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

scholarly journals On the relationship between strain rate and seismicity in the India-Asia collision zone: Implications for probabilistic seismic hazard

2021 ◽  
Author(s):  
V L Stevens ◽  
J-P Avouac
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Linear Relationship ◽  
Active Tectonics ◽  
Probabilistic Seismic Hazard ◽  
Maximum Magnitude ◽  
Collision Zone ◽  
Geodetic Strain Rate ◽  
Non Linear ◽  
Geodetic Strain

Summary The increasing density of geodetic measurements makes it possible to map surface strain rate in many zones of active tectonics with unprecedented spatial resolution. Here we show that the strain tensor rate calculated from GPS in the India-Asia collision zone represents well the strain released in earthquakes. This means that geodetic data in the India-Asia collision zone region can be extrapolated back in time to estimate strain buildup on active faults, or the kinematics of continental deformation. We infer that the geodetic strain rates can be assumed stationary through time on the timescale needed to build up the elastic strain released by larger earthquakes, and that they can be used to estimate the probability of triggering earthquakes. We show that the background seismicity rate correlates with the geodetic strain rate. A good fit is obtained assuming a linear relationship ($\dot{N} = \lambda \ \cdot \dot{\epsilon }$ where $\dot{N}$ is the density of the rate of Mw ≥ 4 earthquakes, $\dot{\epsilon }$ is strain rate and λ = 2.5 ± 0.1 × 10−3 m−2), as would be expected from a standard Coulomb failure model. However, the fit is significantly better for a non-linear relationship ($\dot{N} = \gamma _1 \cdot \dot{\epsilon }^{\gamma _2}$ with γ1 = 2.5 ± 0.6 m−2 and γ2 = 1.42 ± 0.15). The b-value of the Gutenberg-Richter law, which characterize the magnitude-frequency distribution, is found to be insensitive to the strain rate. In the case of a linear correlation between seismicity and strain rate, the maximum magnitude earthquake, derived from the moment conservation principle, is expected to be independent of the strain rate. By contrast, the non-linear case implies that the maximum magnitude earthquake would be larger in zones of low strain rate. We show that within areas of constant strain rate, earthquakes above Mw4 follow a Poisson distribution in time and and are uniformly distributed in space. These findings provide a framework to estimate the probability of occurrence and magnitude of earthquakes as a function of the geodetic strain rate. We describe how the seismicity models derived from this approach can be used as an input for probabilistic seismic hazard analysis. This method is easy to automatically update, and can be applied in a consistent manner to any continental zone of active tectonics with sufficient geodetic coverage.

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>

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 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.

A probabilistic seismic hazard model for Mainland China

2020 ◽  
Vol 36 (1_suppl) ◽  
pp. 181-209 ◽  
Author(s):  
Yufang Rong ◽  
Xiwei Xu ◽  
Jia Cheng ◽  
Guihua Chen ◽  
Harold Magistrale ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Active Faults ◽  
Mainland China ◽  
Hazard Model ◽  
Source Zone ◽  
Probabilistic Seismic Hazard ◽  
Earthquake Catalog ◽  
Geodetic Strain Rate ◽  
Geodetic Strain

We construct a probabilistic seismic hazard model for mainland China by integrating historical earthquakes, active faults, and geodetic strain rates. We delineate large seismic source zones based on geologic and seismotectonic characteristics. For each source zone, a tapered Gutenberg–Richter (TGR) distribution is used to model the total seismic activity rates. The TGR a- and b-values are calculated using a new earthquake catalog, while corner magnitudes are constrained using the seismic moment rate inferred from a geodetic strain rate model. For hazard calculations, the total TGR distribution is split into two parts, with smaller ( MW < 6.5) earthquakes being distributed within the zone using a smoothed seismicity method, and larger earthquakes put both onto active faults, based on fault slip rates and dimensions, and into the zone as background seismicity. We select ground motion models by performing residual analysis using ground motion recordings. Site amplifications are considered based on a site condition map developed using geology as a proxy. The resulting seismic hazard is consistent with the fifth-generation national seismic hazard model for most major cities.

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