Global Centroid Moment Tensor Research Articles

A Model for Visual Assessment of Fault Plane Solutions and Active Tectonics Analysis Using the Global Centroid Moment Tensor Catalog

In this study, individual fault plane solutions are developed using various methods to improve the understanding of active tectonics on a regional scale. The comparative analysis of a focal mechanism solution (FMS) has not elicited the attention of researchers. Therefore, this study aims (1) to visually analyze the fault plane solution for 20 local faults that are responsible for all the earthquakes that occurred using visualization techniques such as: fault parameters, the linked Bingham method, the ad hoc pressure (P) axis and tension (T) axis method, and the moment tensor method; (2) to identify the best method for FMS; and (3) to understand the active tectonics of a fault population. A comparative analysis of the models is systematically documented to improve the understanding of the methods. An analysis of the overall fault mechanism is conducted for the analytic determination of fault movement using fault population data from the Global Centroid Moment Tensor catalog. The approach used in this work is a newly designed method for analyzing the reliability of various techniques for fault mechanism and overall fault movement research. Findings show that for the fault mechanism analysis, the P and T axes method and the moment tensor method are better than the fault plane solution from the fault parameters and the linked Bingham method based on the input parameters, output information, model outfit, and accuracy. The moment tensor method is one of the best approaches for analyzing fault mechanism because the errors in the nine components used as input data for the modeling are negligible. Meanwhile, the P and T axes method is one of the best techniques for the overall analysis of fault movement. P and T dihedral analysis using Kamb contouring is modeled. It indicates that the overall mechanisms of compression and dilation are features at the NW–SE and E–W directions, respectively. This comprehensive and consistent analysis of the fault mechanism provides an overview of the seismotectonic settings in Sabah, Malaysia.

Modern state of crustal stresses of the Apennine Peninsula and adjacent territories (Central Mediterranean region)

This paper discusses models showing the formation of the Central Mediterranean region and the geodynamic setting of the Apennine Peninsula. Cataclastic analysis is used for a repeated reconstruction of the Central Mediterranean region. The catalogue of earthquake focal mechanisms includes 662 events (3.6≤Mb≤6.5) recorded in the study area from 1977 to 2015 (Global CMT, http://www.globalcmt.org; RCMT, http://rcmt2.bo.ingv.it/index.html; Italian CMT dataset, http://rcmt2.bo.ingv.it/Italydataset.html). The reconstruction yielded the directions of principal stresses (including algebraically maximum and minimum ones), locations of domains differing in geodynamic regime, Lode – Nadai coefficients, and orientation of tangential shear stresses acting from the mantle to the crust. By comparing our results to the published data obtained by M.‐L. Zoback’s method, we have identified differences in the orientations of maximum horizontal compression axes at points where the stress ellipsoid takes on its critical values. It is revealed that the strongest earthquakes (M>6) were generated in the areas characterized by the minimum and average relative stress magnitudes.

The focal depths of the 2008 Panzhihua earthquake sequence and the stress field in the source region

Focal depths of the 2008 MS6.1 Panzhihua earthquake sequence and tectonic stress field in the source area are investigated. Source depths of 24 earthquakes in Panzhihua earthquake sequence with a magnitude M≥3.0 were determined using the seismic depth phase sPL; additionally, the focal depths of 232 earthquakes were measured by fitting the three-component waveforms of the P and S waves. The source depth of the main shock is ~12 km. The majority of the aftershocks with magnitude M≥3.0 occurred in the brittle upper crust at the depths range of 12–18 km. Further, the Source mechanisms of the 232 events around the Panzhihua earthquake source area were determined, and the results show that the earthquakes have predominantly strike-slip mechanisms in the Dianzhong Block, but display complexity of the focal mechanisms outside and near the boundary of the Dianzhong block. The 232 earthquake mechanisms from this study are combined with the solutions from the Global Centroid Moment Tensor (GCMT) catalog to derive 2D stress field. The inversion results show that the Dianzhong block is predominantly under a strike slip faulting regime and the direction of the maximum principal compression σ1 is northwest-southeast (NW-SE)-trending. The distribution is coincide with GPS velocity field. However, orientations of principal stress axes as well as the faulting types change outside and near the Dianzhong block. The results show that the tectonic stress field in the study area is predominantly controlled by the southeast (SE)-trending horizontal movement and clockwise rotation of the Dianzhong block as a result of the eastward movement of eastern Tibetan meeting the old and rigid South China block (SCB). The Panzhihua earthquake ruptured at ~12 km depth where the tectonic stress regime is under the SE-direction horizontal compression and the NE-direction horizontal extension.

Activity of crustal faults and the Xolapa sliver motion in Guerrero\u2013Oaxaca forearc of Mexico, from seismic data

Oblique convergent margins often host forearc slivers separated by the subduction interface and a trench parallel strike-slip fault system in the overriding plate. Mexican oblique subduction setting led to the formation of a forearc sliver and accomodation of part of the slip at the bounding system of strike-slip faults. The Xolapa sliver is, on average, a sim 105-km-wide crustal block located along the coast of Guerrero and Oaxaca states of Mexico, and is limited by a sim 650-km-long La Venta-Chacalapa fault zone. Two types of datasets, local catalog and Global CMT compilation, are used to estimate the motion of the Xolapa sliver using the rigid block model that describes the phenomenon of slip partitioning. According to the results obtained from local and Global CMT catalogs for selected subduction thrust earthquakes, the forearc sliver moves southeastwards with respect to the fixed North America plate at the rate of 10 ± 1 mm/year and 5.6 ± 0.8 mm/year, respectively. These velocities in general agree with the values obtained from long-term GPS observations (5–6 mm/year). The origin of the inconsistency between local and teleseismic estimates is attributed to a difference in the double couple focal mechanism parameters for two types of datasets. Convergence obliquity changes from 10.42{^circ } and the rate of 58 mm/year to 13.29{^circ } at the rate of 68 mm/year along the Guerrero and Oaxaca coast increasing from northwest to southeast; therefore, the Xolapa sliver is supposed to be stretched. However, the slip vector azimuths of thrust subduction earthquakes tend to approach plate convergence vectors southeastwards along the coast; so, we assume that this may produce the forearc block compression.

Time window to constrain the corner value of the global seismic-moment distribution

It is well accepted that, at the global scale, the Gutenberg-Richter (GR) law describing the distribution of earthquake magnitude or seismic moment has to be modified at the tail to properly account for the most extreme events. It is debated, though, how much additional time of earthquake recording will be necessary to properly constrain this tail. Using the global CMT catalog, we study how three modifications of the GR law that incorporate a corner-value parameter are compatible with the size of the largest observed earthquake in a given time window. Current data lead to a rather large range of parameter values (e.g., corner magnitude from 8.6 to 10.2 for the so-called tapered GR distribution). Updating this estimation in the future will strongly depend on the maximum magnitude observed, but, under reasonable assumptions, the range will be substantially reduced by the end of this century, contrary to claims in previous literature.

Impact of The 2004 Sumatra-Andaman Earthquake to The Stress Heterogeneity and Seismicity Pattern in Nothern Sumatra, Indonesia

Sumatra Island is a highly seismic active region due to its close location to the convergent zone between the Indo-Australian and Eurasian plates, and the existence of the Great Sumatran Fault (GSF). These conditions caused the island of Sumatra suffered from hundreds of earthquakes with Mw > 4 per year. Particularly, a 9.0 Mw Sumatra-Andaman 2004 earthquake occured in northern Sumatra which changed the in-situ stress and seismicity pattern. In such case, quantifying the tectonic stress perturbation prior and after 2004 Sumatra-Andaman earthquake is becoming key issue in assessing the seismic hazard. To invert the in-situ stress information in Sumatra, first we identify the fault plane from its auxiliary plane in the focal mechanism solutions using the fault instability criterion. There are 354 focal mechanisms data of earthquake with Mw > 5 and focal depths < 250 km along northern Sumatra Island from 1976 to 2010. This catalogue was compiled by combining the data from Global Centroid Moment Tensor (GCMT) catalogue and the International Seismological Centre (ISC) bulletin. We then divided the focal mechanism catalogue into two parts, i.e. prior and after Sumatra-Andaman 2004 earthquake. An iterative joint inversion is then implemented to estimate the in-situ stress orientation and its magnitude ratio. The in-situ principal stress orientation and magnitude ratio obtained from this study will be used to build a Sumatran stress map and its correlation with the seismicity pattern variations in the region. Our results produce remarkable changes of maximum principal stress orientation after 2004 megathrust earthquakes along the region. As the seismic hazard potential is controlled by stress concentration, the obtained results from this study could also be used further for seismic hazard mitigation in northern Sumatra.

Teleseismic body wave inversion in determining rupture process of Sumbawa doublet earthquake, November 25th, 2007

The rupture patterns of the Sumbawa doublet earthquake that occurred on November 25th, 2007 was estimated using teleseismic body wave inversion. The first event occurred at 16:02:18 UTC with epicenter at 8.292°N and 118.37°E, short after this, the second event occurred at 19:53:08 UTC with epicenter at -8.224°N and 118.467°E. For each event, teleseismic body wave data were retrieved from the Incorporated Research Institutions for Seismology – Data Management Center (IRIS-DMC). The waves were windowed for 70 s which started at 20 s before the P-wave arrival, band-pass filtered between 0. 01 and 0.1 Hz and then integrated into a displacement with a sampling time of 0.5 s. The Green’s function is calculated using the Kikuchi and Kanamori method. The fault geometry is based on the earthquake parameters of the Global Centroid Moment Tensor solution. Strike and dip for first event were 88° and 23°, respectively and those for the second event were 87° and 25°, respectively. The seismic moment (Mo) estimated by the inversion for the first event is 0.617×1019 Nm or equivalent to moment magnitude (Mw) 6.46 with source duration of approximately 55 s. While for the second event, the seismic moment is estimated to be 0.644×1019 Nm (Mw 6.47), with slightly longer source duration. The inversion for both events provided a similar slip pattern. The rupture propagated along the dip direction, and the maximum slip occurred near the hypocenter region. The maximum slip amount for first event and second event were 1.43 m and 1.48 m, respectively.

The stress state of the Sakhalin Island and adjacent territories

The present study presents the results of the stress tensor inversion in the Sakhalin-Island and adjacent territories. The method of cataclastic analysis of discontinuous displacements has been used to perform the stress reconstruction. The stress inversion has been performed on the basis of local focal mechanism solution catalog of earthquakes, NEID and Global CMT Project data. The calculations are carried out at three depths levels (0–6 km, 6–12 km and 12–18 km) for magnitude range (Mw) 3.0–7.0. The results of the stress reconstruction allowed us to obtain the new specific features of the tectonic stress field: orientation of the principal stress axes, stress ratio or Lode-Nadai coefficient and the types of stress (the geodynamic regimes). The tectonic stress field is less stable at depth between 6 and 12 km.

A Seismic Moment Magnitude Scale

Research Article| July 02, 2019 A Seismic Moment Magnitude Scale Ranjit Das; Ranjit Das Corresponding Author aNational Research Center for Integrated Natural Disaster Management, Avenue Vicuña Mackenna 4860, Macul, La Florida, Región Metropolitana Santiago, Chile, ranjit244614@gmail.comeAlso at Departamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile. Search for other works by this author on: GSW Google Scholar Mukat Lal Sharma; Mukat Lal Sharma bEarthquake Engineering Department, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India Search for other works by this author on: GSW Google Scholar Hans Raj Wason; Hans Raj Wason bEarthquake Engineering Department, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India Search for other works by this author on: GSW Google Scholar Deepankar Choudhury; Deepankar Choudhury cDepartment of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India Search for other works by this author on: GSW Google Scholar Gabriel Gonzalez Gabriel Gonzalez dDepartamento de Ciencias Geológicas, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, ChilefAlso at National Research Center for Integrated Natural Disaster Management, Avenue Vicuña Mackenna 4860, Macul, La Florida, Región Metropolitana Santiago, Chile. Search for other works by this author on: GSW Google Scholar Bulletin of the Seismological Society of America (2019) 109 (4): 1542–1555. https://doi.org/10.1785/0120180338 Article history first online: 02 Jul 2019 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Ranjit Das, Mukat Lal Sharma, Hans Raj Wason, Deepankar Choudhury, Gabriel Gonzalez; A Seismic Moment Magnitude Scale. Bulletin of the Seismological Society of America 2019;; 109 (4): 1542–1555. doi: https://doi.org/10.1785/0120180338 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract The aim of obtaining a single scale for earthquake magnitudes has led many studies in the past to either develop relationships among various existing scales or develop an altogether new scale to represent a wide range of magnitudes on a single scale. Although a reliable and standardized estimation of earthquake size is a basic requirement for all tectonophysical and engineering applications, different magnitude scales estimate different values for the same earthquake, thereby making such studies inadequate. The moment magnitude (⁠Mw⁠) scale has been referred to by various researchers as the best scale, one that matches well with the observed surface‐wave magnitudes with Ms≥7.5 at a global level. The formulation and validation of the Mw scale were carried out considering the southern California region for lower and intermediate earthquakes.In this study, an endeavor has been made to extend the moment magnitude scale to include lower and intermediate magnitudes in a global context emphasizing the use of body waves, particularly P waves, in which data are abundant. We first investigate the degree of closeness of Mw values with other observed magnitudes (e.g., Ms and mb⁠) for smaller and intermediate magnitude ranges considering global International Seismological Centre (ISC) and Global Centroid Moment Tensor (CMT) databases. To improve upon the consistency of the Mw scale for a wider range, a uniform generalized seismic moment magnitude scale Mwg=logM0/1.36−12.68⁠, for magnitudes≥4.5⁠, has been developed, considering 25,708 global earthquake events having mb and M0 values from ISC and Global CMT databases, respectively, during the period 1976–2006. The Mwg scale is also valid for 3.5≤mb≤7.0 because the relations between seismic moment and the magnitudes mb and Mwg are same.The greater accuracy of the Mwg scale over the Mw scale at different magnitudes (i.e., mb or Ms⁠) is found to be statistically significant in the range including smaller and intermediate events. The similarity of the Mwg scale is also tested on 394 global seismic radiated energy values collected from Choy and Boatwright (1995). It is observed that 76% of estimated radiated energy values obtained through the Mwg scale show closer agreement (than with Mw⁠) to the observed radiated energy values. Mwg is computed from low‐ and high‐frequency spectra, and because it is consistent for small, intermediate, and large earthquake events, it will play a useful role as an earthquake magnitude estimator for all earthquake related studies. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estimation of the Seismic Moment Rate from an Incomplete Seismicity Catalog, in the Context of the InSight Mission to Mars

We evaluate methods to estimate the global seismic moment rate of a planet from the k >= 1 largest events observed during a limited and possibly short-time span, as can be expected, for example, for lander missions to Mars. The feasibility of the approach is demonstrated with a temporary broadband seismometer that was recording in the Mojave desert, California, for 86 days in 2014, and by application to the Global Centroid Moment Tensor (CMT) catalog, subsets thereof, and a catalog of stable continental regions seismicity. From the largest event observed at Goldstone alone (M-w approximate to 7.9), we estimate the Earth's global moment rate to be 1.03 x 10(22) N . m/yr, whereas an estimation based on the 10 strongest events yields a rate of 5.79 x 10(21) N . m/yr. Summation of 42 yr of Global CMT solutions results in an average of 7.61 x 10(21) N . m/yr. In general, a 2 yr interval of Global CMT solutions is sufficient to estimate the Earth's annual moment rate to within a factor of 5 or better. A series of numerical experiments with more than 560 million synthetic catalogs based on the tapered Gutenberg-Richter distribution shows that the estimation is rather insensitive against an unknown slope of the distribution, and that bias and variance of the estimator depend on the ratio between moment rate and corner moment of the size frequency distribution. Moment rates of published Mars models differ by a factor of 1000 or more. Tests with simulated catalogs show that it will be possible to reject some of these models with data returned by NASA's InSight mission after two years of nominal mission life time.

Modern crustal seismicity in the northern Andean Precordillera, Argentina

The Precordillera in the Andean backarc region of Argentina has a long record of large and damaging earthquakes in the last century. Its northern part is not well known seismically neither its style of deformation. In this work we study modern crustal seismicity occurring in the same epicentral area of the historical 1894 earthquake. That earthquake caused deaths and severe damage even at large distances of about 500 km. Because of the unavailability of instrumental records to study this large earthquake, not many details of its seismic source are known. Our study involves broadband and short period seismic data from modern seismicity to characterise the same epicentral area. We used seismic records from the permanent Argentine network (INPRES) and from two temporary broadband experiments (CHARGE and SIEMBRA). We determine 44 seismic locations and their focal depths which are in the range between 10 and 30 km and magnitudes 1.2 ≤ M ≤ 4. In addition, we obtain 33 focal mechanism solutions for some of these earthquakes using P-wave first motions and amplitude ratios between P and S waves; for the same region, five more moderate earthquakes have been ever observed globally and reported by the Global Centroid Moment Tensor catalogue in the last 55 years. We note that epicentres are mainly distributed in the southern sector of the study region, with a relatively greater concentration in the foothills of the Frontal Andes Cordillera. Focal mechanisms show mainly reverse, and in less proportion strike-slip solutions. Overall these results agree with compression and shortening in an east-west orientation of the Andean northern Precordilleran backarc region.

Duration magnitude estimate from local magnitude for moderate earthquakes in three provinces of Sulawesi

The primary aim of this study is to estimate earthquake duration magnitude Md from local magnitude Ml for a set of seismo-tectonic events in North Sulawesi, Central Sulawesi, and West Sulawesi during 2008-2015 years. The data were collected from Webdc3, comprising datasets of magnitudes in the three regions of interest. The data were firstly used to develop corresponding local magnitudes, after which these magnitudes were analyzed to parameterize duration magnitude. Using a simple parametric equation (adopted from relevant work) directly linked Md to Ml, Md = 1.05Ml - 0.17 + c where c represented a correction factor, we found that the equation is applicable to moderate events considered with no significant difference in the calculated values whether or not c was used. For completeness, we compared the Md values in the three provinces with Mw scales provided by the Global CMT catalogue as the reference. The results show that the obtained values of Md are in good agreement with the magnitude reference of Mw within ± 0.2 units in magnitude. The results suggest that empirical relations between Md and Ml used here are appropriate for rapid and accurate magnitude determination to improve seismic hazard assessment in the three provinces.

Structural interpretation of gravity, topography and seismicity

Abstract Global geophysical observations constrain all theories of terrestrial dynamics. We jointly interpret EGM2008 gravity, RET2014 topography and the Global Centroid Moment Tensor database from a structural point of view. We hypothesize that lateral variations of gravity and topography reflect the scale-dependent competence of rocks. We compare the spectral and spatial characteristics of the observed fields with structural predictions from the mechanics of differential grade-2 (DG-2) materials. The results indicate that these viscoelastic materials are a powerful tool for exploring dynamic processes in the Earth. We demonstrate that the known spectral range of Earth's gravity and topography can be explained by the folding, shear banding, faulting and differentiation of the crust, lithosphere and mantle. We show that the low-amplitude long-wavelength bias apparent in the disturbance field can be explained by perturbations to Earth's overall ellipsoidal shape, induced by internal slab loading of the mantle. We find by examining the directional isotropy of the data that the zonal energy in Earth's gravity disturbance is maximized about an axis coincident with the shape-perturbation minimum. The symmetry of tectonic features about this axis, extending from eastern Borneo to Brazil, and its coincidence with the equator suggest the coupling of current plate motions to true polar wander.

Tsunami Modelling of the 8th September 2017 Mexico Earthquake of M 8.1, Using Two Different Software

On 8th of September 2017, an earthquake of magnitude Mw 8.1 was generated offshore Mexico, Chiapas area, at 04:49 UTC, with a depth of 72 km and the following coordinates: Latitude 15.02 N, Longitude 93.81 W, 98 km away from Pijijiapan (Mexico). The fault plane solution of the event was normal plane. Maximum tsunami waves of 1.1 m were measured at Salina Cruz sea level station, following the earthquake. Tsunami modelling simulations were accomplished using the earthquake’s parameters (location, magnitude, depth) and moment tensor solutions given by 3 different agencies: United States Geological Survey (USGS), German Research Centre for Geosciences (GFZ) and Global Centroid Moment Tensor (GCMT). For every case studied, the affected locations, sea level estimates and maximum wave heights were computed. There are two software used for modelling, the Tsunami Analysis Tool (TAT), provided and developed by the Joint Research Centre, Ispra, Italy and TRIDEC Cloud, provided by the German Research Centre for Geosciences (GFZ), Potsdam, Germany. After analysing the modelling scenarios, a comparison between the results of the two software was accomplished, for the same earthquake parameters. The results show that the parameters of GCMT computed with TAT overestimate those computed with TRIDEC, of maximum 3.9 m wave height at Arista with TAT and 2.46 m with TRIDEC. For the GFZ parameters, the estimates give 3.5 m for Pasito de la Senora with TAT, compared to 1.64 m maximum waves at Puerto Madero with TRIDEC. For the USGS data set, the results are similar, maximum waves of 2.4 m at Pasito de la Senora with TAT, and 2.9 m at Puerto Madero with TRIDEC. The Salina Cruz station, where 1.1 m height waves were measured, gives results only for the simulations ran with TAT, with 1.0 m for the GFZ earthquake parameters, 0.6 m for USGS and 1.4 m for the GCMT parameters.

Regional stress field in Yunnan revealed by the focal mechanisms of moderate and small earthquakes

We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme. Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.

Earthquake relocation using HypoDDMethod to investigate active fault system in Southeast Aceh

Southeast aceh is one of the most seismically region in the Aceh Province because the existence of the subduction zone and Sumatra Fault Zone (SFZ). In this paper, we present the active fault system that derived from the seismicity distribution and focal mechanisms of earthquakes which occurring along the fault system. In this case, we studied the earthquakes that occurred around the Tripa segment along the Sumatran Fault. The Tripa fault is a segmented fault of SFZ, actively moving, and recently generating some earthquake, this seismic activity was made by the impact from accumulated stress on rock. We use earthquake catalogues including P and S arrival times which collected by BMKG. The earthquake locations were relocated by using double difference method (HypoDD) and the focal mechanisms were obtained from GFZ-Postdam and global CMT solution. The 70 events was obtained from bmkg catalog, only 40 succeeded to be relocated using local velocity models. The earthquakes relocation by using double difference method finally provides sharper lineation of seismicity consisting of three earthquake clusters in the research area. The relocation results show the value change in location and depth which more reliable than the earthquake data from catalogue. The focal mechanisms of earthquakes indicate the right lateral earthquakes similar to fault plane solution of the Sumatran Fault.

A 20-yr database (1997-2017) of co-seismic displacements from GPS recordings in the Aegean area and their scaling with Mw and hypocentral distance

We describe and make available a dataset of 64 data points of Global Positioning System (GPS) displacements for significant, shallow earthquakes in Greece during the period 1997-2017. The displacement data can be used by earthquake geologists, engineers and seismologists in an effort to better understand the faulting process, the rupture mechanics, the pattern of ground-motions, and in engineering applications. We include recordings from GNSS networks at near-source to regional distances (2–132 km) for 11 earthquakes between global CMT moment magnitudes (Mw) 5.5 and 6.9. We also model the magnitude scaling properties of peak ground horizontal displacements (PGD and PGD-S) for these events using L1-norm minimisation regression. Our data indicate an almost linear attenuation of seismic strain with distance for this range of seismic magnitudes. We developed a set of relationships based on PGD (in cm) and distance to hypocentre R (in km), which may be used for the rapid estimation of the earthquake magnitude in near real-time.MwPGD = [LOG(PGD) + 8.2849]/(1.6810 – 0.2453LOGR)MwPGD-S = [LOG(PGD-S) + 8.0839]/(1.6793 – 0.2447LOGR)

Prediction of Tsunami Waves by Uniform Slip Models

AbstractConventional tsunami warning systems for local and far‐field areas utilize uniform slip models to predict tsunami waves. The reasons are twofold. First, it is challenging to develop accurate finite‐fault slip models in a short time after an earthquake. Second, tsunami waves are long waves, and hence, the main feature may be predicted without knowing earthquake rupture details. Still, there have been few studies that quantitatively analyze the errors caused by uniform slip models. In this paper, we evaluate if and how such models may be applied for tsunami warnings. For the 2011 Tohoku, 2014 Iquique, and 2015 Illapel tsunamis, we first construct optimum uniform slip models with minimum tsunami waveform misfit and then compare the synthetic tsunami waves with finite‐fault model predictions. Predictions from both type of models match the tsunami data very well, indicating that the prediction errors caused by neglecting slip heterogeneity are insignificant. Further, we derive a common relation between the rupture area and earthquake magnitude. Additionally, the optimum rupture length and width ratio in terms of predicting tsunami waves is determined to be 1 for the three earthquakes. Lastly, we find that moving the uniform slip model to the center of global Centroid Moment Tensor solution produces reasonably small errors in the predicted waveforms. Applying the methodology to three more historic tsunamis shows that uniform slip models can well recover the Deep‐ocean Assessment and Reporting of Tsunamis system recordings, but the rupture center can differ from the global Centroid Moment Tensor solution. Our findings can potentially prompt more reliable tsunami warning strategies for future events.

Structural Geology and the Seismotectonics of the 2004 Great Sumatran Earthquake

AbstractThe paper sets out a method for structural analysis of seismotectonic data using centroid moment tensors and associated hypocenters from the Global Centroid Moment Tensor project, here illustrated for aftershocks from the 2004 great Sumatran earthquake. We show that the Sumatran segments of the megathrust were subject to compression in a direction near to orthogonal with the margin trend, consistent with the effect of relative movement of the adjacent tectonic plates. In contrast, the crust above the Andaman Sea segments was subject to margin‐orthogonal extension, consistent with motion toward the gravitational potential well accumulated due to prior lateral (westward) rollback of the subducting edge of the northward moving Indian plate. Since this potential well is largely defined by topography, this episode of margin‐orthogonal extension is at least in part “gravity driven.” It did not last long. Within 15 months, an earthquake cluster across an Andaman Sea spreading segment showed a return to kinematics driven by relative plate motion. The transition can be explained if fluid activity temporarily reduced basal friction (or effective stress) but then led to healing so that the megathrust once again began to develop friction‐locked segments. The influence of slab rollback is in developing a gravitational potential well facing the megathrust, hence drawing the overriding crust toward it in the immediate postrupture phase while the megathrust is in a weakened state. Plate tectonics dominates during interseismic gaps, once the megathrust heals, and regains frictional resistance.

Using Tsunami Waves Reflected at the Coast to Improve Offshore Earthquake Source Parameters: Application to the 2016 Mw 7.1 Te Araroa Earthquake, New Zealand

AbstractThe Te Araroa earthquake occurred on 2 September 2016 (local time) offshore of the northeastern coast of New Zealand's North Island (Mw 7.1). When this event occurred, ocean bottom pressure gauges (OBPs), installed ~170 km south of the source area, clearly recorded direct tsunami from the source to OBPs (~ −1.5 cm), and tsunami from coastal reflections (~2 cm). We estimate the centroid location that best reproduces the OBP waveforms. When using the direct wave alone, the centroid location is poorly constrained, with a horizontal uncertainty of ~100 km. By combining both direct and reflected tsunami waveforms, we obtain a centroid location near the Global Centroid Moment Tensor centroid (~80 km northeast from the coast) with smaller uncertainty (~40 km). We also estimate the earthquake source dimension (length and width) and found that the models using coastal reflections require a source dimension larger than ~30 km long. Based on the slip distribution obtained by the finite fault inversion, we obtain an energy‐based stress drop ΔσE of 1.0 MPa, consistent with typical earthquake stress drop values. This study shows that the information added by coastal reflected tsunami provides much tighter constraints on the centroid location, source dimension, and stress drop of offshore earthquakes, which is difficult to obtain from the onshore seismic data alone. Future studies should utilize the information provided by coastal reflected waves to improve earthquake source modeling using ocean bottom pressure data.