REGARD: A new GNSS‐based real‐time finite fault modeling system for GEONET

Abstract

The short‐period seismometer‐based magnitude saturation problem, especially for events with magnitude > 8, can be improved by a real‐time Global Navigation Satellite System (GNSS) positioning technique, which has enabled rapid estimation of a finite fault model for a large earthquake without any saturation. A new real‐time fault modeling system based on the GNSS Earth Observation Network (GEONET) is developed and is under experimental operation in Japan. In this paper, we present the newly developed system REGARD (the Real‐time GEONET Analysis system for Rapid Deformation monitoring), which consists of real‐time GNSS positioning, automatic detection of coseismic displacement by the event, and quasi real‐time finite fault model inversion routines. The performance of the automatic event detection system is tested through experimental real‐time operation based on GEONET data for 2 months. Furthermore, we also test the reliability of the finite fault model inversion routines using real raw GNSS data observed for past large earthquakes: the 2003 Tokachi‐oki earthquake (moment magnitude (Mw) 8.3), the 2011 Tohoku earthquake (Mw 9.0), and the 2011 off‐Ibaraki earthquake (Mw 7.7). A simulated 1707 Hoei‐type Nankai Trough earthquake (Mw 8.7) is also tested. The real‐time experimental operation shows that real‐time GNSS positioning is precise enough to detect all the tested earthquakes, and the inversion results demonstrate that the REGARD can reliably estimate the earthquake size and its extent within 3 min after the origin time. These results suggest that the REGARD system will complement the seismometer‐based magnitude determination system.

Space geodetic tools provide early warnings for earthquakes and volcanic eruptions

“…A difference between seismic and geodetic early warning is that the GNSS observation can measure oscillations with lower frequencies and also permanent displacements. As a result, underestimating the earthquake size is less likely with the GNSS measurements [e.g., Blewitt et al , ; Ohta et al , ; Kawamoto et al , ] than using only seismograms, which, particular for short‐period seismograms, often underestimate the size of earthquakes with magnitude 8 or larger [e.g., Melgar et al , ]. In the case of the 2011 Tohoku‐oki earthquake ( M w =9.0), an immediate estimate of the magnitude using local short‐period seismograms only was M = 7.9, well below the actual size, leading to substantial underestimation of tsunami height and risk [ Ozaki , ].…”

Automated GNSS and Teleseismic Earthquake Inversion (AutoQuake Inversion) for Tsunami Early Warning: Retrospective and Real-Time Results

“…So far, many aforementioned GNSS approaches and related publications are based on post-event processed data and implementation. To our knowledge, real-time inversion of earthquakes just using GNSS is only feasible in regions where there is a dense GNSS network (Kawamoto et al 2016(Kawamoto et al , 2017, while a global GNSS-based earthquake source inversion system has never been reported except post-event demonstration in simulated environment.…”

Measuring offshore tsunami currents using ship navigation records

“…However, these methods estimate a point source that may be indirectly related to tsunamis, and are somehow difficult to accurately constrain the tsunami source dimension particularly for great earthquakes (Katsumata et al 2013;Hoshiba and Ozaki 2014). Earthquake-source estimation using Global Positioning System/Global Navigation Satellite System (GPS/GNSS) observations of land deformation will suitably constrain the source dimension with moment magnitude of nearshore (< 100 km from the coast) earthquakes (Melgar and Bock 2015;Kawamoto et al 2017). For greater earthquakes (M w > 8.5), in addition to the fault slip, seafloor failure due to strong ground motion likely causes a certain portion of tsunami (Kawamura et al 2014;Løvholt et al 2015).…”