The Performances of GRACE Mascon Solutions in Studying Seismic Deformations

2020 ◽  
Author(s):  
Lan Zhang ◽  
He Tang ◽  
Le Chang ◽  
Wenke Sun
Keyword(s):  
Tohoku Earthquake ◽  
Gravity Change ◽  
Mathematical Treatment ◽  
Seismic Signals ◽  
Gaussian Filter ◽  
Seismic Deformations ◽  
Gravity Changes ◽  
Grace Data ◽  
Basin Scale ◽  
Large Earthquakes

<p>The GRACE mascon solutions, called the advanced products of GRACE data, are widely used in cryosphere science or hydrology research. It has been demonstrated that the mascon solutions have the same or better performances compared with the spherical harmonic (SH) solutions at the basin scale. However, although the mascon solutions are expected to have the ability to recover the transient gravity signals due to large earthquakes, few studies have investigated the performances of the mascon solutions in studying seismic deformations systematically. In this study, we attempt to examine the performances of the mascon solutions for transient gravity signals induced by three M9 class earthquakes: the 2011 Tohoku-Oki, 2004 Sumatra and 2010 Chile earthquakes, and compare them with the SH solutions and theoretical gravity changes modelled by dislocation theory. We analyse the co-seismic gravity changes and conclude that the mascon solutions contain almost identical information as the SH solutions and can retrieve the co-seismic gravity change signals in the resolutions equivalent to the Gaussian filter radii of 210~270 km. However, the mascon solutions have other strengthening gravity change signals, with magnitudes that are the same order as that of the SH solutions and contain pre-seismic gravity change signals in the Tohoku earthquake. These strengthening and pre-seismic signals are both considered artificially introduced noise due to the mathematical treatment before releasing rather than real geophysical signals.</p>

On the separation of co- and post-seismic signals due to large earthquakes from GRACE observations

2020 ◽  
Author(s):  
Jin Li ◽  
Jianli Chen ◽  
Song-Yun Wang ◽  
Lu Tang ◽  
Xiaogong Hu
Keyword(s):  
Time Series ◽  
Seismic Signal ◽  
Seismic Signals ◽  
Fitting Method ◽  
Short Period ◽  
Gravity Recovery ◽  
Andaman Earthquake ◽  
Large Earthquakes ◽  
Temporal Gravity

<p>Satellite gravimetry observations from GRACE (Gravity Recovery and Climate Experiment) and GRACE Follow-On are widely used to study the co-seismic and post-seismic deformations caused by large earthquakes. Temporal gravity changes from GRACE provide good constraints to investigate the fault slips of large earthquakes especially for oceanic areas. However, reliable retrieval of seismic signals is still challenging due to large uncertainties and limited spatial and temporal resolutions of GRACE observations. To extract the co- and post-seismic signals from GRACE, the time series fitting method based on least squares is commonly used. In the time series fitting, the earthquake occurrence time parameter (t0) is usually set at the mid-month point, since most available GRACE time-variable data are monthly solutions. Nevertheless, a lot of large earthquakes did not occur exactly at mid-month. By simulative tests, we demonstrate that the commonly used mid-month approximation for the fitting parameter t0 can cause noticeable bias for the seismic signal extraction. The several-days deviation in the parameter t0 leads to obvious difference for the time series fitting of seismic signals, since the post-seismic changes are rapid and significant within a short period after the earthquake. With the case study of the 2004 Mw9.1 Sumatra-Andaman earthquake (which occurred on December 26), we indicate that the bias due to the commonly used mid-month t0 approximation reaches above 10 percent amplitude of the extracted co-seismic signals. Thus the exact date for the fitting parameter t0 should be used for more reliable separation of the co- and post-seismic signals from GRACE observations.</p>

Review: Source Models of the 2011 Tohoku Earthquake and Long-Term Forecast of Large Earthquakes

2014 ◽  
Vol 9 (3) ◽  
pp. 272-280 ◽  
Author(s):  
Kenji Satake ◽  
◽  
Yushiro Fujii ◽  
Keyword(s):  
Tohoku Earthquake ◽  
2011 Tohoku Earthquake ◽  
Tsunami Source ◽  
The 2011 Tohoku Earthquake ◽  
Term Forecast ◽  
Trench Axis ◽  
Source Models ◽  
Plate Coupling ◽  
Large Earthquakes

Numerous source models of the 2011 Tohoku earthquake have been proposed based on seismic, geodetic and tsunami data. Common features include a seismic moment of ∼ 4×1022 Nm, a duration of up to ∼ 160 s, and the largest slip of about 50 m east of the epicenter. Exact locations of this largest slip differ with the model, but all show considerable slip near the trench axis where plate coupling was considered to be weak and also at deeper part where M∼7 earthquakes repeatedly occurred at average 37-year intervals. The long-term forecast of large earthquakes made by the Earthquake Research Committee was based on earthquakes occurring in the last few centuries and did not consider such a giant earthquake. Among the several issues remaining unsolved is the tsunami source model. Coastal tsunami height distribution requires a tsunami source delayed by a few minutes and extending north of the epicenter, but seismic data do not indicate such a delayed rupture and there is no clear evidence of additional sources such as submarine landslides along the trench axis. Long-term forecast of giant earthquakes must incorporate non-characteristic models such as earthquake occurrence supercycles, assessments of maximum earthquake size independent of past data, and plate coupling based on marine geodetic data. To assess ground shaking and tsunami in presumed M∼9 earthquakes, characterization and scaling relation fromglobal earthquakes must be used.

Analytical modelling and joint inversion of surface displacements and gravity changes at volcanoes

2021 ◽  
Author(s):  
Mehdi Nikkhoo ◽  
Eleonora Rivalta
Keyword(s):  
Source Parameters ◽  
Surface Displacement ◽  
Point Sources ◽  
Gravity Change ◽  
Density Estimate ◽  
Mass Change ◽  
Long Valley Caldera ◽  
Gravity Changes ◽  
Surface Displacements ◽  
Volcanic Reservoirs

<p>Gravity change observations at volcanoes provide information on the location and mass change of intruded magma bodies. Gravity change and surface displacement observations are often combined in order to infer the density of the intruded materials. Previous studies have highlighted that it is crucial to account for magma compressibility and the shape of the gravity change and deformation source to avoid large biases in the density estimate. Currently, an analytical model for the deformation field and gravity change due to a source of arbitrary shape is lacking, affecting our ability to perform rapid inversions and assess the nature of volcanic unrest.  </p><p>Here, we propose an efficient approach for rapid joint-inversions of surface displacement and gravity change observations associated with underground pressurized reservoirs. We derive analytical solutions for deformations and gravity changes due to the volume changes of triaxial point-sources in an isotropic elastic half-space. The method can be applied to  volcanic reservoirs that are deep compared to their size (far field approximation). We show that the gravity changes not only allow inferring mass changes within the reservoirs, but also help better constrain location, shape and the volume change of the source. We discuss how the inherent uncertainties in the realistic shape of volcanic reservoirs are reflected in large uncertainties on the density estimates. We apply our approach to the surface displacements and gravity changes at Long Valley caldera over the 1985-1999 time period. We show that gravity changes together with only vertical displacements are sufficient to constrain the mass change and all the other source parameters. We also show that while mass change is well constrained by gravity change observations the density estimate is more uncertain even if the magma compressibility is accounted for in the model.</p>

scholarly journals Medium-Term Earthquake Forecast Using Gravity Monitoring Data: Evidence from the Yutian and Wenchuan Earthquakes in China

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Yiqing Zhu ◽  
F. Benjamin Zhan
Keyword(s):  
Large Earthquake ◽  
Additional Research ◽  
Monitoring Data ◽  
Medium Term ◽  
Earthquake Forecast ◽  
Gravity Changes ◽  
Earthquakes In China ◽  
China Earthquake ◽  
Regional Gravity ◽  
Large Earthquakes

Gravity changes derived from regional gravity monitoring data in China from 1998 to 2005 exhibited noticeable variations before the occurrence of two large earthquakes in 2008 in China—the 2008 Yutian (Xinjiang)Ms=7.3earthquake and the 2008 Wenchuan (Sichuan)Ms=8.0earthquake. Based on these gravity variations, a group of researchers at the Second Crust Monitoring and Application Center of China Earthquake Administration made a suggestion in December of 2006 that the possibility for the Yutian (Xinjiang) and Wenchuan (Sichuan) areas to experience a large earthquake in either 2007 or 2008 was high. We review the gravity monitoring data and methods upon which the researchers reached these medium-term earthquake forecasts. Experience related to the medium-term forecasts of the Yutian and Wenchuan earthquakes suggests that gravity changes derived from regional gravity monitoring data could potentially be a useful medium-term precursor of large earthquakes, but significant additional research is needed to validate and evaluate this hypothesis.

scholarly journals Joint estimate of the co-seismic 2011 Tohoku earthquake fault slip and post-seismic viscoelastic relaxation by GRACE data inversion

2019 ◽  
Author(s):  
G Cambiotti
Keyword(s):  
Temporal Resolution ◽  
Subduction Zones ◽  
Gravity Data ◽  
Tohoku Earthquake ◽  
Fault Slip ◽  
2011 Tohoku Earthquake ◽  
The 2011 Tohoku Earthquake ◽  
Physical Constraints ◽  
Megathrust Earthquakes ◽  
Grace Data

SUMMARY Satellite-derived gravity data offer a novel perspective for understanding the physics of megathrust earthquakes at subduction zones. Nonetheless, their temporal resolution and observational errors make it difficult to discern the different phases of the seismic cycle, as the elastostatic deformation (co-seismic) and the stress relaxation by viscous flow (post-seismic). To overcome these difficulties and to take advantage of the physical constraints on the temporal evolution and on the spatial pattern of the earthquake-induced gravity disturbances, we have jointly estimated the fault slip of the 2011 Tohoku earthquake and the rheological stratification by means of a Bayesian inversion of GRACE data time series and within the framework of spherically symmetric self-gravitating compressible viscoelastic Earth models. This approach, in addition to improve the exploitation of satellite-derived gravity data, allows us (i) to constrain the fault slip taking advantage of information from both the co- and post-seismic signatures and (ii) to investigate the trade-off between the fault slip and the shallow rheological stratification. In this respect, it can be used to improve the modelling of crustal displacements from GPS data, even if their higher accuracy and temporal resolution allow to discriminate well the co-seismic signature from the others.

scholarly journals Seasonal gravity changes estimated from GRACE data

2010 ◽  
Vol 1 (1) ◽  
pp. 57-63 ◽  
Author(s):  
Zhengbo Zou ◽  
Hui Li ◽  
Zhicai Luo ◽  
Lelin Xing
Keyword(s):  
Gravity Changes ◽  
Grace Data

Analysis of exploitation‐induced gravity changes at Wairakei Geothermal Field

Geophysics ◽  
1986 ◽  
Vol 51 (8) ◽  
pp. 1647-1660 ◽  
Author(s):  
Richard G. Allis ◽  
Trevor M. Hunt
Keyword(s):  
Geothermal Field ◽  
Gravity Change ◽  
Gravity Models ◽  
Liquid Temperature ◽  
Surrounding Area ◽  
Liquid Pressure ◽  
Induced Gravity ◽  
Gravity Changes ◽  
Flow Equilibrium ◽  
The 1960S

Gravity changes (corrected for subsidence) of up to -1 000 (±300) μGal have occurred in the [Formula: see text] area of the production bore field at Wairakei, and smaller decreases extend over a [Formula: see text] surrounding area. The largest part of these decreases occurred during the 1960s; since then the net gravity change for the whole field has been zero, indicating mass flow equilibrium. The principal causes of gravity change have been deep liquid pressure drawdown which resulted in formation of a steam zone, subsequent saturation changes in the steam zone, liquid temperature decline, and groundwater level changes. Gravity models suggest saturation of the steam zone was 0.7 (±0.1) in 1962 and decreased to 0.6 by 1972. Gravity increases in the northern and eastern bore field since the early 1970s are attributed to cool water invading the steam zone.

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