Geodetic Strain Rates Research Articles

Seismic potential in Italy from integration and comparison of seismic and geodetic strain rates

Abstract Seismological and geodetic data provide key information about the kinematics and active tectonics of plate margins. Focal solutions enable the determining of the directions in which the current tectonic stress acts when fault rupturing occurs; GPS measurements provide information on the crustal velocity field and on current interseismic strain rates. The comparison of the strain rates resulting from the two datasets provides further insight into how large an area is affected by aseismic deformation, which is a valuable indicator for seismic hazard mitigation and estimation of the seismic potential. In this work, we investigate both seismic and geodetic strain rates and the combined field resulting from the joint inversion of the geodetic and seismic datasets, providing a picture of the overall deformation field and its variation during the last decades. In this way, we try to give an overview of the seismic potential distribution across the Apennines and southern Italy, as a qualitative analysis of space-time variations in the released seismic strain rate, compared to the space-time distribution of the cumulated geodetic strain rate. The results show a variable distribution of the seismic efficiency over Italy. The Southern Apennines shows the greatest seismic potential, highlighting a significantly lower seismicity in the last two decades over an area affected by the highest total strain rates. The Messina Straits and eastern Sicily have a significant seismic potential, together with the Calabrian arc (from the Tindari–Letojanni and central Aeolian islands to the Mt. Pollino area), as a result of seismic gaps with respect to the combined strain rates in the investigated period. This long gap highlights the longer recurrence periods for the strongest earthquakes on this area. The central–northern Apennines and off-shore northern Sicily, show a lower seismic potential than central–southern Apennines, probably due to the more recent seismicity affecting these areas.

Analysis of the displacement of geodetic stations during the Emilia seismic sequence of May 2012

<span style="font-family: Times New Roman; font-size: small;"> </span><span style="font-family: Times New Roman;"><span style="font-size: small;"><span style="font-family: Calibri; font-size: x-small;"> </span></span><p>The two events of Mw 6.11 and 5.96 [EMERGEO Working Group 2012, this volume] that took place on May 20 and 29, 2012, respectively, in the Po Plain, and the associated seismic sequence, represent the response of the brittle upper crust (hypocentral depth ca. 10 km) to the compressive stress in the outer Apennine Arc. Kinematically, the motion of the Apennines that has led to a compressional regime in the Po Plain can be represented as a counterclockwise rotation, as demonstrated by the shortening of the transalpine baselines, with a rate that decreases going west [Caporali and Martin 2000]. The compressive stress field is known from borehole breakout data [Pierdominici and Heidbach 2012] and it agrees with the principal directions of the strain rate derived from global positioning system (GPS) data. The geodetic strain rate for seismic zone 912 (Dorsale Ferrarese, according to Meletti et al. [2008]) is 92.86 ±0.04 nstrain/yr, which is a relatively high value [Caporali et al. 2011]. On a more local scale, the Mirandola fault is described in the Database of Individual Seismic Sources (DISS; http://diss.rm.ingv.it/) under the ID ITIS107 as a possible individual source, and it has a position, strike, dip, size and expected maximum magnitude [Burrato et al. 2003, Carminati et al. 2010, Scrocca et al. 2007] that are very close to the main events of the 2012 sequence. Several permanent GPS stations were in activity in the area. Using ultrarapid international Global Navigation Satellite Systems (GNSS) Service (IGS) orbits and the Bernese BSW 5.0 software [Dach et al. 2007] at our computing facility, a fast solution for the coseismic displacement was published on the May 21, 2012, and on the May 30, 2012, for the events of May 20 and 29, 2012, respectively. The largest signal was about 2 cm in the North direction at the station SGIP (San Giovanni in Persiceto), which was relatively consistent with the fault-plane solution [Devoti 2012, this volume]. In this study, we present more detailed estimates of the coseismic offsets at several other stations in the area, including a kinematic solution at 30 s temporal resolution. The coseismic displacements are inverted using the Okada [1985] model and a preliminary model of the two faults is obtained for each of the two main events, taking into account the available synthetic aperture radar (SAR) data. […]</p><p class="MsoNormal" style="margin: 0cm 0cm 10pt; text-align: justify; line-height: normal;"><span style="font-family: Calibri; font-size: x-small;"><br /></span></p><span style="font-size: small;"> </span></span>

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

Earthquakes deliver in few seconds the elastic energy accumulated in hundreds of years. Where and when will be the next earthquake remains a difficult task due to the chaotic behaviour of seismicity and the present lack of available tools to measure the threshold of the crustal strength.However, the analysis of the background strain rate in Italy and the comparison with seismicity shows that larger earthquakes occur with higher probability in areas of lower strain rate. We present a statistical study in which a relationship linking the earthquake size (magnitude) and the total strain rate (SR) is found. We combine the information provided by the Gutenberg–Richter law (GR) of earthquake occurrence and the probability density distribution of SR in the Italian area. Following a Bayesian approach, we found a simple family of exponential decrease curves describing the probability that an event of a given size occurs within a given class of SR. This approach relies on the evidence that elastic energy accumulates in those areas where faults are locked and the SR is lower. Therefore, in tectonically active areas, SR lows are more prone to release larger amount of energy with respect to adjacent zones characterised by higher strain rates. The SR map of Italy, compared with 5years seismicity supports this result and may become a powerful tool for identifying the areas more prone to the next earthquakes.

Static stress drop as determined from geodetic strain rates and statistical seismicity

[1] Two critical items in the energetic budget of a seismic province are the strain rate, which is measured geodetically on the Earth's surface, and the yearly number of earthquakes exceeding a given magnitude. Our study is based on one of the most complete and recent seismic catalogs of Italian earthquakes and on the strain rate map implied by a multiyear velocity solution for permanent GPS stations. For each of 36 homogeneous seismic zones we use the appropriate Gutenberg-Richter relation, which is based on the seismicity catalog, to estimate a seismic strain rate, which is the strain rate associated with the mechanical work due to a coseismic displacement. We show that for each seismic zone, the volume storing most of the elastic energy associated with the long-term deformation, and hence the seismic strain rate, is inversely proportional to the static stress drop. The GPS-derived strain rate for each seismic zone limits the corresponding seismic strain rate, and an upper bound for the average stress drop is estimated. We show that the implied regional static stress drop varies from 0.1 to 5.7 MPa for catalog earthquakes in the moment magnitude range [4.5–7.3]. The stress drop results are independent of the regional a and b parameters and heat flow but are very sensitive to the assumed maximum magnitude of a seismic province. The data do not rule out the hypothesis that the stress drop positively correlates with the time elapsed after the largest earthquake recorded in each seismic zone.

Coexisting tectonic settings: the example of the southern Tyrrhenian Sea

We performed geodetic strain rate analyses in southern Italy, using new GPS velocities. Two-dimensional strain and rotation rate fields were estimated and results show that most of the shortening is distributed in the northern Sicily offshore. Extension becomes more evident and comparable with shortening on the eastern side of the same margin, and greater in the eastern Sicily offshore. Principal shortening and extension rate axes are consistent with long-term geological features: seismic reflection profiles show both active compressive and extensional faults affecting Pleistocene strata. We show evidence for contemporaneous extension and transtension in the Cefalu Basin. Combining geodetic data and geological features point to the coexistence of independent geodynamic processes, i.e., the active E–W backarc spreading in the hangingwall of the Apennines subduction zone and shortening along the southern margin of the Tyrrhenian backarc basin operated by the NNW-motion of Africa relative to Eurasia.

The dynamics of the eastern Mediterranean and eastern Turkey

SUMMARY In this study we investigate the dynamics of the region that includes Greece, the Aegean Sea and Asia Minor. In a least-squares inversion we solve for a continuous strain rate field, and corresponding velocity field, that satisfies 872 GPS data. The estimate of the geodetic strain rate field provides constraints for our dynamic analysis. Next, we separately solve the depth integrated 3-D force balance equations for depth-integrated deviatoric stresses within the lithosphere, in which body force input comes from differences in vertically integrated vertical stress, or differences in gravitational potential energy per unit area (GPE). These GPE estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere. Further, we investigate the sensitivity of our stress field solutions by using two different crustal structure models: one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the Crust 2.0 model. In an iterative least-squares inversion we then solve for stress field boundary conditions that, when added to the contribution of deviatoric stresses associated with GPE differences, provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis. Robust features that arise from the boundary condition solution are NNE forcing along the southern boundary east of about 33° E (0.5–1.2 × 1012 N m−1), with a rapid anticlockwise rotation of forces to the west of this, along with an outward pulling force (∼0.4 × 1012 N m−1) directed SSW along the entire Hellenic Arc segment. This force system along the Hellenic Arc can be interpreted as a result of slab rollback. The total depth integrated 3-D deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region, with vertically integrated stress magnitudes of order 0.5–2.5 × 1012 N m−1. We use constraints from derived stress magnitudes, together with GPS-defined scalar values of strain rate magnitude, to define bulk effective viscosities of the lithosphere. Depth-averaged effective viscosities for the entire lithosphere are high within the Black Sea, of order 0.7–3 ×1023 Pa-s, relative to surrounding continental lithosphere. North Anatolian shear zone, northern Aegean Sea and Gulf of Corinth are characterized by low depth averaged viscosities of order 1–5 ×1021 Pa-s. Deviatoric stresses from GPE differences and boundary condition effects combine in surprising ways in some regions, resulting in near total stress cancellation in areas such as the southern Aegean Sea and portions of the central Anatolian block. GPE differences combine with boundary condition effects along the eastern segment of the North Anatolian Fault (NAF) in a way that is compatible with the hypothesis that motion on the NAF was facilitated by slab detachment beneath East Anatolia and dynamic uplift of East Anatolian Plateau. In general, GPE differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field. The low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere.

A new velocity field for Greece: Implications for the kinematics and dynamics of the Aegean

A new set of geodetic velocities for Greece and the Aegean, derived from 254 survey‐mode and continuous GPS sites, is used to test kinematic and dynamic models for this area of rapid continental deformation. Modeling the kinematics of the Aegean by the rotation of a small number (3–6) of blocks produces RMS misfits of ∼5 mm yr−1 in the southern Aegean and western Peloponnese, indicating significant internal strain within these postulated blocks. It is possible to fit the observed velocities to within 2–3 mm yr−1 (RMS) by models that contain 10 or more blocks, but many such models can be found, with widely varying arrangements of blocks, that fit the data equally well provided that the horizontal dimension of those blocks is not larger than 100–200 km. A continuous field of velocity calculated from the GPS velocities by assuming that strain rates are homogeneous on the scale of ∼120 km fits the observed velocities to better than 2–3 mm yr−1 (RMS), with systematic misfits, representing more localized strain, confined to a region approximately 100 × 100 km in size around the western Gulf of Corinth. This velocity field accounts for the major active tectonic features of Greece and the Aegean, including the widespread north‐south extensional deformation and the distributed strike‐slip deformation in the NE Aegean and western Greece. The T axes of earthquakes are aligned with the principal axes of elongation in the geodetic field, major active normal fault systems are perpendicular to those axes, and ∼90% of the large earthquakes in this region during the past 120 years took place within the areas in which the geodetic strain rate exceeds 30 nanostrain yr−1. These observations suggest that the faulting within the upper crust of the Aegean region is driven by forces that are coherent over a scale that is significantly greater than 100 km. It is likely that those forces arise primarily from differences in gravitational potential energy within the lithosphere of the region.

Strain rates in northwestern Italy from spatially smoothed seismicity

This work presents seismic strain rate maps for the Western Alps and Northern Apennines (northern Italy) as derived from an earthquake catalog collecting both historical and instrumental data. Strain rates are calculated on the basis of the rate of seismic moment release using the Anderson method. Unlike previous applications, which determined the total strain rate associated with specific seismogenic sources, we have employed an innovative zoneless approach based on a spatially smoothed seismicity method. In addition, a Monte Carlo simulation procedure is applied to allow for uncertainty in the input data (e.g., magnitude to moment conversion, seismogenic thickness, maximum earthquake magnitude). Strain rate maps are developed by summing the moments of the earthquakes reported in the catalog and by using two different earthquake recurrence relations. Our results indicate that deformation rates are quite high, ranging from about 2 to 12 × 10−9 yr−1 in the Northern Apennines and from 0.5 to 6 × 10−9 yr−1 in the Western Alps. These values, however, are ∼1 order less than those derived from Global Positioning System measurements, suggesting that a portion of the recent deformation in northwestern Italy is related to aseismic processes. The discrepancies between seismic and geodetic strain rates may also indicate that the record of seismicity may not provide a sufficient time window for assessment of secular rates of moment release (or secular deformation rates) and rates of recurrence of large magnitude earthquakes in the study area.

Geodetic Strain Observations and Return Period of the Strongest Earthquakes of a Given Seismic Source Zone

We present the basis for a method for estimating the return period of large and medium earthquakes that is independent of current deterministic and probabilistic approaches. The two standard techniques of seismic hazard assessment—probabilistic seismic hazard assessment (PSHA) and deterministic seismic hazard assessment (DSHA)—suffer from limited knowledge of seismic prehistory. A further weakness of PSHA is its requirement of homogeneous seismic activity within a seismic zone. Moreover, PSHA and DSHA were developed for seismically active areas and, thus, cannot reliably be used in areas of medium and low activity. In this paper we propose the combined use of geodetic strain rate data and the seismic moment data set determined for past seismic events. This combination represents a new and independent approach to estimation of future seismic activity. Using a modified version of Kostrov’s (Phys Solid Earth 1:23–40, 1974) equation and the catalogue of seismic moments, the minimum return period of the strongest earthquakes of a source area is estimated.

Comparison of geodetic and seismic strain rates in Greece by using a uniform processing approach to campaign GPS measurements over the interval 1994–2000

Abstract In this study we rigorously combine 18 old campaign GPS data sets from Greece covering the period 1994–2000. Although the majority of these old datasets have been analyzed and reported previously, it has not been possible to combine them into a single velocity field and apply strain analysis. Here a uniform, final coordinate solution is given by reprocessing 43 global, long-running International GNSS Service (IGS) sites together with 280 local sites. The 221 daily SINEX files are then combined in a least squares approach and the geodetic horizontal velocity field in ITRF2000 and Europe-fixed reference frame is derived. Two methods are used to compute the geodetic strain rates: (i) discrete estimates within contiguous polygons, and (ii) a continuous curvature surface fitted to the velocity field. The seismic hazard potential can be determined by comparing the geodetic and seismic strain rates. The published 300 year earthquake catalogue best describes the major active tectonic features at the scale of geodetic strain determination. The geodetic strain appears larger than the seismic strain for the majority of the region, suggesting that accumulated strain has not yet been released by earthquakes. The geodetic field is consistent with the detailed constraints implied by the observed orientations of faulting as these are given in the 300-year catalogue. We have shown that with the GPS dataset used in this work and following this processing scheme reasonable results can be obtained comparable with more recent studies, CGPS data and by recent earthquake activity.

Geodetic aspects of seismological phenomena

Seismology is related to many problems of geodesy. The energy production of our planet is rather close to energy consumption of the Earth so that the energy balance can be disturbed significantly by minor processes acting on global scale. From this point of view the effect of tidal triggering of earthquakes is discussed by the study of tidal stress tensor components expressed in spherical system of coordinates. Tidal friction influences through the despinning of the axial rotation the geometrical flattening. This flattening variation causes stresses along the longitude and this phenomenon is closely related to the seismic energy release. Until now there is no unambiguous success to relate changes of the Earth orientation parameters with seismicity. Present-day accuracy of the length of day variations is not sufficient yet to detect spin variation generated by the greatest earthquakes. The polar motion is probably more sensitive to earthquakes and then there is a chance to detect the polar displacements generated by seismic events. In the last section of the present contribution, the strain rates derived from the static seismic moments and from space geodetic observations are compared. Future geodetic strain rate data will be useful in earthquake prediction.

Gravitational potential energy and regional stress and strain rate fields for continental plateaus: Examples from the central Andes and Colorado Plateau

The commonly observed extension in areas of elevated and thickened crust is an expected consequence of having excess gravitational potential energy (GPE) compared to the low GPE of the surrounding crust. While this conceptual model is well founded, it is less clear how well GPE-related stress orientations compare quantitatively to observed stress and strain rate orientations and what any inconsistency tells us about the presence of other competing forces. We estimate the GPE distribution for the central Andes and the greater Colorado Plateau area using topography and crustal thickness variations, respectively, and compare the related stress fields with the World Stress Map as well as with a geodetic strain rate field (for the Colorado Plateau only). In both areas, deviatoric stresses associated with GPE variations alone cannot fully account for the observed deformation rate field. For the central Andes only a combination of deviatoric stresses associated with GPE and relative plate motions can account for the near N–S tensional stress observed in the Peruvian Andes and the margin–normal compressional stress along the eastern Cordillera and sub-Andean fold-and-thrust belt. The observed deformation field around the Colorado Plateau shows E–W extension, largely inconsistent with the deviatoric stresses associated with GPE variations except for the area east of the Rio Grande Rift. The NE–SW oriented stress observed on the southwestern Colorado Plateau is consistent with the orientations of tensional deviatoric stresses associated with GPE variations. We argue that this consistency could be haphazard; stress observations may not reflect the current state of stress due to inherited structure, or could result from the relative high strength of Colorado Plateau that allows for regional GPE variations (and possibly basal shear) to be more significant forces than far-field plate interactions. For the central Andes and Colorado Plateau, stresses associated with GPE variations have a strong influence on the total stress field, and can thus be used to calibrate the overall level of deviatoric stress acting within the lithosphere.

Active crustal deformation in two seismogenic zones of the Pannonian region — GPS versus seismological observations

The seismicity and the associated seismic hazard in the central part of the Pannonian region is moderate, however the vulnerability is high, as three capital cities are located near the most active seismic zones. In our analysis two seismically active areas, the Central Pannonian and Mur-Mürz zones, have been considered in order to assess the style and rate of crustal deformation using Global Positioning System (GPS) and earthquake data. We processed data of continuous and campaign GPS measurements obtained during the years 1991–2007. Velocities relative to the stable Eurasia have been computed at HGRN, CEGRN and EPN GPS sites in and around the Pannonian basin. Uniform strain rates and relative displacements were calculated for the investigated regions. GPS data confirm the mostly left lateral strike slip character of the Mur-Mürz–Vienna basin fault system and suggest a contraction between the eastward moving Alpine-North Pannonian unit and the Carpathians. The computation of the seismic strain rate was based on the Kostrov summation. The averaged unit norm seismic moment tensor, which describes the characteristic style of deformation, has been obtained from the available focal mechanism solutions, whereas the annual seismic moment release showing the rate of the deformation was estimated using the catalogues of historical and recent earthquakes. Our analysis reveals that in the Central Pannonian zone the geodetic strain rate is significantly larger than the seismic strain rate. Based on the weakness of the lithosphere, the stress magnitudes and the regional features of seismicity, we suggest that the low value of the seismic/geodetic strain rate ratio can be attributed to the aseismic release of the prevailing compressive stress and not to an overdue major earthquake. In the Mur-Mürz zone, although the uncertainty of the seismic/geodetic strain rate ratio is high, the seismic part of the deformation seems to be notably larger than in the case of the Central Pannonian zone. These results reflect the different deformation mechanism, rheology and tectonic style of the investigated zones.

Focal mechanism inversion in the Giudicarie–Lessini seismotectonic region (Southern Alps, Italy): Insights on tectonic stress and strain

A set of 41 focal mechanisms (1989–2006) from P-wave first polarities is computed from relocated seismic events in the Giudicarie–Lessini region (Southern Alps). Estimated hypocentral depths vary from 3.1 to 20.8 km, for duration magnitudes ( M D) in the range 2.7–5.1. Stress and strain inversions are performed for two seismotectonic zones, namely G (Giudicarie) and L (Lessini). This subdivision is supported by geological evidence, seismicity distribution, and focal mechanism types. The available number of data (16 in G, 22 in L) does not make possible any further subdivisions. Seismotectonic zones G and L are undergoing different kinematic regimes: thrust with strike-slip component in G, and strike-slip in L. Principal stress and strain axes in each sub-region show similar orientations. The direction of maximum horizontal compressive stress is roughly perpendicular to the thrust fronts along the Giudicarie Belt in zone G, and compatible with right-lateral strike-slip reactivation of the faults belonging to the Schio-Vicenza system in zone L. On the whole, kinematic regimes and horizontal stress orientations show a good fit with other stress data from focal mechanisms and breakouts and with geodetic strain rate axes.

Current crustal deformation in the northern Tien Shan: GPS and seismological data

We study crustal deformation in the northern Tien Shan as recorded in strain rates derived from earthquake and GPS data. Geodetic strain rates indicate general shortening along the N-S component and agree with Quaternary fault slip rates and with the strain field obtained from earthquake mechanisms, all being signature of overall north-south contraction in the region. The GPS strain field changes quickly in time, especially in the W-E direction, and is produced by a joint effect of elastic, plastic, and quasi-plastic deformation. The seismological strain field reflects the effect of external tectonic forces applied to seismogenic crust and the stress change due to crustal heterogeneity and geometry of the study area. Seismological and GPS strain rates carry information of different kinds. The former reflect formation of local structures mainly in the brittle crust, such as a local pull-apart in the center of the Lake Issyk Kul area, whereas the latter provide clues to mechanisms that drive the geological evolution of the mountain terrain as a whole. The current evolution may involve the effect of density instability at the lithosphere-asthenosphere boundary.

3D strength and gravity anomalies of the European lithosphere

Tectonic studies show that intraplate Europe is more active than might be expected from its tectonic setting. We employ integrative analysis of various datasets, which provides new understanding of deformation processes in response to different types of loading. A 3D strength model of the lithosphere, which is based on existing structural, compositional and thermal models of the lithosphere, forms the basis for this study. Boundaries of the crustal layers are determined from existing seismic data. Constraints on the thermal structure of the lithosphere are obtained from heat flow studies and upper mantle seismic tomography. The calculated strength distribution is used to quantify spatial variations in effective elastic plate thickness (EET) of the European lithosphere. A comparison with seismic and geodetic strain rates provides new insights into the localization of intraplate deformation. Another important indication of lithospheric strength is provided by the residual mantle gravity anomalies obtained after removing the crustal contribution from the observed gravity field. We have found significant spatial variations in rigidity within the Central and Western European lithosphere, in contrast with a more uniform strong lithosphere of the East European Platform. These variations are consistent with differences in the density structure of the mantle lithosphere reflected in mantle gravity anomalies. Western Europe is mostly characterized by negative mantle gravity anomalies and low EET values (generally ≤ 20 km), whereas the opposite is true for Eastern Europe. Large differences exist also for specific tectonic units: e.g. a pronounced contrast in lithosphere properties is found between the strong Adriatic plate and the weak Pannonian Basin area, as well as between the Baltic Shield and the North Sea rift system. We demonstrate that the European Cenozoic Rift System (ECRIS), which is characterized by low EET values and negative mantle gravity anomalies, localizes neotectonic deformation manifested by relatively high geodetic and seismic strain rates.

A Bayesian approach to estimating tectonic stress from seismological data

SUMMARY Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.

Statistical analysis of the eigenspace components of the two-dimensional, symmetric rank-two strain rate tensor derived from the space geodetic measurements (ITRF92-ITRF2000 data sets) in central Mediterranean and Western Europe

SUMMARY In the deformation analysis with a 2-D (or planar and horizontal), symmetric rank-two deformation tensor in geosciences (geodesy, geophysics and geology), the eigenspace components of these random deformation tensors (principal components, principal directions) are of focal interest. With the new development of space-geodetic techniques, such as GPS, VLBI, SLR and DORIS, the components of deformation measures (such as the stress or strain tensor, etc.) can be estimated from their highly accurate regular measurement of positions and change rates and analysed by means of the proper statistical testing procedures. In this paper we begin with a review of the results of statistical inference of eigenspace components of the 2-D symmetric, rank-two random tensor (‘random matrix’), that is, the best linear uniformly unbiased estimation (BLUUE) of the eigenspace elements and the best invariant quadratic uniformly unbiased estimate (BIQUUE) of its variance–covariance matrix. Then the geodynamic setting of the Earth and especially the selected investigated region—the central Mediterranean and Western Europe will be discussed. Thirdly, the ITRF sites are selected according to the history and quality of the ITRF realization series, and the related incremental velocities of selected ITRF sites are computed. Fourthly, the methods of derivation for the 2-D geodetic strain rates are introduced in order to obtain these strain rates from the incremental velocities. In the case study, both BLUUE and BIQUUE models as well as related hypothesis tests are applied to the eigenspace components of the 2-D strain rate tensor observations in the area of the central Mediterranean and Western Europe, as derived from the ITRF92 to ITRF2000 sequential station positions and velocities. The interpretation and comparison of these results with the geodynamic feature are followed. Furthermore the statistical inference of the eigenspace components provides us with not only the confidence regions of these estimated, but also the visual presentation of the possible magnitude and the directions of the extension and contraction of the strain rate, which is important for the prediction of the tectonic activity including the possible deformation trend and directions.

Implications of Geodetic Strain Rate for Future Earthquakes, with a Five-Year Forecast of M5 Earthquakes in Southern California

Research Article| January 01, 2007 Implications of Geodetic Strain Rate for Future Earthquakes, with a Five-Year Forecast of M5 Earthquakes in Southern California Zheng-Kang Shen; Zheng-Kang Shen Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) 1Also at: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, 100029 China. Search for other works by this author on: GSW Google Scholar David D. Jackson; David D. Jackson Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) Search for other works by this author on: GSW Google Scholar Yan Y. Kagan Yan Y. Kagan Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) Search for other works by this author on: GSW Google Scholar Author and Article Information Zheng-Kang Shen 1Also at: State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing, 100029 China. Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) David D. Jackson Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) Yan Y. Kagan Department of Earth and Space Sciences University of California-Los Angeles Los Angeles, California 90095-1567 USA zshen@ess.ucla.edu (Z.-K.S.) djackson@ucla.edu (D.D.J.) kagan@ess.ucla.edu (Y.Y.K.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2007 by the Seismological Society of America Seismological Research Letters (2007) 78 (1): 116–120. https://doi.org/10.1785/gssrl.78.1.116 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Zheng-Kang Shen, David D. Jackson, Yan Y. Kagan; Implications of Geodetic Strain Rate for Future Earthquakes, with a Five-Year Forecast of M5 Earthquakes in Southern California. Seismological Research Letters 2007;; 78 (1): 116–120. doi: https://doi.org/10.1785/gssrl.78.1.116 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 SocietySeismological Research Letters Search Advanced Search Despite great efforts made by geoscientists, precise earthquake prediction still remains illusive. It has become a growing consensus in the recent years that the earthquake process is partially stochastic, and it is more appropriate to take a probabilistic approach to forecasting earthquakes. Because the interseismic, preseismic, and postseismic processes are considered to be mechanically different, different stochastic models may have to be adopted for earthquake forecast models during these different time periods in an earthquake cycle. In this study we attempt to develop a probabilistic earthquake forecast model of intermediate to long times during the interseismic time period, constrained by... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Statistical analysis of geodetic deformation (strain rate) derived from the space geodetic measurements of BIFROST Project in Fennoscandia

Abstract In the deformation analysis in geosciences (geodesy, geophysics and geology), we are often confronted with the problem of a two-dimensional (or planar and horizontal), symmetric rank-two deformation tensor. Its eigenspace components ( principal components , principal direction ) play an important role in interpreting the geodetic phenomena like coseismic/postseismic deformation, plate motions and plate deformations among others. With the new space geodetic techniques, such as GPS, VLBI, SLR and DORIS, positions and change rates of network stations can be accurately determined from the regular measurement campaign, which is acknowledged as an accurate and reliable source of information in Earth deformation studies. This fact suggests that the components of deformation measures (such as the stress or strain tensor, etc.) can be estimated from the highly accurate geodetic data and analyzed by means of the proper statistical testing procedures. While station velocity parameters demonstrate relative motions among stations, strain rate parameters show the in situ strain rate concentration which is directly connected to local stress rate concentration and possibly also to seismic hazard potentials. Therefore, the strain analysis can be considered as a basis of a dynamic model whereas the classical deformation analysis is similar to a kinematic model. We begin with a discussion of the geodynamic setting of the selected investigated region: Fennoscandia. Then the space geodetic observations in the frame of the BIFROST Project are introduced. Thirdly, the methods of deriving the two-dimensional geodetic strain rates tensor are introduced and applied to derive the strain rates from the surface residual velocities, which are based on the Finite-Element-Method (FEM). In the case studies, the strain rates tensors in Fennoscandia and West Europe and the variance–covariances of their eigenspace components are derived. Further detailed analysis of the results is also performed with respect to geodynamical and statistical aspects.