Analysis of the Iranian Permanent GPS Network in the NE and E of Iran (time series and velocity fields)

Student: MAmaneh Jadidi Mardkheh
Supervisors: Prof Andrea Walpersdorf, Mathilde Vergnolle

ABSTRACT

Iran is situated in a region of collision between two major tectonic plates, the Eurasian and the Arabian plates, with a convergence rate of 25±2 mmyr-1. The historical earthquakes that occurred before the 20th century and recorded data clearly show that Iran has always been shaken by largely destructive earthquakes. This study is concentrated on the northern and eastern part of Iran.

In the first part of this study we present a combined solution of the permanent Iranian GPS network (65 stations) and campaign GPS networks. We established a combination solution with a global IGS network and compare this method with SOPAC solutions and a solution limited to the regional network. We explore the effect of the new atmospheric modelling (concerning atmospheric loading and mapping functions) in particular on the height component. We defined an optimal reference frame for our studies in Iran with 36 stations distributed densely over the whole world. We investigate the contribution of the permanent stations to improve the reference frame of campaign networks and their coordinate estimation. We explore the compatibility of permanent site velocities with close by campaign sites on bedrock. In this study, we recognized that the combination solution (regional networks and global IGS network) is the best strategy to obtain more precise coordinates with respect to the ITRF2000 reference frame. We detect that the mapping function VMF1 and the modelling of atmospheric loading improve significantly the height component. We give evidence for the use of permanent stations improving the campaign reference frames. We observed periodical subsidence of 20 cm/yr at the TOUS station and 6 cm/yr at the NISH station which are located in NE Iran close to Mashhad.
In the second part of this study, we examine 3 past large earthquakes that occurred in the NE of the Lut block, in NE Iran, to understand whether these disaster earthquakes changed the proximity of failure of the surrounding faults. The first destructive one occurred on the 31st of August 1968 (Mw 7.1). The next one occurred on the 27th of November 1979 (Mw 7.1). It is the largest event of a series of 48 events in 1979. These two M>7 earthquakes broke the East West left lateral Dasht-e-Bayaz fault system. Finally, the last disaster happened on the 10th of May 1997 and broke the north part of the SN right lateral Abiz fault system. The tendency of the rocks to fail in a brittle manner is thought to be a function of both shear and normal stresses, commonly formulated as the Coulomb failure criterion (King et al, 1994). In this study, based on the variation of the Coulomb stress failure hypothesis, we explore the possible stress triggering relationship between these three large earthquakes. We also investigate the relationship between each large earthquake with their aftershocks and evaluate the Coulomb stress variation on the surrounding faults. So we release the two large earthquakes in 1968 and 1979 were a major criterion to make advance the earthquake on Abiz fault in 1997. And also these 3 large earthquakes are activated a large kilometre area on Lut block. The variation of stating Coulomb stress changes is between 0.02-5 bars on the southern part of the Abiz fault on Sistan suture as increasing stress and has dropped by the same value on most part of area. The seismicity is high after the 1997 earthquake, and located not only in the areas that have their potential to break increased. We thus think that the earthquakes that occurred in the shadow stress areas result from another process than the static Coulomb stress perturbation caused by the preceding 3 large earthquakes and needs more consideration.

You may download a digital version of this MSc dissertation here.