Investigation of correlation of the variations in land subsidence (detected by continuous GPS measurements) and methodological data in the surrounding areas of Lake Urmia

Lake Urmia, a salt lake in the north-west of Iran, plays a valuable role in the environment, wildlife and economy of Iran and the region, but now faces great challenges for survival. The Lake is in immediate and great danger and is rapidly going to become barren desert. As a result, the increasing demands upon groundwater resources due to expanding metropolitan and agricultural areas are a serious challenge in the surrounding regions of Lake Urmia. The continuous GPS measurements around the lake illustrate significant subsidence rate between 2005 and 2009. The objective of this study was to detect and specify the non-linear correlation of land subsidence and temperature activities in the region from 2005 to 2009. For this purpose, the cross wavelet transform (XWT) was carried out between the two types of time series, namely vertical components of GPS measurements and daily temperature time series. The significant common patterns are illustrated in the high period bands from 180–218 days band (~6–7 months) from September 2007 to February 2009. Consequently, the satellite altimetry data confirmed that the maximum rate of linear trend of water variation in the lake from 2005 to 2009, is associated with time interval from September 2007 to February 2009. This event was detected by XWT as a critical interval to be holding the strong correlation between the land subsidence phenomena and surface temperature. Eventually the analysis can be used for modeling and prediction purposes and probably stave off the damage from subsidence phenomena

Coseismic Offsets due to Intermediate Depth 16 April 2013 Southeast Iran Earthquake (M-w 7.8)

The 16 April 2013 southeast Iran earthquake (M-w 7.8) is the second major earthquake in the region, including the Makran subduction zone, since 1945. This intraslab earthquake, within the subducting Arabian plate, occurred as a result of normal faulting at an intermediate depth. We report coseismic offsets from the two nearby continuously operating Global Positioning System sites that are located within 300 km of the epicenter. The coseismic offsets are consistent with the slip on the northward steeply dipping fault plane. This earthquake probably occurred in response to the slab- detachment process, and its occurrence has implications for the plate interface coupling of the Makran subduction zone

Finite fault slip models for the 11 August 2012 Varzaghan-Ahar, NW Iran earthquakes (Mw 6.4 and 6.3) from near-field GPS measurements of coseismic offsets

We use coseismic offsets, derived from continuous GPS measurements at six nearby sites, due to the twin Varzaghan-Ahar earthquakes (northwest Iran) of 11 August 2012 (Mw 6.4 and 6.3) to constrain slip distribution on the ruptures of two earthquakes. We assume that slip during the two earthquakes occurred on conjugate faults. Majority of the slip occurred during the first earthquake which involved dextral slip on the east west trending vertical plane. The earthquake involved slip at shallow depth which reached up to ∼0.9 m at the surface, consistent with the evidence of surface rupture and the observed offsets. During the second earthquake oblique slip occurred on a north–south rupture having steep dip towards east and extending towards north from the eastern edge of the first earthquake. Maximum slip of ∼0.4 m occurred at depth of ∼6–8 km. Derived moment magnitude of the first earthquake (6.45) from our analysis is consistent with the reported moment magnitude, while that of the second earthquake (6.1) is slightly underestimated from our analysis

Co-Seismic Surface Displacement Induced by the Bam Earthquake, Iran (26/12/2003, M=6.6): Insights from InSAR, GPS, SPOT5 Analyses and Levelling

Co-seismic surface deformation measurements in the vicinity of a ruptured fault provide constraints on detailed fault geometry and slip distribution at depth. Together with seismological data, they give unique insights on the mechanical behaviour of a seismic fault. Three different satellite and ground geodetic measurements of Bam earthquake (Mw 6.6, December 26, 2003) induced surface deformation are presented. Envisat ASAR interferometry provides precise and dense information. However, due to this strike-slip fault orientation, sub-pixel correlation technique applied to Spot-5 images makes more explicit the horizontal component of surface deformation. We complete these oblique and horizontal estimations of deformation with a levelling profile along the main road crossing the rupture from west to east. This geodetic data allows us to propose a dislocation model at depth. The slip vector, on a quasi-vertical fault, slightly dipping towards east, has a strike-slip component as high as 2m, while the dip-slip component appears to be small. We suggest that rupture may have been initiated at depth on the Bam fault and propagated towards surface along this new fault branch. In addition to co-seismic deformation, InSAR analysis and levelling data reveal the presence of a high-rate subsiding zone southeast of Bam city. The phenomenon is likely due to heavy water withdrawal for cultivation purpose or water supply to the Bam and Baravat inhabitants.Ultimately, we present a work in progress involving GPS and InSAR which aims to map post-seismic deformation in the vicinity of Bam. However, technical problems in GPS campaigns and atmospheric artifacts in InSAR acquisitions did not enable us to show any evidence of such a deformation so far

Distribution of the right-lateral strike-slip motion from the Main Recent Fault to the Kazerun Fault System (Zagros, Iran): Evidence from present-day GPS velocities

International audienceGPS measurements across the Kazerun Fault System in the Zagros mountain belt provide first instantaneous velocities on the different segments. These results are closely consistent with the geological fault slip rates (over 150 ka), implying stable velocities over a longer period. The present-day strike-slip motion is distributed from the Main Recent Fault to the N-trending Kazerun Fault System along a preferential en-echelon fault zone included in a more distributed fan-shape fault pattern. The Hormuz salt decoupling layer cannot be the only cause of a sedimentary spreading because seismicity attests these faults are rooted in the basement. The Dena fault (3.7 mm/yr) transfers the MRF fault slip mainly to the Kazerun (3.6 mm/yr) and slightly to the High Zagros and Sabz Pushan faults (1.5 mm/yr), and the Kazerun fault further to the Kareh Bas fault (3.4 mm/yr). Total geological horizontal offsets associated with GPS slip rates help inferring precise fault slip onset ages. The successive onsets deduced by this approach imply that the right-lateral strike-slip activity of the MRF has propagated in time southeastward to the Dena segment, and then to the Kazerun segment and to the Kareh Bas fault

Monitoring of the large slow Kahrod landslide in Alborz mountain range (Iran) by GPS and SAR interferometry

International audienceIn this study, we quantify and analyze the spatial and temporal evolution of the surface displacement of Kahrod landslide located in the center of Alborz range (Iran) within the Haraz valley. This landslide represents a threat for this main drainage axis and its numerous infrastructures. We present three sets of displacement vectors based on GPS technique. An 8-benchmark network has been surveyed four times on a 1-year period basis. It provides accurate information on the rate of displacement within the landslide, and addresses the problem of the mechanical resistance of a small hillock, down slope, under the stress imposed by the landslide. Then. this network is densified (57 marks) and measured twice in 6 months using a rapidstatic approach. This yields to a dense description of surface deformation over the whole landslide. Finally, a 1-year time series of permanent GPS recordings is presented and compared to rainfall. Furthermore, we analyze Envisat radar differential interferograms (DInSAR) spanning the same period as permanent GPS. These geodetic data allow to precisely determine the limits of the current sliding zone and to describe the spatial and temporal evolution of surface displacement. The combination of geodesy and field observations leads to a precise description of the past and present kinematics behavior of Kahrod landslide. The chaotic nature of the sliding mass suggests a first catastrophic landslide in a first episode. During the period of observation, the landslide appears to deform quite steadily, and the evidence of short-term correlation between rainfall and deformation amplitude needs to be confirmed by future measurements. Carrying on the acquisition of GPS and InSAR data within the sliding mass but also within adjacent bedrock should give fundamental information with regards to major activation processes (river sapping, water seeping, earthquakes, or failure within the frontal hill of bedrock) and their potential consequences

Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman

International audienceA network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine-Himalayan mountain belt. We present and interpret the results of two surveys performed in 1999 September and 2001 October. GPS sites in Oman show northward motion of the Arabian Plate relative to Eurasia slower than the NUVEL-1A estimates (e.g. 22 +/- 2 mm yr-1 at N8°+/- 5°E instead of 30.5 mm yr-1 at N6°E at Bahrain longitude). We define a GPS Arabia-Eurasia Euler vector of 27.9°+/- 0.5°N, 19.5°+/- 1.4°E, 0.41°+/- 0.1° Myr-1. The Arabia-Eurasia convergence is accommodated differently in eastern and western Iran. East of 58°E, most of the shortening is accommodated by the Makran subduction zone (19.5 +/- 2 mm yr-1) and less by the Kopet-Dag (6.5 +/- 2 mm yr-1). West of 58°E, the deformation is distributed in separate fold and thrust belts. At the longitude of Tehran, the Zagros and the Alborz mountain ranges accommodate 6.5 +/- 2 mm yr-1 and 8 +/- 2 mm yr-1 respectively. The right-lateral displacement along the Main Recent Fault in the northern Zagros is about 3 +/- 2 mm yr-1, smaller than what was generally expected. By contrast, large right-lateral displacement takes place in northwestern Iran (up to 8 +/- mm yr-1). The Central Iranian Block is characterized by coherent plate motion (internal deformation -1). Sites east of 61°E show very low displacements relative to Eurasia. The kinematic contrast between eastern and western Iran is accommodated by strike-slip motions along the Lut Block. To the south, the transition zone between Zagros and Makran is under transpression with right-lateral displacements of 11 +/- 2 mm yr-1

Present-day strain distribution across the Minab-Zendan-Palami fault system from dense GPS transects

International audienceP>The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr-1 of relative motion in N10 degrees E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr-1 in N10 degrees direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27 degrees N reveal a much narrower shear zone (similar to 10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a 'stacking' and a 'persistant-scatterers' approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic 'block model' inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle