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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. Journal of Geophysical Research. Solid Earth, 126 (6). Art. No. e2021JB021693. ISSN 2169-9313. doi:10.1029/2021JB021693.

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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:Article
Related URLs:
URLURL TypeDescription ItemDiscussion Paper - version 2 ItemDiscussion Paper - version 1 ItemAdvance Land Observation Satellite ItemGEBCO_2020 Grid ItemW-phase code
https://www.globalcmt.orgRelated ItemGCMT Catalog 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:© 2021 American Geophysical Union. Issue Online: 04 June 2021; Version of Record online: 04 June 2021; Accepted manuscript online: 17 May 2021; Manuscript accepted: 11 May 2021; Manuscript revised: 28 April 2021; Manuscript received: 19 January 2021. The authors thank the editor, Yehuda Ben-Zion, and the two reviewers, Göran Ekström and Babak Hejrani, for their valuable comments and suggestions. The authors also thank Kiwamu Nishida, Shunsuke Takemura, and Tatsuhiko Saito for helpful discussion. This study is funded by the JSPS KAKENHI (Grant numbers JP17J02919, JP20J01689, and JP19K04034), by the JST J-RAPID (Grant number JPMJJR1805), and partially by the Gordon and Betty Moore Foundation. Osamu Sandanbata's travel to the California Institute of Technology was supported by the Oversea Internship Program of the Earthquake Research Institute, the University of Tokyo. Data Availability Statement: The authors 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 The authors obtained earthquake information from the GCMT Catalog ( The authors plotted focal mechanisms representing moment tensors with a MATLAB code developed by James Conder (available from MATLAB Central File Exchange ( Data sets 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
Gordon and Betty Moore FoundationUNSPECIFIED
Earthquake Research InstituteUNSPECIFIED
University of TokyoUNSPECIFIED
Subject Keywords:caldera; moment tensor inversion; ring fault; Sierra Negra caldera; surface wave; volcanic earthquake
Issue or Number:6
Record Number:CaltechAUTHORS:20210126-152655426
Persistent URL:
Official Citation:Sandanbata, O., Kanamori, H., Rivera, L., Zhan, Z., Watada, S., & Satake, K. (2021). Moment tensors of ring-faulting at active volcanoes: Insights into vertical-CLVD earthquakes at the Sierra Negra Caldera, Galápagos Islands. Journal of Geophysical Research: Solid Earth, 126, e2021JB021693.
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:09 Jun 2021 21:20

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