S008-04
Improving the Resolution of the Isotropic Moment Tensor Component using Rotational Ground Motions

Tuesday, 8 December 2020: 04:14
Virtual
Stefanie Donner1, Peter Gaebler2, Thomas Plenefisch1, Frank Krüger3, Mustać Marija4, Babak Hejrani5, Hrvoje Tkalcic6 and Heiner Igel7, (1)BGR Federal Institute for Geosciences and Natural Resources, Hannover, Germany, (2)Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Hannover, Germany, (3)University of Potsdam, Potsdam, Germany, (4)University of Zagreb, Department of Geophysics, Zagreb, Croatia, (5)Geoscience Australia, Symonston, ACT, Australia, (6)Australian National University, Research School of Earth Sciences, Canberra, ACT, Australia, (7)Ludwig Maximilians University of Munich, Munich, Germany
Recorded Presentation
Abstract:
Seismic moment tensors are an important tool to understand tectonic and geodynamic processes in the crust. They not only tell us about the directions crustal blocks moved during an earthquake but decomposed (i.e. separated into different source contributions) they also tell us about volume changes (isotropic - ISO - part). This ISO part is especially important for a better understanding of volcanic risk, induced and swarm seismicity, as well as explosive sources such as nuclear tests.

Rotational ground motions, along with translational ground motions, are needed to describe the entire wavefield excited by a seismic source. They represent the vectorial curl of the wavefield. In previous studies, we could show that inverting both ground motions together, the resolution of the moment tensor can be improved significantly.

In a synthetic set-up for the Korean peninsula we compared the resolvability of the Mw 5.4 strike-slip earthquake of 2016 in the Republic of Korea with the 2013 nuclear test of the Democratic People’s Republic of Korea. Applying Bayesian inversion, we tested three different frequency bands including varying amounts of surface- and body-wave energy. We also tested the inversion with Green‘s functions based on 1- and 3-dimensional structural models. The reliability of both source mechanisms benefit form both, the 3-dimensional structure and the rotational ground motions, even more in the higher frequency ranges. Thus, also the reliability of the ISO part is increased.

In the Korean study, the shallow-burried nuclear yield introduces well known difficulties to the inversion which hamper the detailed analyses of the ISO resolution. Therefore, we selected the Bohemian/Vogtland region as a second study area. Here, frequent swarm activity is connected with fluid flow within the crust. Although this connection is well known, the detailed mechanism behind this connection is still enigmatic. A comprehensive analysis of seismic moment tensors and their ISO part could contribute to the resolution of this question. In preparation of the installation of two rotational sensors, we performed several test inversions to determine their best position with respect to the resolvability of the moment tensor and its ISO part. We aim to present selected results of this study.

<< Previous Abstract | Next Abstract >>