.
1726-1755.
De Mets, C., Gordon, R.G., Argus, D.F., Stein, S., 1990. Current
plate motions. Geophys. J. Int. 101, 425-478.
Goudie, AS., 1982. Calcrete. In: Goudie, A.S., Pye, K. (Eds.),
Chemical Sediments and Geomorphology, Precipitates and
Residua in the Near-Surface Environment. Academic Press,
London, pp. 93-131.
Hanks, T.C., Kanamori, H., 1979. A moment-magnitude scale. J.
Geophys. Res. 84, 2348-2350.
Jackson, J.A., McKenzie, D.P., 1984. Active tectonics of the
Alpine-Himalayan belt between western Turkey and Pakistan.
Geophys. J.R. Astron. Soc. 77, 185-264.
Jackson, J.A., Haines, J., Holt, W., 1995. The accommodation
of Arabia-Eurasia plate convergence in Iran. J. Geophys. Res.
100, 15205-15219.
Pedrami, M., 1981. Pasadenian Orogeny and the geology of
700,000 years ago in Iran. Internal Report Geological Survey
of Iran, 355 (in Farsi).
Priestley, K., Baker, C., Jackson, J.A., 1994. Implications of
earthquake focal mechanism data for the active tectonics of
the south Caspian Basin and surrounding regions. Geophys. J.
Int. 118, 111-141.
Shoja-Taheri, J., Niazi, M., 1981. Seismicity of the Iranian
plateau and bordering regions. Bull. Seismol. Soc. Am. 71,
477-489.
Stocklin, J., 1968. Structural history and tectonics of Iran: a
review. Bull. Am. Assoc. Pet. Geol. 7, 1229-1258.
Tchalenko, J.S., Iranmanesh, M.H., Mohajer-Ashjai, A., 1972.
The Babol-Kenar (1971) earthquake and the seismotectonics
of the Central Alborz (Iran). Ann. Geofis. 25, 27-36.
Wells, D.L., Coppersmith, K.J., 1994. New empirical relationships
among Magnitude, rupture length, rupture width, rupture
area, and surface displacement. Bull. Seismol. Soc. Am. 84,
974- 1002.
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