Surface deformation and source modeling of Ayaz-Akhtarma mud volcano, Azerbaijan, as detected by ALOS/ALOS-2 InSAR

Kento Iio,Masato Furuya

doi:10.1186/s40645-018-0220-7

Abstract

Azerbaijan, located on the western edge of the Caspian Sea in Central Asia, has one of the highest populations of mud volcanoes in the world. We used satellite-based synthetic aperture radar (SAR) images derived from two L-band SAR satellites, ALOS/PALSAR along an ascending track from 2006 to 2011, and its successor ALOS-2/PALSAR-2 along both ascending and descending tracks from 2014 to 2017. First, we applied interferometric SAR (InSAR) technique to detect surface displacements at the Ayaz-Akhtarma mud volcano in Azerbaijan. The 35 derived interferograms indicate that the deformation of the mud volcano is largely characterized by horizontal displacement. Besides the InSAR technique, we also used multiple-aperture interferometry (MAI) to derive the surface displacements parallel to the satellite flight direction to complement the InSAR data. Using the InSAR and MAI data, we obtained 3D displacements, which indicate that the horizontal displacement is dominant relative to subsidence and possible uplift. To explain the displacements, we performed source modeling, based on the assumption of elastic dislocation theory in a half space. The derived model consists of a convex surface on which normal-fault-type slips are semi-radially distributed, causing the significant horizontal displacements with minor subsidence. The convex source surface suggests that a steady overpressure system would be maintained by constantly intruding mud and gas.

Highlights

Mud volcanism is analogous to magmatic volcanism; the materials extruded to the surface are mud, gases, and saline water originating from deeper sediments
We apply a multiple-aperture interferometry (MAI) technique to derive the surface displacements that are parallel to the satellite flight direction in order to complement the interferometric synthetic aperture radar (SAR) (InSAR) data (Bechor and Zebker, 2006), since InSAR phase is insensitive to these along-track displacements
Descending interferograms indicate that the spatial pattern of LOS changes is consistent with the previous study (Antonielli et al 2014), which, as for the ascending track, show eastern and western sectors separated at the center of the mud volcano by a near N-S boundary (Figs. 3 and 4)

Summary

Introduction

Mud volcanism is analogous to magmatic volcanism; the materials extruded to the surface are mud, gases (mostly methane), and saline water originating from deeper sediments. We apply InSAR technique to detect the surface displacements at the Ayaz-Akhtarma mud volcano, but use L-band (wavelength 23.6 cm) images from Advanced Land Observing Satellite (ALOS)/. We apply a multiple-aperture interferometry (MAI) technique to derive the surface displacements that are parallel to the satellite flight direction in order to complement the InSAR data (Bechor and Zebker, 2006), since InSAR phase is insensitive to these along-track (near north-south) displacements. We can infer the full 3D displacements at the Ayaz-Akhtarma mud volcano Based on these displacements’ data and analytical solutions of elastic dislocation theory in an elastic half-space, we derive a source model that consists of a convex fault surface with normal faulting and strike-slip, which we will use to investigate the on-going processes and their relation to the stress regime. In the MAI processing, the multi-look size was set 2 and 4 in range and azimuth directions, respectively, and we applied Goldstein-Werner’s adaptive spectral filter with the exponent of 0.7 to smooth the signals (Goldstein and Werner 1998)

Results

Discussion

Conclusions