scholarly journals Time-Independent Forecast Model For Large Crustal Earthquakes in Southwest Japan Using GNSS Data

2021 ◽  
Author(s):  
Takuya Nishimura
Keyword(s):  
Strain Rate ◽  
Seismic Moment ◽  
Forecast Model ◽  
Geodetic Data ◽  
Predictive Skill ◽  
Crustal Earthquakes ◽  
Geodetic Strain Rate ◽  
Likelihood Model ◽  
The Moment ◽  
Geodetic Strain

Abstract In this study, we developed a regional likelihood model for crustal earthquakes using geodetic strain rate data from southwest Japan. First, smoothed strain rate distributions were estimated from continuous GNSS measurements. Second, we removed the elastic strain rate attributed to interplate coupling on the subducting plate boundary, including the observed strain rate, under the assumption that it is not attributed to permanent loading on crustal faults. We then converted the geodetic strain rates to seismic moment rates and calculated the 30-year probability for M ≥ 6 earthquakes in 0.2 × 0.2° cells, using a truncated Gutenberg–Richter law and time-independent Poisson process. Likelihood models developed using different conversion equations, seismogenic thicknesses, and rigidities were validated using the epicenters and moment distribution of historical earthquakes. The average seismic moment rate of crustal earthquakes recorded during 1583–2020 was only 13–20 % of the seismic moment rate converted from the geodetic data, which suggests that the observed geodetic strain rate includes considerable inelastic strain. Therefore, we introduced an empirical coefficient to calibrate the moment rate converted from geodetic data with the moment rate of the earthquakes. Several statistical scores and the Molchan diagram showed that all models could predict real earthquakes better than the reference model, in which earthquakes occur uniformly in space. Models using principal horizontal strain rates exhibited better predictive skill than those using the maximum horizontal shear strain rate. There was no significant difference in the predictive skill between uniform and variable distributions for seismogenic thickness and rigidity. The preferred models suggested high 30-year-probability in the Niigata–Kobe Tectonic Zone and central Kyushu, exceeding 1% in more than half of the analyzed region. Model predictive skill was also verified by a prospective test using earthquakes recorded during 2010–2020. This study suggests that the proposed forecast model based on geodetic data can improve the regional likelihood model for crustal earthquakes in Japan in combination with other forecast models based on active faults and seismicity.

Preliminary forecast model of crustal earthquakes in southwest Japan based on GNSS data

2021 ◽  
Author(s):  
Takuya Nishimura
Keyword(s):  
Strain Rate ◽  
Probability Model ◽  
Active Faults ◽  
Inelastic Strain ◽  
Forecast Model ◽  
Strain Rates ◽  
Southwest Japan ◽  
Crustal Earthquakes ◽  
Gnss Data ◽  
Geodetic Strain

<p>In Japan, the Headquarters for Earthquake Research Promotion has developed a nationwide probabilistic earthquake model called “National Seismic Hazard Maps for Japan” since the destructive 1995 Kobe earthquake. This model covers both subduction and crustal earthquakes based on a history of past large earthquakes from seismological, archaeological, and geological data. The model for crustal earthquakes relies on geological and geomorphological data of active faults and never use geodetic data, whereas contemporary deformation of the Japanese Islands has been observed by a dense GNSS network. Here, we attempt to develop a preliminary forecast model of shallow crustal earthquakes using GNSS velocity data.</p><p>We follow the procedure of Shen et al.(2007) to calculate the forecast model. The GNSS velocities at continuous GNSS stations from April 2005 to December 2009 are used for the model in southwest Japan. Elastic deformation due to interplate coupling along the Nankai Trough is removed using the block model of Nishimura et al. (2018). Strain rate field is calculated at a grid point of 0.2º x 0.2º by a method of Shen et al (1994). The strain rates are converted to geodetic moment rates by a formula proposed in Savage and Simpson (1997). The thickness of a seismogenic layer, rigidity, b value of the Gutenberg-Richter law, and magnitude of the maximum earthquake are assumed to be 12 km, 30 GPa, 0.9, and 7.5, respectively. They are uniform in the modeled region. Previous studies (e.g., Shen-Tu et al., 1994) revealed that geodetic strain rates were much larger than seismological ones in southwest Japan because geodetic strain includes both elastic and inelastic strain. Elastic strain rates presumably equal to seismological ones on a long-term average. We compared seismic moment rates released by shallow historical earthquakes since AD1586 with the geodetic moment rates. Their ratio is 0.24 and 0.16 in the Chubu, Kinki, and Chugoku region and the whole southwest Japan. This difference is probably attributed to the distribution of historical documents and may also reflect the regionality of the ratio between elastic and inelastic strain. Applying 0.16 for calculating elastic rates and the stationary Poisson process of the earthquake occurrence, a probability of M≥6 earthquakes for 30 years ranges from 5.1 % to 0.2 % in each 0.2º x 0.2º grid of southwest Japan. We verify this probability model by using shallow (Depth≤ 20 km) M≥5 earthquakes occurred in 2010-2019, which is a period after the used GNSS data. The number of earthquakes was 36, which is roughly concordant to the predicted number of the model (3.04 per year). About 58 % of the earthquakes occurred with 25 % of the area with the highest strain rates, which suggests many crustal earthquakes occur in high strain-rate regions. The verification suggests the preliminary forecast model has the predictive power reasonably.</p>

scholarly journals Author Correction: A Geodetic Strain Rate Model for the East African Rift System

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
D. S. Stamps ◽  
E. Saria ◽  
C. Kreemer
Keyword(s):  
Strain Rate ◽  
East African Rift ◽  
Rift System ◽  
East African Rift System ◽  
Rate Model ◽  
East African ◽  
Geodetic Strain Rate ◽  
African Rift ◽  
Geodetic Strain

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Surface and deep deformation of the great Alpine region from GNSS and seismic anisotropy measurements

2020 ◽  
Author(s):  
Simone Salimbeni ◽  
Enrico Serpelloni ◽  
Silvia Pondrelli
Keyword(s):  
Strain Rate ◽  
Seismic Anisotropy ◽  
Spatial Scales ◽  
Alpine Region ◽  
Surface Velocity ◽  
Multi Scale ◽  
The Earth ◽  
Geodetic Strain Rate ◽  
The Alps ◽  
Geodetic Strain

<p>The comparison of crustal and mantle shear directions can provide insights into the extent of crustal-mantle coupling and the dynamics guiding surface movements and active tectonics in continental deformation zones. Here we present a first attempt of comparing surface deformation from GNSS and deep deformation from seismic anisotropy observations for the Great Alpine Area, mainly through France, Switzerland, Italy, Germany and Slovenia. The developments of the European GNSS infrastructure, integrating public and private GNSS networks, allow now to precisely determining crustal deformation over the Alps. We present a new 3D surface velocity field obtained from a recent re-analysis of 22 years of GPS data obtained from >800 continuous GNSS stations operating across the Alps and its surroundings. Unlike the crust, the orientation of the strain field within the mantle cannot be directly measured and must be inferred from either mantle earthquakes or seismic observations, such as seismic anisotropy observations. We compiled a new map of SKS directions merging data collected during several experiments and available from different databases, deriving a new continuous mantle deformation pattern over the Great Alpine Region. Geodetically determined displacements of the Earth’s surface reflect the response to different processes acting at different spatial scales. In the comparison between crustal and mantle deformation we accounted for the intrinsic multi-scale characteristics of geodetic deformation measurements, estimating the geodetic strain-rate field using a multi-scale spherical wavelet-based method, where the velocity value at a given point of the Earth’s surface is obtained as a superposition of values obtained at different spatial scales. From the geodetic strain-rate tensors we computed the two planes of shear (or no-length-changes) directions, which are compared with the directions of SKS splitting over the study region.</p>

scholarly journals Long and Short Wavelength of Geodetic Strain Rate Tapering Earthquake Potential in Western Java

2021 ◽  
Vol 731 (1) ◽  
pp. 012003
Author(s):  
L S Heliani ◽  
C Pratama ◽  
A Wibowo ◽  
D P Sahara ◽  
R Ilahi ◽  
...  
Keyword(s):  
Strain Rate ◽  
Short Wavelength ◽  
Geodetic Strain Rate ◽  
Earthquake Potential ◽  
Geodetic Strain

Geodetic strain rate and earthquake size: New clues for seismic hazard studies

2012 ◽  
Vol 206-207 ◽  
pp. 67-75 ◽  
Author(s):  
Federica Riguzzi ◽  
Mattia Crespi ◽  
Roberto Devoti ◽  
Carlo Doglioni ◽  
Grazia Pietrantonio ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Geodetic Strain Rate ◽  
Earthquake Size ◽  
Geodetic Strain

Glacial Isostatic Adjustment as a process of deformation but not seismicity in Western Alps: Coupling geodetical strain rate and numerical modeling 

2021 ◽  
Author(s):  
Juliette Grosset ◽  
Stéphane Mazzotti ◽  
Philippe Vernant
Keyword(s):  
Numerical Modeling ◽  
Seismic Hazard ◽  
Strain Rate ◽  
Western Alps ◽  
Glacial Isostatic Adjustment ◽  
Strain Rates ◽  
Fault Activity ◽  
Isostatic Adjustment ◽  
Geodetic Strain Rate ◽  
Geodetic Strain

<p>In the last decade, geodetic data has become fundamental in studies of active faults, seismicity and seismic hazard. In particular, GNSS strain rates and velocities are used to constrain fault-slip rates and seismicity parameters, on the premise that these short-term (ca. 10 yr) measurements are representative of long-term (10<sup>4</sup>–10<sup>6</sup> yr) fault activity. The Western Alps are a good example of such development in a very-low-strain region with a high-density ongoing seismic activity. There, the first-order agreement between GNSS strain rates and earthquake deformation patterns suggest that a large part of the geodetic deformation observed in the area is seismic. This correlation also suggests that geodetic strain rates can provide constraints on seismicity and seismic hazard. With a numerical modeling approach, we point out the similarities between strain rates predicted for Glacial Isostatic Adjustment (GIA) from the Last Glacial Maximum and the geodetic strain rate field, suggesting that a large part of the GNSS signal is related to GIA. However, we show that the apparent compatibility between geodetic strain rates and seismicity hides a strain rate - stress paradox. In fact, stress perturbations due to GIA are not compatible with observed seismicity, and even tend to inhibit fault activity (as observed from focal mechanisms). Thus, the Western Alps present a typical example of a tectonic system where a transient deformation process precludes, or at least strongly complexifies, the use of geodetic strain rates in seismicity and seismic hazard analyses.</p>

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