جستجوی مقالات مرتبط با کلیدواژه "شاخص های ریخت زمین ساختی" در نشریات گروه "جغرافیا"

The sensitivity of the drainage pattern to the active tectonics processes leads to a geomorphic expression that provides a useful tool to evaluate relative tectonic activity (Cox, 1994). Geomorphic indices provide a useful method for assessing the extent of tectonic activity; Especially in areas where earthquakes happen on faults in which there was not enough information in advance. The study area is in the west of Lut block, southeast of Iran, which is in the range of longitude from 55°22ˊ 15˝ to 58° 31ˊ17˝E and latitude from 28°50ˊ4˝ to 31°9ˊ30˝N. This region has a long history of devastating earthquakes, the historical types of which date back to around 1850AD. The occurrence of earthquakes on previously unknown faults (Bam, 2003) and the need to pay attention to areas in this part that have not yet experienced a devastating earthquake despite being surrounded by active faults (Kermen city), are the most important reasons that led us to find the best way of morphotectonic analysis and compare the results to seismic structures and data as a tool to identify structures and their activities also to estimate the seismic risk.

To obtain the drainage network layer, basins area, and water dividing layer in the study area, the hydrological modeling process was done by Arc GIS10.3 software. The basic data used are 30 m resolution DEM and geological maps. Also, to investigate the relationship between seismicity and tectonic activity, seismic data were used for earthquakes greater than 0.4 Mw. In this study, the results of calculating 7 geomorphic indices, including stream length-gradient index(SL), drainage basin asymmetry(Af), hypsometric integral(Hi), the ratio of valley-floor width to valley height(Vf), index of drainage basin shape(Bs), index of mountain front sinuosity(Smf), and Transverse Topographic Symmetry Factor(T), for 51 basins were analyzed by Iat and AHP methods. Finally, by using seismic data and field studies, we discuss our findings to compare the accuracy of AHP and Iat methods in analyzing morphometric indices to assess seismic risk, which is the aim of this paper.

The evaluation of the distribution of relative tectonic activity in the study area according to Iat, which is obtained by averaging the different classes of morphotectonic indices, divided the region into three categories in terms of tectonic activity. Class2, class3 and class4, have allocated 5.9%, 54.9%, and 39.2% of the total study area to themselves, respectively. It should be noted that none of the basins were in class1. 43.2% of epicenters were located in basins with high activity and 17.6% in low ones. Since the Iat index is not based on the weighting of the indices, all the indices were calculated with equal importance ratios. Therefore, there are some inconsistencies in comparing the Iat distribution map with the main structures of the region and the epicenter of the earthquakes. The AHP makes it possible to determine the amount of tectonic activity in the study area base on the weight and importance of each index compared to others, instead of relying solely on the average of each index (Iat). The values of the coefficient of determination(R2) are extracted from the graph of the indicators relative to each other. The correlation coefficient(R) was calculated from the roots of R2. After checking the acceptability of the Inconsistency, the final weights assigned to each of the indicators are (0.015)Bs, (0.012)Smf, (0.025)AF, (0.021)T, (0.104)Hi, (0.116)Vf, (0.708)SL. These results were classified into four categories. Accordingly, class1, class2, class3 and class4, occupy 21%, 24%, 31%, 24% of the total study area, in turn. The basins with very high and high tectonic activity, are all located along the main faults of the region, in addition, the distribution of earthquakes in these basins (81.8.% of earthquakes were in high active basins and 4.4% in low ones), shows how they are consistent with the results of AHP.

In this study, we tried to more accurately assess the impact of active tectonics and determine the most appropriate method for analyzing geomorphic indices, by comparing the results obtained from Iat and AHP methods. Proper matching of geomorphic features, calculated indices, and classification of relative tectonic activity obtained by the AHP, with the main structures, field observations, seismic data and previous studies in the study area, confirms the significant superiority and higher accuracy of AHP over the Iat in the identification of tectonically active areas which subsequently leads us to seismic hazard assessment. Based on the final map derived from the AHP, the study area was divided into four tectonic activity classes. The results show that morphological features in the study area are strongly affected by the main faults. The basins along them, generally show very high to high tectonic activity rates. The existence of many active faults, the epicenter of earthquakes and the location of most cities in the study area within or adjacent to basins with very high to moderate tectonic activity indicate the need for attention and additional studies there.The findings of this paper show how using a suitable way of morphometric analysis can help us to identify areas with the potential for seismic hazards. Due to its low-cost and timesaving, this method can be a good alternative for expensive and complex methods, especially in vast and remote places. As a result, it can be a useful tool for regional planners and decision-makers involved in seismic risk assessment and disaster risk reduction.

Morphological study of ​​Tabriz north fault indicates the high rate of tectonic activity along this fault. The indices calculated for Tabriz north fault confirms this fault’s activity aswell. Tabriz fault with approximate length of 97 km has formed of two main parts ( the northern part and the southern part ) . The changes of geomorphologic indices value along Tabriz north fault show difference in the behavior of this fault along itself. This difference of behavior impacts on geomorphologic behavior of this fault’s surrounding areas and creates different landscapes along this fault and also at its north and west part. Based on the difference in behavior of Tabriz north fault, it is separable in to three parts.
So that, at the northern part of Tabriz north fault, a gentle up rise and tectonic activities at the northern block of this fault and lack of tectonic activities and up rise at its southern block can be observed. The southern part of this fault also shows different behavior along itself, i.e. at a length of southern part of the fault which extends from north of Tabriz airport up to the south part of Baghmishe town. At the northern block of Tabriz fault, a gentle rate of up rise and tectonic activities is observed.
While, at a length of the southern part of the fault which extends from Baghmishe town up to Bostan abad town, we observe tectonic activities and up rising at the south block of this fault and low rate of up rising and tectonic activities at the its northern block.

In the present age the parts of the earth's crust have tectonic movements and in the future will be more prone to risk. Geomorphological processes and also forms is very sensitive to the tectonic activity and changes by this motion. The assessment of tectonic activity using by some indicators have a major role in identifying these activities and helps to interpret the tectonic regions. Research In this study for the determination of tectonic activity in Frahzad basin in the north western of metropolitan Tehran, using and calculating geomorphic indices such as Stream length gradient index (Sl), Valley floorvalley height ratio (Vf), Asymmetric factor (Af), Topographic inversion symmetry (T), Drainage basin shape ratio (Bs), and meandering rivers (S). The research procedure is based on analytical method. The Physical and conceptual tools of this research are the topography and geology maps of the study area, satellite images and GIS software, in the form of ARC GIS 10 and several field visits from landforms, has been used. Discussion and This basin, with an area equivalent to 35,8 kilometers, one of the subbasins of the mountain range north of the Tehran metropolis, according to range of processes (mainly sliding and falling), is suitable for the assessment of relative tectonic activity. The results indicate that the farahzad basin based on indicators of the Sl, Vf, Af, T and S in active status and Semi-active status is measured according Bs. Analysis of these quantities represent the activity of the basin in the present age and the average tectonic activity based on IAT index (Index of relative active tectonics) puts this basin in the class 1. The results correspond with the geomorphological evidence (landslide occurrence).