Document Type : Original Research Paper

Authors

1 Islamic Azad University (IAU), Science and Research Branch, Tehran, Iran

2 Islamic Azad University (IAU), North Tehran Branch, Tehran, Iran Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran

Abstract

The paper presents a method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results from the analysis are accumulated and expressed as an index of relative active tectonics (Iat), which divided into four classes from relatively low to highest tectonic activity. The study area along the south flank of the central Alborz mountain range in north Iran is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. The recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Alborz mountain range. Geomorphic indices indicate the presence of differential uplifting in the geological past. The high class values (low tectonic activity) for Iat mainly occur in the south and southeast of the Karaj drainage basin, while the rest of the study area has classes of Iat suggesting moderate to high tectonic activity. Around the Amirkabir Lake, Iat has the highest value. The distribution of the indices defines areas associated with different mountain fronts and estimates of relative rates of tectonic activity. More than half of the study area is classified into classes 2 or 1 of high to very high tectonic activity in terms of the apparent geomorphic response. In different tectonic environments with greater rates of active tectonics, the values of indices would differ as well as their range in value. The stream network asymmetry (T) was also studied using morphometric measures of Transverse Topographic Symmetry. Analysis of the drainage basin and a number of sub-basins in the study area results in a field of T-vectors that defines anomalous zones of the basin asymmetry. We test the hypothesis that areas with great stream migration are associated with indicatives values of Iat.
 

Keywords

 
References
Allen, M. B., Alsop, G. I., Zhemchuzhnikov, V. G., 2001- Dome and basin refolding and transpressive inversion along the Karatau Fault System, Southern Kazakstan. Journal of the Geological Society 158, 83–95.
Allen, M. B., Ghassemi, M. R., Shahrabi, M., Qorashi, M., 2003- Accommodation of Late Cenozoic oblique shortening in the Alborz Range, Northern Iran. Journal of Structural Geology 25 (5), 659–672.
Ashtari, M., Hatzfeld, D., Kamalian, N., 2005- Microseismicity in the region of Tehran. Tectonophysics 395, 193–208.
Azor, A., Keller, E. A., Yeats, R. S., 2002- Geomorphic indicators of active fold growth: South Mountain-Oak Ridge Ventura basin, southern California. Geological Society of America Bulletin 114, 745-753.
Berberian, M., Yeatz, R. S., 2001- Contribution of archeological data to studies of earthquake history in the Iranian Plateau. Journal of Structural Geology 23, 563-584.
Bull, W. B., 1978- Geomorphic Tectonic Classes of the South Front of the San Gabriel Mountains, California. U.S. Geological Survey Contract Report, 14-08-001-G-394, Office of Earthquakes, Volcanoes and Engineering, Menlo Park, CA.
 Bull, W. B., McFadden, L. D., 1977- Tectonic geomorphology north and south of the Garlock fault, California. In: Doehring, D. O (eds), Geomorphology in Arid Regions. Proceedings of the Eighth Annual Geomorphology Symposium. State University of New York, Binghamton, pp. 115-138.
Cannon, P. J., 1976- Generation of explicit parameters for a quantitative geomorphic study of Mill Creek drainage basin. Oklahoma Gelogy Notes 36(1), 3-16.
Ehteshami Moinabadi, M., Yassaghi, A., 2006- Geometry and kinematics of the Mosha Fault, south central Alborz Range, Iran, An example of base ment involved thrusting. Journal of Asian Earth Sciences 2, 928-938.
EL Hamdouni, R., Irigaray, C., Fernandez, T., Chacon, J., Keller, E. A., 2007- Assessment of relative active tectonics, southwest border of the Sierra Nevada (southern Spain). Geomorphology. Article in press.
Gelogical Survey of Iran, 1977- Aeromagnetic map of Tehran, Gelogical Survey of Iran, Tehran, Scale 1:250000.
Hack, J. T., 1973- Stream-profiles analysis and stream-gradient index. Journal of Research of the U.S. Geological Survey 1 (4), 421-429.
Hare, P. H., Gardner, T. W. M., 1985- Geomorphic indicators of vertical neotectonism along converging plate margins, Nicoya Peninsula, Costa Rica, In Tectonic Geomorphology, Morisawa, M, Hach, J. T (eds). Allen and Unwin, Boston, 75-104.
Hayakawa, Y., Takashi, O., 2006- DEM-based identification of fluvial knickzones and its application to Japanese mountain rivers. Geomorphology, 78, 90-106.
Keller, E. A., 1986- Investigation of active tectonics: use of surficial Earth processes. In: Wallace, R.E. (Ed), Active tectonics, Studies in Gephysics. National Academy Press, Washington, DC, pp. 136-147.
Keller, E. A., Pinter, N., 2002- Active tectonics, Earthquakes, Uplift and Landscape. Prentice Hall: New Jersy.
Mayer, L., 1990- Introduction to Quantitative Geomorphology. Prentice Hall, Englewood, Cliffs, NJ.
Molin, P., Pazzaglia, F. J., Dramis, F., 2004- Geomorphic expression of active tectonics in a rapidly-deforming forearc, sila massif, Calabria, southern Italy. American Journal of Science 304, 559-589.
Nazari, H., 2005- Seismotectonic map of the central Alborz. Gelogical Survey of Iran, Seismotectonic Department, Scale 1:250000.
Pike, R. J., Wilson, S. E., 1971- Elevation-relief ratio, hypsometric integral and geomorphic area-altitude analysis. Geological Society of America Bulletin 82, 1079-1084.
Ramírez-Herrera, M. A., 1998- Geomorphic assessment of active tectonics in the Acambay Graben, Mexican volcanic belt. Earth Surface Processes and Landforms 23, 317-332.
Rockwell, T. K., Keller, E. A., Johnson, D. L., 1985- Tectonic geomorphology of alluvial fans and mountain fronts near Ventura, California. In: Morisawa, M. (Ed), Tectonic Geomorphology. Proceedings of the 15th Annual Geomorphology Symposium. Allen and Unwin Publishers, Boston, MA, pp. 183-207.
Salvany, J. M., 2004- Tilting neotectonics of the Guadiamar drainage basin, SW Spain. Earth Surface Processes and Landforms 29, 145-160.
Silva, P. G., 1994- Evolución geodinámica de la depresión del Guadalentín desde el Mioceno superior hasta la Actualidad: Neotectónica y geomorfología. Ph.D. Dissertation, Complutense University, Madrid.
Silva, P. G., Goy, J. L., Zazo, C., Bardajm, T., 2003- Fault generated mountain fronts in Southeast Spain: geomorphologic assessment of tectonic and earthquake activity. Geomorphology 250, 203-226.
Strahler, A. N., 1952- Hypsometric (area-altitude) analysis of erosional topography. Geological Society of America Bulletin 63, 1117-1142.
Yassaghi, A., Madanipour, S., 2008- Influence of a transverse basement fault on along-strike variations in the geometry of an inverted normal fault: case study of the Mosha Fault, Central Alborz Range, Iran, Journal of Structural Geology, doi: 10.1016/j.jsg.2008.08.006.