Analysis of the coseismic slip behavior for the MW = 9.1 2011 Tohoku-Oki earthquake from satellite GOCE vertical gravity gradient

Over the past decade, the three largest and most destructive earthquakes in recent history with associated tsunamis occurred: the Mw = 9.2 Sumatra-Andamam in 2004, then the Mw = 8.8 Maule in 2010, and finally the Mw = 9.1 Tohoku- Oki in 2011. Due to the technological and scientific developments achieved in recent decades, it has been possible to study and model these phenomena with unprecedented resolution and precision. In addition to the coseismic slip models, for which joint inversions of data from various sources are carried out (e.g., teleseismic data, GNSS, INSAR, and Tsunami, among others), depicting the space-time evolution of the rupture, we have high-resolution models of the degree of interseismic coupling (based on GNSS) and also maps of seismic b-value changes. Among these advances, new Earth gravity field models allow mapping densities distribution homogeneously and with a resolution (in wavelengths) of approximately the large rupture areas of great megathrust earthquakes. In this regard, the maximum resolution of GOCE-derived static models is in the order of λ/2≈66 km, while GRACE monthly solutions are in the order of λ/2≈300 km. From the study of the static and dynamic gravitational field, it has been possible to infer mass displacements associated with these events, which have been modeled and compared to the deformation inferred using other methods, yielding very good results. In this work we study the kinematic behavior of the rupture process for one of these largest events, the Mw = 9.1 Tohoku-Oki 2011 earthquake, employing the vertical gradient of gravity derived from the GOCE satellite, finding that the maximum slip occurred close to a lobe of minimum Tzz, as was observed for other case-studies in other subduction-related settings studied in previous works (e.g., the Maule earthquake and the Sumatra-Andaman earthquake, among others). In addition, from the rupture propagation using kinematic models, it can be observed that the rupture is arrested when it approaches high-density structures and, it is enhanced when connecting with lobes of low vertical gravity gradient. We also mapped a block expressed as a low Tzz lobe, developed along the marine forearc, which is controlled by a parallel-to-the-trench normal fault that accommodates subsidence during the interseismic period, as it is coupled with the subducted slab. Then, after rupturing the plate interface, this block is decoupled promoting tectonic inversion and uplift. In this way, the hypothesis that the density structure along the forearc is the ultimate first-order factor that governs the rupture process is reinforced.Fil: Alvarez Pontoriero, Orlando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; ArgentinaFil: Gimenez, Mario Ernesto. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto Geofísico Sismológico Volponi; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; ArgentinaFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

Gradients from GOCE reveal gravity changes before Pisagua Mw = 8.2 and Iquique Mw = 7.7 large megathrust earthquakes

Considerable improvements in the measurement of the Earth gravity field from GOCE satellite mission have provided global gravity field models with homogeneous coverage, high precision and good spatial resolution. In particular, the vertical gravity gradient (Tzz), in comparison to the classic Bouguer anomaly, defines more accurately superficial mass heterogeneities. Moreover, the correction of these satellitederived data from the effect of Earth topographic masses by means of new techniques taking into account the Earth curvature, improves results in regional analyses. In a recent work we found a correlation between Tzz and slip distribution for the 2010 Maule Mw= 8.8 earthquake. In the present work, we derive the vertical gravity gradient from the last GOCE only model, corrected by the topographic effect and also by the sediments on depocenters of the offshore region at the PerueChile margin, in order to study a spatial relationship between different lobes of the gravity derived signal and the seismic sources of large megathrust earthquakes. In particular, we analyze this relation for the slip models of the 1996 Mw = 7.7 Nazca, 2001 Mw = 8.4 Arequipa, 2007 Mw = 8.0 Pisco events and for the slip models of the 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes from Schurr et al. (2014), including the previously analyzed 2010 Mw = 8.8 Maule event. Then we find a good correlation between vertical gravity gradients and main rupture zones, correlation that becomes even stronger as the event magnitude increases. Besides this, a gravity fall in the gravity gradient was noticed over the area of the main slip patches at least for the two years before 2014 Mw = 8.2 Pisagua and Mw = 7.7 Iquique earthquakes. Additionally, we found temporal variations of the gravity field after 2010 Mw = 8.8 Maule event, related to the main patches of the slip distribution, and coseismic deformation. Therefore, we analyzed vertical gravity gradient field variations as an indirect measure of the variable seismic coupling finding a potential relationship between Tzz and the seismic b-value. These relationships exemplify the strong potential of the satellite only derived models as a predictive tool to determine potential seismic energy released in a subduction segment, determining the potential size of a potential rupture zone, and in particular internal slip distribution that allows inferring coseismic displacement field at surface

Goce derived geoid changes before the Pisagua 2014 earthquake

The analysis of space – time surface deformation during earthquakes reveals the variable state of stress that occurs at deep crustal levels, and this information can be used to better understand the seismic cycle. Understanding the possible mechanisms that produce earthquake precursors is a key issue for earthquake prediction. In the last years, modern geodesy can map the degree of seismic coupling during the interseismic period, as well as the coseismic and postseismic slip for great earthquakes along subduction zones. Earthquakes usually occur due to mass transfer and consequent gravity variations, where these changes have been monitored for intraplate earthquakes by means of terrestrial gravity measurements. When stresses and correspondent rupture areas are large, affecting hundreds of thousands of square kilometres (as occurs in some segments along plate interface zones), satellite gravimetry data become relevant. This is due to the higher spatial resolution of this type of data when compared to terrestrial data, and also due to their homogeneous precision and availability across the whole Earth. Satellite gravity missions as GOCE can map the Earth gravity field with unprecedented precision and resolution. We mapped geoid changes from two GOCE satellite models obtained by the direct approach, which combines data from other gravity missions as GRACE and LAGEOS regarding their best characteristics. The results show that the geoid height diminished from a year to five months before the main seismic event in the region where maximum slip occurred after the Pisagua Mw = 8.2 great megathrust earthquake. This diminution is interpreted as accelerated inland-directed interseismic mass transfer before the earthquake, coinciding with the intermediate degree of seismic coupling reported in the region. We highlight the advantage of satellite data for modelling surficial deformation related to pre-seismic displacements. This deformation, combined to geodetical and seismological data, could be useful for delimiting and monitoring areas of higher seismic hazard potential.Facultad de Ciencias Astronómicas y Geofísica

Coseismic Deformation Detection and Quantification for Great Earthquakes Using Spaceborne Gravimetry

This Ohio State University Geodetic Science Report was prepared for, in part, and submitted to the Graduate School of the Ohio State University as a Dissertation in partial fulfillment of the requirements of the Doctor of Philosophy (PhD) degree.This research is conducted under the supervision of Professor C.K. Shum, Division of Geodetic Science, School of Earth Sciences, The Ohio State University. The research results documented in this report resulted in a PhD Dissertation by Lei Wang (2012), Division of Geodetic Science, School of Earth Sciences, The Ohio State University. This research is partially funded by grants from NASA’s Interdisciplinary Science Program (NNG04GN19G), NASA’s Ocean Surface Topography Mission (OSTM) and Physical Oceanography Program (JPL1283230), the Air Force Materiel Command (FA8718-07-C-0021), and NSF’s Division of Earth Sciences (EAR-1013333). We would like to acknowledge Professor Frederik J. Simons, Department of Geosciences, Princeton University, for his hosting of Dr. Lei Wang for the summer visits.Because of Earth’s elasticity and its viscoelasticity, earthquakes induce mass redistributions in the crust and upper mantle, and consequently change Earth’s external gravitational field. Data from Gravity Recovery And Climate Experiment (GRACE) spaceborne gravimetry mission is able to detect the permanent gravitational and its gradient changes caused by great earthquakes, and provides an independent and thus valuable data type for earthquake studies. This study uses a spatiospectral localization analysis employing the Slepian basis functions and shows that the method is novel and efficient to represent and analyze regional signals, and particularly suitable for extracting coseismic deformation signals from GRACE. For the first time, this study uses the Monte Carlo optimization method (Simulated Annealing) for geophysical inversion to quantify earthquake faulting parameters using GRACE detected gravitational changes. GRACE monthly gravity field solutions have been analyzed for recent great earthquakes. For the 2004 Mw 9.2 Sumatra-Andaman and 2005 Nias earthquakes (Mw 8.6), it is shown for the first time that refined deformation signals are detectable by processing the GRACE data in terms of the full gravitational gradient tensor. The GRACE-inferred gravitational gradients agree well with coseismic model predictions. Due to the characteristics of gradient measurements, which have enhanced high-frequency contents, the GRACE observations provide a more clear delineation of the fault lines, locate significant slips, and better define the extent of the coseismic deformation; For the 2010 Mw 8.8 Maule (Chile) earthquake and the 2011 Mw 9.0 Tohoku-Oki earthquake, by inverting the GRACE detected gravity change signals, it is demonstrated that, complimentary to classic teleseismic records and geodetic measurements, the coseismic gravitational change observed by spaceborne gravimetry can be used to quantify large scale deformations induced by great earthquakes

Coseismic Deformation Detection and Quantification for Great Earthquakes Using Spaceborne Gravimetry

This Ohio State University Geodetic Science Report was prepared for, in part, and submitted to the Graduate School of the Ohio State University as a Dissertation in partial fulfillment of the requirements of the Doctor of Philosophy (PhD) degree.This research is conducted under the supervision of Professor C.K. Shum, Division of Geodetic Science, School of Earth Sciences, The Ohio State University. The research results documented in this report resulted in a PhD Dissertation by Lei Wang (2012), Division of Geodetic Science, School of Earth Sciences, The Ohio State University. This research is partially funded by grants from NASA’s Interdisciplinary Science Program (NNG04GN19G), NASA’s Ocean Surface Topography Mission (OSTM) and Physical Oceanography Program (JPL1283230), the Air Force Materiel Command (FA8718-07-C-0021), and NSF’s Division of Earth Sciences (EAR-1013333). We would like to acknowledge Professor Frederik J. Simons, Department of Geosciences, Princeton University, for his hosting of Dr. Lei Wang for the summer visits.Because of Earth’s elasticity and its viscoelasticity, earthquakes induce mass redistributions in the crust and upper mantle, and consequently change Earth’s external gravitational field. Data from Gravity Recovery And Climate Experiment (GRACE) spaceborne gravimetry mission is able to detect the permanent gravitational and its gradient changes caused by great earthquakes, and provides an independent and thus valuable data type for earthquake studies. This study uses a spatiospectral localization analysis employing the Slepian basis functions and shows that the method is novel and efficient to represent and analyze regional signals, and particularly suitable for extracting coseismic deformation signals from GRACE. For the first time, this study uses the Monte Carlo optimization method (Simulated Annealing) for geophysical inversion to quantify earthquake faulting parameters using GRACE detected gravitational changes. GRACE monthly gravity field solutions have been analyzed for recent great earthquakes. For the 2004 Mw 9.2 Sumatra-Andaman and 2005 Nias earthquakes (Mw 8.6), it is shown for the first time that refined deformation signals are detectable by processing the GRACE data in terms of the full gravitational gradient tensor. The GRACE-inferred gravitational gradients agree well with coseismic model predictions. Due to the characteristics of gradient measurements, which have enhanced high-frequency contents, the GRACE observations provide a more clear delineation of the fault lines, locate significant slips, and better define the extent of the coseismic deformation; For the 2010 Mw 8.8 Maule (Chile) earthquake and the 2011 Mw 9.0 Tohoku-Oki earthquake, by inverting the GRACE detected gravity change signals, it is demonstrated that, complimentary to classic teleseismic records and geodetic measurements, the coseismic gravitational change observed by spaceborne gravimetry can be used to quantify large scale deformations induced by great earthquakes

Source Parameters Inversion for Recent Large Undersea Earthquakes from GRACE Data

This Report was prepared for and submitted to the Graduate School of the Ohio State University as a dissertation in partial fulfillment of the requirements for the PhD degree.This research is conducted under the supervision of Professor C.K. Shum, Division of Geodetic Science, School of Earth Sciences, The Ohio State University. This research is primarily supported by NASA’s Earth and Space Science Fellowship (ESSF) Program (Grant NNX12AO06H), partially supported by National Science Foundation (NSF) Division of Earth Sciences (Grant EAR-1013333). GRACE data products are from NASA’s PODAAC via Jet Propulsion Laboratory/California Institute of Technology (JPL), University of Texas Center for Space Research (CSR), and GeoForschungsZentrum Potsdam (GFZ). Preliminary GPS time series provided by the ARIA team at JPL and Caltech. All original GEONET RINEX data were provided to California Institute of Technology by the Geospatial Information Authority (GSI) of Japan. Some figures in this paper were generated using the Generic Mapping Tools (GMT) [Wessel and Smith, 1991]. This work was also supported in part by an allocation of computing resources from the Ohio Supercomputer Center (http://www.osc.edu).The north component of gravity and gravity gradient changes from the Gravity Recovery And Climate Experiment (GRACE) are used to study the coseismic gravity change for five earthquakes over the last decade: the 2004 Sumatra-Andaman earthquake, the 2007 Bengkulu earthquake, the 2010 Maule, Chile earthquake, the 2011 Tohoku earthquake, and the 2012 Indian Ocean earthquakes. We demonstrate the advantage of these north components to reduce north-south stripes and preserve higher spatial resolution signal in GRACE Level 2 (L2) monthly Stokes Coefficients data products. By using the high spherical harmonic degree (up to degree 96) data products and the innovative GRACE data processing approach developed in this study, the retrieved gravity change is up to – 34±1.4 μGal for the 2004 Sumatra and 2005 Nias earthquakes, which is by far the highest coseismic signal retrieved among published studies. Our study reveals the detectability of earthquakes as small as Mw 8.5 (i.e., the 2007 Bengkulu earthquake) from GRACE data. The localized spectral analysis is applied as an efficient method to determine the practical spherical harmonic truncation degree leading to acceptable signal-to-noise ratio, and to evaluate the noise level for each component of gravity and gravity gradient change of the seismic deformations. By establishing the linear algorithm of gravity and gravity gradient change with respect to the double-couple moment tensor, the point source parameters are estimated through the least squares adjustment combined with the simulated annealing algorithm. The GRACE-inverted source parameters generally agree well with the slip models estimated using other data sets, including seismic, GPS, or combined data. For the 2004 Sumatra- Andaman and 2005 Nias earthquakes, GRACE data produce a shallower centroid depth (9.1 km) compared to the depth (28.3 km) from GPS data, which may be explained by the closer-to-trench centroid location and by the aseismic slip over the shallow region. For the 2011 Tohoku earthquake, the inversions from two different GRACE data products and two different forward modeling produce similar source characteristics, with the centroid location southwest of and the slip azimuth 10° larger than the GPS/seismic solutions. The GRACE-estimated dip angles are larger than that from GPS/seismic data for the 2004 Sumatra-Andaman and 2005 Nias earthquakes, the 2010 Maule, Chile earthquake, and the 2007 Bengkulu earthquake. These differences potentially show the additional offshore constraint from GRACE data, compared to GPS/seismic data. With more accurate and higher spatial resolution measurements anticipated from the GRACE Follow-on mission, with a scheduled launch date in 2017, we anticipate the data will be sensitive to even smaller earthquake signals. Therefore, GRACE type observations will hopefully become a more viable measurement to further constrain earthquake focal mechanisms

Remote Sensing by Satellite Gravimetry

Over the last two decades, satellite gravimetry has become a new remote sensing technique that provides a detailed global picture of the physical structure of the Earth. With the CHAMP, GRACE, GOCE and GRACE Follow-On missions, mass distribution and mass transport in the Earth system can be systematically observed and monitored from space. A wide range of Earth science disciplines benefit from these data, enabling improvements in applied models, providing new insights into Earth system processes (e.g., monitoring the global water cycle, ice sheet and glacier melting or sea-level rise) or establishing new operational services. Long time series of mass transport data are needed to disentangle anthropogenic and natural sources of climate change impacts on the Earth system. In order to secure sustained observations on a long-term basis, space agencies and the Earth science community are currently planning future satellite gravimetry mission concepts to enable higher accuracy and better spatial and temporal resolution. This Special Issue provides examples of recent improvements in gravity observation techniques and data processing and analysis, applications in the fields of hydrology, glaciology and solid Earth based on satellite gravimetry data, as well as concepts of future satellite constellations for monitoring mass transport in the Earth system

the coseismic slip distribution of a shallow subduction fault constrained by prior information the example of 2011 tohoku mw 9 0 megathrust earthquake

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Modelling co- and post-seismic displacements revealed by InSAR, and their implications for fault behaviour

The ultimate goal of seismology is to estimate the timing, magnitude and potential spatial extent of future seismic events along pre-existing faults. Based on the rate-state friction law, several theoretical physical earthquake models have been proposed towards this goal. Tectonic loading rate and frictional properties of faults are required in these models. Modern geodetic observations, e.g. GPS and InSAR, have provided unprecedented near-field observations following large earthquakes. In theory, according to the frictional rate and state asperity earthquake model, velocity-weakening regions holding seismic motions on faults should be separated with velocity-strengthening regions within which faults slip only aseismically. However, early afterslip following the 2011 MW 9.1 Tohoku-Oki earthquake revealed from GPS measurements was largely overlaid on the historical rupture zones, which challenged the velocity weakening asperity model. Therefore, the performance of the laboratory based friction law in the natural events needs further investigation, and the factors that may affect the estimates of slip models through geodetic modelling should also be discussed systematically. In this thesis, several moderate-strong events were investigated in order to address this important issue. The best-fit co- and post-seismic slip models following the 2009 MW 6.3 Haixi, Qinghai thrust-slip earthquake determined by InSAR deformation time-series suggest that the maximum afterslip is concentrated in the same area as the coseismic slip model, which is similar to the patterns observed in the 2011 Japan earthquake. In this case, complex geometric asperity may play a vital role in the coseismic nucleation and postseismic faulting. The major early afterslip after the 2011 MW 7.1 Van mainshock, which was revealed by one COSMO-SkyMed postseismic interferogram, is found just above the coseismic slip pattern. In this event, a postseismic modelling that did not allow slip across the coseismic asperity was also tested, suggesting that the slip model without slip in the asperities can explain the postseismic observations as well as the afterslip model without constraints on slip in the asperities. In the 2011 MW 9.1 Tohoku-Oki earthquake, a joint inversion with the GRACE coseismic gravity changes and inland coseismic GPS observations was conducted to re-investigate the coseismic slip model of the mainshock. A comparison of slip models from these different datasets suggests that significant variations of slip models can be observed, particularly the locations of the maximum slips. The joint slip model shows that the maximum slip of ~42 m appears near the seafloor surface close to the Japan Trench. Meanwhile, the accumulative afterslip patterns (slip >2 m) determined in previous studies appear in spatial correlation with the Coulomb stress changes generated using the joint slip model. As a strike-slip faulting event, the 2011 MW 6.8 Yushu earthquake was also investigated through co- and post-seismic modelling with more SAR data than was used in previous study. Best slip models suggest that the major afterslip is concentrated in shallow parts of the faults and between the two major coseismic slip patterns, suggesting that the performance of the rate and state frictional asperity model is appropriate in this event. Other postseismic physical mechanisms, pore-elastic rebound and viscoelastic relaxation have also been examined, which cannot significantly affect the estimate of the shallow afterslip model in this study. It is believed that the shallow afterslip predominantly controlled the postseismic behaviour after the mainshock in this case. In comparison to another 21 earthquakes investigated using geodetic data from other studies, complementary spatial extents between co- and post-seismic slip models can be identified. The 2009 MW 6.3 Qinghai earthquake is an exceptional case, in which the faulting behaviours might be dominated by the fault structure (e.g. fault bending). In conclusion, the major contributions from this thesis include: 1) the friction law gives a first order fit in most of natural events examined in this thesis; 2) geometric asperities may play an important role in faulting during earthquake cycles; 3) significant uncertainties in co- and post-seismic slip models can appreciably bias the estimation of fault frictional properties; 4) new insights derived from each earthquake regarding their fault structures and complex faulting behaviours have been observed in this thesis; and (5) a novel package for geodetic earthquake modelling has been developed, which can handle multiple datasets including InSAR, GPS and land/space based gravity changes

Analysis of earthquake signals by spaceborne gravimetry

The Gravity Recovery And Climate Experiment (GRACE) mission was launched on Mar. 17, 2002 and has provided the scientists with the gravity data for nearly ten years. The time variable gravity field provided by the GRACE has improved our knowledge of the earth in many fields such as hydrology, oceanography and glaciology. But compared to those “hot” fields, the publications of GRACE in seismology is considerably less. However, GRACE can provide scientists with an independent observation of the earthquake process. Coincidentally, some of the largest earthquakes are within GRACE’s life span - Sumatra-Andaman Earthquake (Indonesia) 2004, Maule Earthquake (Chile) 2010 and Tohoku Earthquake (Japan) 2011. Furthermore, a smaller earthquake - Sichuan Earthquake (China) 2008 has also been examined to test whether the GRACE can detect earthquakes smaller than Mw = 8.0. Different from the traditional methods of the earthquake researches, the gravity method has its advantages: 1. Massive: global scale; 2. Insight: gravity changes can reveal the underground mass changes which do not cause so much motion on the earth surface; 3. Convenient: superior to the traditional methods, the spaceborne gravimetry can get the data from the ocean and glacier parts. The conditions of the data are different among these four earthquakes. The procedures to eliminate the GRACE observation errors and unwanted geophysical data are necessary. First, the C20 term should be replaced by the Satellite Laser Ranging (SLR) data. Second, the hydrology signal especially in the regions of Chile and Sichuan should be eliminated by the Global Land Data Assimilation System (GLDAS) model. Third, Fan filter or Gauss filter 350 km should be applied. Time series analysis by the two-phase changepoint detection and hypothesis testing are applied for each earthquake which is a point-wise analysis. Least squares adjustment is performed on each point to display the coseismic and postseismic signals. Meanwhile, the surface analysis is done by the Empirical Orthogonal Functions (EOF) as it has a flexible base which can suit the data automatically. Although the observation errors have been removed as much as possible, the limited spatial and time resolutions of the GRACE satellite and to retrieve relatively weak earthquake signal among the strong hydrological signals are still problems in the analysis. GRACE can detect some of the large earthquakes, but it depends on the earthquake type, area and the length of the time-series before and after the earthquake. Both coseismic signal and postseismic signal are detected in Sumatra-Andaman Earthquake. Meanwhile, there is no significant coseismic signal in the time series of Sichuan Earthquake, but the EOF detects suspicious earthquake signal in mode 2 with the magnitude less than 1 µGal. For Maule Earthquake, only the coseismic signal is detected. Due to the limited dataset, the detection of the coseismic signal is successful but the postseismic signal is not long enough to be detected in Tohoku Earthquake. However, the different filters will affect the magnitude of the gravity change, so the real gravity changes of those four areas are still under debate. Last, EOF can be used for the separation of the earthquake signals. Compared to other geodetic technics the gravity method can detect the signals underground and in the ocean areas. The coseismic and postseismic signals detected by GRACE show underground processes of the earthquakes which can help scientists better understand the earthquake mechanism and will contribute to the earthquake prediction in the future