Document Type : پژوهشی
Authors
1 Ph.D. Student Hakim Sabzevari University, Sabzevar, Iran
2 Associate Professor at Hakim Sabzevari University, Sabzevar, Iran, - Professor of Hakim Sabzevari University, Sabzevar, Iran
3 Professor of Hakim Sabzevari University, Sabzevar, Iran
4 Assistant Professor of Hakim Sabzevari University, Sabzevar, Iran
Abstract
1- Introduction
Today, the phenomenon of land subsidence is one of the most important geomorphologic hazards on a global scale, causing a great deal of damage to urban and rural construction. According to the UNESCO definition, "subsidence is the collapse or land leveling that occurs due to different large and small scale causes" (Amir Ahmadi et al., 2013: 2). Pourkhosravani et al, (2012) Only with radar interferometer technique studied the geometry of duality, The results of this study showed that, firstly, citing excessive productivity of underground waters is not the main reason for the subsidence phenomenon; secondly, the phenomenon of subsidence in Iran's plains is the result of a duality in the crustal motions between the plains and adjacent mountains. In this research, the tectonic indexes and radar interferometry technique have been used with regard to the data and information available to detect the tectonic activity of the area.
2-Methodology
In order to investigate the state of activity of the newly tectonic area, topographic maps of 1: 50000 and 1: 10000 map of geology and radar images are used in the earthquake discussion from USGS US from 1923
to 2018. Also, to study the subsidence of the Joveyn area, the satellite Sentinel-1A satellite radar data for 2017 and 2018 was used in Canada and processed by SNAP software. The resources used in this research were based on library studies and surveys, topographic maps and radar images and field surveys.
3-Discussion and results and findings
The results of the used Indicators, earthquake zoning and radar interference are defined in the research as follows:
River Gradient Index) SL): This index was first presented by Hack (1973), in the study of the role of rock resistance on water flow in the Appalachian Mountains in the southeast of America as numerical values of the river gradient index Table1).
Table(1): River Gradient Index)SL)
High
ΔH(m)
ΔL(m)
Lsc(m)
Sl
Condition
1200-1300
100
14769
32050
217
low
1100-1200
100
15814
67170
424
medium
1000-1100
100
29798
122931
412
medium
-Asymmetric index(AF):
In this calculation, the obtained numbers (33.7) of the basin showed that the value of the index is less than 50. Therefore, we have the tectonic activity on the left side of the main stream and we face the subsidence phenomenon on the right.
-Reverse topographic symmetry index: (T)
to calculate this index in the Joveyn basin, a section has been created in each sub-area and its value has been calculated. According to (table 2), the index value in all three sub-basins is less than 1, indicating the asymmetry and active tectonics in the whole basin.
Table (2): Reverse topographic symmetry index
Route
Da(km)
Dd(km)
T
Condition
1
18/43
21/33
0/86
active
2
15/38
16/91
0/9
active
3
14/53
16/78
0/86
active
-Hypsometric and Hypsometric Integral Curves
In the hypsometry integral, the numerical value has a value of 0.5 in the range of young to adult topography.
Mountain Sinocity Index: (Smf)
Table (3): Mountain Sinocity Index
shape
LMF
LS
S
Condition
1
26/94
12/34
2/18
Semi active
2
41/86
11/85
3/5
Semi active
3
33/05
18/72
1/76
active
4
46/02
23/04
1/99
active
-Sinocity index of the river: (S)
According to the calculations, the index of the main bend and bend of the main river is less than 1. Which represents the new activities in the region.
-Valley Depth Wide Index (VF):
In passive regions, the average value of this indicator is usually higher than 7 in terms of over-rupture (Ranjbar Manesh, 2013).
Table(4): Valley Depth Wide Index
Condition
Vf
Vfw
Eld
Erd
Esc
number
active
1.3
629
2057
2110
1604
Figure 1
active
0.8
127
1408
1498
1307
Figure 2
active
0.8
73
1354
1424
1301
Figure 3
active
1.6
220
1534
1684
1475
Figure 4
active
2
148
1505
1481
1421
Figure 5
active
1.2
127
1545
1527
1437
Figure 6
active
0/2
87
2324
2115
1877
Figure 7
-Radar interferometric results
According to this map, the maximum subsidence rate in the study area in 2017 and 2018 will be 6.4 and 5.6 respectively. Regarding the maps drawn on this plain with radar interferometry, both indicate the subsidence of the plain. The analysis of plain radar data shows that the highest elevation in the joghatay heights, and the highest subsidence level, occurred on the joveyn Plain floor.
4-Conclusion
Although most scholars consider untreated groundwater to be an important factor in groundwater depletion and the plains of Iran, the role of tectonic factors in exacerbating this phenomenon should not be overlooked. In a study conducted by Purkhosrovani et al. On the causes of the subsidence, only Duval's discussion of radar interferometry was discussed without examining tectonic indices. In this study, in addition to radar interferometry, the tectonic status of the basin was also investigated. For this purpose, geomorphic indices such as watershed shape, drainage basin asymmetry index, inverse topographic symmetry index, mountain front sinusoidal index, hipsometry integral, valley floor height to its height, river sine index, river gradient index, gradient index They offer some of the activities of the area's baby boomers. Among the morphotectonic indices that all indicate tectonic activity in the region, the VF index in the region was less than 2, which by standards is below 6 in this index indicating rising areas. Subsidence caused by tectonic movements occurs when there are two faults, graben and upwelling, and relative movement of parts causes subsidence. The fault status of the area in the southern and northern parts of the region has placed the plain in the graben position. Statistical analysis also showed that the earthquake of 1923 occurred with a magnitude of 6.4 MS. The future activity of these faults may affect the area. The active morphotectonic conditions of the basin, also showed the results of radar interferometry, in the southern part with higher elevation, parallel to subsidence in the plain. The existence of this scouring and its appearance on the radar interferometer map indicates the tectonic activity in the southern ranges
of the study area. These results indicate a significant relationship between the subsidence and its lateral elevations, suggesting that these two movements are dual. Based on the above arguments, it can be concluded that one of the factors affecting the subsidence of the Earth in the juvenile plain is due to its soft crustal motions even in equilibrium. Due to the geomorphic hazards of the basin, it is necessary to prepare a zoning map of the area for development activities and land preparation based on which control, protection, prevention or warning measures will be taken.
Highlights
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Keywords
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