Document Type : Full length article
Faculty of Geographical Sciences and Planning, University of Isfahan . Cellphone
Physical Geography, Faculty of Geography Sciences &amp; Planning, University of Isfahan, Isfahan, Iran
Evaluation of Neotectonic activity in catchment developments
(Case study: southern Karkas mountain watersheds)
By studying, the geological structure, landforms topography, pattern of drainage network systems, indicators and geomorphological evidences of each region, the performance of Active tectonics can be evaluated. The Karkas Mountain is located in the east of Isfahan and the magmatic arc of Urmieh – Dokhtar between Sannandaj and Sirjan. The purpose of this study is to investigate, evaluate and estimate Neotectonic and its effect on morphology, behavior, formation and evolution of southern catchments of Karkas heights using geomorphic morphometric indices and its adaptation to geomorphological evidence in the region.
Materials and methods:
In this study, after studying and collecting library information, preparing the required data, in the ArcGIS software environment, the area of the basins south of Karkas Heights (10 catchments) was determined and their drainage network was extracted from DEM. Using Geomorphologic indexes to evaluate the amount and intensity of Active Tectonics in the area. This Geomorphologic Indicators are the Ratio of a Circle (Re), Bifurcation ratio (Rb), Basin form (FF), Geomorphic features of the Hypsometric integral (Hi), Basin Volume Area (V/A), The topographic symmetry Factor (T), River Length-Gradient (SL), River Sinuosity (S), Mountain Front Sinuosity (Smf), Basin shape ratio (Bs), Alluvial fan Area (Af), Alluvial fan Slope (Sf). Then using the relative active tectonic index (Iat), As a model and conceptual technique the amount of tectonic activity in catchments was calculated. Finally, the morphological evidence of active tectonics in the study area was examined. DEM 90-meter of the country is surveying organization, geological map 1: 100000, topographic map 1: 50000, IRS satellite images and Google inherit the data used in this study.
Result and discussion:
Each of the quantitative characteristics of catchment basins with specific values represents a form in the catchments. The relative active tectonic index (Iat) and Geomorphological Indices show that the area is very active. The Niazmargh, Soh, Safiabad were more active than other catchment. Existence of numerous faults that are part of the Qom-Zefrah fault system is one of the geomorphological evidences in the study area. Each of the catchments in the area is affected by one or more fault systems. Quaternary faults do not exist in all catchments of the region and are seen only in the catchments of Maravand, Absenjed, Robat, Panavand, niazmargh and the border between Safiabad catchment area and niazmargh and Panavand catchments. The valleys and canals of the rivers of Maravand, Niazmargh, Soh and Kalaharood are suitable with geological structure, tectonic activities, slopes and erosion processes have different shapes. Another geomorphological evidence in the study area is alluvial fan section. The old, semi-active and active alluvial fan can be seen in Soh area. In Kalahrood catchment, the traces of old alluvial fans have been largely destroyed and only a few parts of it have been left. Tilt of the alluvial fan and displacement of the main waterway on the alluvial fan are the other effects of tectonic movements in the region.
The course of rivers in the mountainous part, depending on the land structure or tectonic structure, has an almost east-west or northeast-southwest trend, but after leaving the mountain, under the influence of the northern part, it turns to the south and goes north-south.
Some rivers (Soh, Kalahrood and Robat) have been diverted to the east due to the more uplifted of the northwestern part.
In the northwestern part, due to more uplift, successive alluvial fans have been formed, while in the south-eastern part no evidence of it is observed.
The slope of basins and rivers in the northwestern part is more than twice their slope in the southeastern part, which can be affected by tectonic movements. The average slope of the basins in the northwestern part is 25 percent and in the southeastern part is 12.7 percent and the average slope of rivers in the northwestern part is 20.75 and in the southeastern part is 8.1 percent.
In the northwestern part, the erosion power of rivers has increased so that rivers have been able to create deeper valleys (Soh and Kalahrood valleys). While in the southeastern part, the width of the valleys is usually greater than their depth. Vf is 1.7 in the northwestern part and 8 in the southeastern.
The heights of Karkas and its surroundings are active in terms of seismicity, so that in the last three hundred years, about six earthquakes of more than 4 Richter were recorded, the last of which occurred in 2016 in the Habibabad basin. During a four-year period (2008-2004), 1250 earthquakes have been recorded in Isfahan seismic network (Kalahrood, Zefreh, Nain, Qarneh and Pirpir stations)). The seismicity of Qom-Zefreh fault is estimated to be about seven Richter.According to the values of geomorphic indicators and seismic data it seems that the region is tectonically active and this activity has been more intense in Maravand, Niazmargh, Soh and Kalahrood basins. The intensity of tectonic activities decreases from northwest to southeast, so the region can be divided into northwestern and southeastern in terms of activity intensity.
The relative active tectonic index (Iat) and Geomorphic Indices show that the area is very active. The Niazmargh, Soh, Safiabad were more active than other catchment. The Iat index of catchments is 1.93 which varies from 1.2 to 2.6 in catchments. The deep River valleys (Soh, Kalahrood, Niazmorgh and Panavand), consecutive and fragmented alluvial fan (Soh and Kalahrood rivers), river terraces, diversion paths and riverbeds (Soh, Ka lahrood and Robat) and numerous faults are geomorphological evidence that confirm the characteristics of the basins are affected by tectonic movements in the region.
The results of geomorphological indices and seismic data of the region show that the catchments are active in terms of tectonic activity, but the intensity of tectonic activity in the region is not the same and its amount decreases from northwest to southeast. The impact of tectonic activity in the northwestern basins has been greater than its impact in the southeast. These activities have deepened valleys, changed the course and bed, increased the slope of some rivers, increased the erosive power and fragmentation and sequencing of alluvial fans.
Keywords: Watershed, geomorphological indexes Neotectonic, Karkas.