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Moment Tensors of Ring-Faulting at Active Volcanoes: Insights into Vertical-CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands

Sandanbata, Osamu and Kanamori, Hiroo and Rivera, Luis and Zhan, Zhongwen and Watada, Shingo and Satake, Kenji (2021) Moment Tensors of Ring-Faulting at Active Volcanoes: Insights into Vertical-CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands. . (Unpublished)

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Moderate earthquakes (M_w > 5) with moment tensors (MTs) dominated by a vertical compensated-linear-vector-dipole (vertical-CLVD) component are often generated by dip slip along a curved ring-fault system at active volcanoes. However, relating their MTs to ring-fault parameters has been proved difficult. The objective of this study is to find a robust way of estimating some ring-fault parameters based on their MT solutions obtained from long-period seismic records. We first model the MTs of idealized ring-faulting and show that MT components representing the vertical-CLVD and vertical strike-slip mechanisms are resolvable by the deviatoric MT inversion using long-period seismic waves, whereas a component representing the vertical dip-slip mechanism is indeterminate owing to a shallow source depth. We then propose a new method for estimating the arc angle and orientation of ring-faulting using the two resolvable MT components. For validation, we study a vertical-CLVD earthquake that occurred during the 2005 volcanic activity at the Sierra Negra caldera, Galápagos Islands. The resolvable MT components are stably determined with long-period seismic waves, and our estimation of the ring-fault parameters is consistent with the ring-fault geometry identified by previous geodetic studies and field surveys. We also estimate ring-fault parameters of two earthquakes that took place during the 2018 activity at the caldera, revealing significant differences between the two earthquakes in terms of slip direction and location. These results show the usefulness of our method for estimating ring-fault parameters, enabling us to examine the kinematics and structures below active volcanoes with ring faults that are distributed globally.

Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription Paper - version 2 Paper - version 1 ItemAdvance Land Observation Satellite ItemGEBCO_2020 Grid ItemW-phase code
https://www.globalcmt.orgRelated ItemGCMT Catalo ItemMATLAB code of MT solutions
Sandanbata, Osamu0000-0002-2361-8482
Kanamori, Hiroo0000-0001-8219-9428
Rivera, Luis0000-0002-0726-5445
Zhan, Zhongwen0000-0002-5586-2607
Watada, Shingo0000-0001-9924-968X
Satake, Kenji0000-0002-3368-3085
Additional Information:The copyright holder for this preprint is the author/funder. Version 1: Sat, 23 Jan 2021 08:51:30; Version 2: Mon, 26 Apr 2021 08:30:42. We thank the editor, Yehuda Ben-Zion, and the two reviewers, Göran Ekström and Babak Hejrani, for their valuable comments and suggestions. We also thank Kiwamu Nishida, Shunsuke Takemura, and Tatsuhiko Saito for helpful discussion. This work is funded by the JSPS KAKENHI (grant numbers JP17J02919, JP20J01689, and JP19K04034) and by the JST J-RAPID (grant number JPMJJR1805). O.S.’s travel to California Institute of Technology was supported by the Oversea Internship Program of Earthquake Research Institute, the University of Tokyo. The original manuscript has been edited by Stallard Scientific Editing ( Data Availability Statement: We used topography and bathymetry data downloaded from the Advance Land Observation Satellite (ALOS) World 3D–30 m DEM (AW3D30; available from provided by the Japan Aerospace Exploration Agency (JAXA), and from GEBCO_2020 Grid (available from The W-phase code can be downloaded from We obtained earthquake information from the GCMT Catalog ( We plotted focal mechanisms representing moment tensors with a MATLAB code developed by James Conder (available from MATLAB Central File Exchange ( Datasets of MT solutions obtained in this study and used for Figures 7 and S1 are provided in an open access repository, Zenodo (
Group:Seismological Laboratory
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)JP17J02919
Japan Society for the Promotion of Science (JSPS)JP20J01689
Japan Society for the Promotion of Science (JSPS)JP19K04034
Japan Science and Technology AgencyJPMJJR1805
University of TokyoUNSPECIFIED
Subject Keywords:Geophysics/Seismology and Seismic Exploration, Geophysics/Solid-Earth and Geophysics, Geophysics
Record Number:CaltechAUTHORS:20210126-152655426
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107734
Deposited By: Tony Diaz
Deposited On:26 Jan 2021 23:43
Last Modified:28 Apr 2021 21:03

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