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GNS Science, Lower Hutt, New Zealand
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- PublicationRestrictedCrustal heterogeneity highlighted by spatial b-value map in theWellington region of New Zealand(2010-10)
; ; ; ; ; ; ;Montuori, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Falcone, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Murru, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Thurber, C.; Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA ;Reyners, M.; GNS Science, Lower Hutt, New Zealand ;Eberhart-Phillips, D.; GNS Science, Lower Hutt, New Zealand and University of California, Davis, CA, USA; ; ; ; ; We map the b-value in the subduction zone of theWellington region, NewZealand, using a high quality earthquake catalogue relocated with a 3-D seismic velocity model, consisting of 50 314 events that occurred between 1990 and 2005. In order to investigate heterogeneity in the crust of the overlying plate and in the upper plane of the Wadati–Benioff Zone (WBZ), we analyse a series of cross-sections perpendicular to the strike of the subduction zone. We calculate the b-values selecting events with magnitude of completeness ≥2.4 and depth ≤65 km and projecting the seismicity within 20 km on each side of the cross-sectional planes. We observe areas of high b-value (∼1.7) near the plate interface and regions of low b-value anomalies are detected both in the WBZ in the northwest region below 40 km depth and in the overlying plate in the northern South Island at 10 km depth. The anomalies are statistically significant based on Utsu’s p-test and the bootstrap method and are not data processing method or parameter dependent. We compare the b-value distribution with previously determined 3-D distributions of Vp, Vp/Vs andQp from seismic tomography. This comparison suggests that material inhomogeneity, caused by fluid filled cracks resulting from dehydration of the subducted slab and subducted sediments, is the predominant cause of b-value variation in the shallow part of this subduction zone. Our observations are consistent with a previously proposed conceptual model that fluid distribution in the shallow part of this subduction zone is controlled by the permeability of geological terranes in the overlying plate.386 42 - PublicationOpen AccessOn the Forecasting Horizon of Seismicity Models(2007-05-31)
; ;Rhoades, D.; GNS Science, Lower Hutt, New Zealand; ; ; ; ;Cocco, Massimo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Console, Rodolfo; INGV, Rome, Italy ;Wiemer, Stefan; ETH, Zurich, Switzerland; ; On the Forecasting Horizon of Seismicity Models102 159 - PublicationOpen AccessHighlights from the First Ten Years of the New Zealand Earthquake Forecast Testing CenterThe Collaboratory for the Study of Earthquake Predictability (CSEP) is a global cyberinfrastructure for prospective evaluations of earthquake forecast models and prediction algorithms. CSEP’s goals are to improve our understanding of earthquake predictability, advance forecasting model development, test key scientific hypotheses and their predictive power, and improve seismic hazard assessments. Since its inception in California in 2007, the global CSEP collaboration has been conducting forecast experiments in a variety of tectonic settings and at a global scale and now operates four testing centers on four continents to automatically and objectively evaluate models against prospective data. These experiments have provided a multitude of results that are informing operational earthquake forecasting systems and seismic hazard models, and they have provided new and, sometimes, surprising insights into the predictability of earthquakes and spurned model improvements. CSEP has also conducted pilot studies to evaluate ground-motion and hazard models. Here, we report on selected achievements from a decadeof CSEP, and we present our priorities for future activities.
66 167 - PublicationOpen AccessRenewal models and coseismic stress transfer in the Corinth Gulf, Greece, fault system(2013-07)
; ; ; ; ; ; ; ; ; ; ; We model interevent times and Coulomb static stress transfer on the rupture segments along the Corinth Gulf extension zone, a region with a wealth of observations on strong-earthquake recurrence behavior. From the available information on past seismic activity, we have identified eight segments without significant overlapping that are aligned along the southern boundary of the Corinth rift. We aim to test if strong earthquakes on these segments are characterized by some kind of time-predictable behavior, rather than by complete randomness. The rationale for time-predictable behavior is based on the characteristic earthquake hypothesis, the necessary ingredients of which are a known faulting geometry and slip rate. The tectonic loading rate is characterized by slip of 6 mm/yr on the westernmost fault segment, diminishing to 4 mm/yr on the easternmost segment, based on the most reliable geodetic data. In this study, we employ statistical and physical modeling to account for stress transfer among these fault segments. The statistical modeling is based on the definition of a probability density distribution of the interevent times for each segment. Both the Brownian Passage-Time (BPT) and Weibull distributions are tested. The time-dependent hazard rate thus obtained is then modified by the inclusion of a permanent physical effect due to the Coulomb static stress change caused by failure of neighboring faults since the latest characteristic earthquake on the fault of interest. The validity of the renewal model is assessed retrospectively, using the data of the last 300 years, by comparison with a plain time-independent Poisson model, by means of statistical tools including the Relative Operating Characteristic diagram, the R-score, the probability gain and the log-likelihood ratio. We treat the uncertainties in the parameters of each examined fault source, such as linear dimensions, depth of the fault center, focal mechanism, recurrence time, coseismic slip, and aperiodicity of the statistical distribution, by a Monte Carlo technique. The Monte Carlo samples for all these parameters are drawn from a uniform distribution within their uncertainty limits. We find that the BPT and the Weibull renewal models yield comparable results, and both of them perform significantly better than the Poisson hypothesis. No clear performance enhancement is achieved by the introduction of the Coulomb static stress change into the renewal model.230 56 - PublicationRestrictedComparative performance of time-invariant, long-range and short-range forecasting models on the earthquake catalogue of Greece(2006)
; ; ; ; ; ; ;Console, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rhoades, D. A.; Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand ;Murru, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Evison, F. F.; Institute of Geophysics, School of Earth Sciences, Victoria University of Wellington, Wellington, New Zealand. ;Papadimitriou, E. E.; Geophysics Department, University of Thessaloniki, Thessaloniki, Greece. ;Karakosta, V. G.; Geophysics Department, University of Thessaloniki, Thessaloniki, Greece.; ; ; ; ; Time-invariant, long-range, and short-range forecasting models were fitted to the earthquake catalogue of Greece for magnitudes 4.0 and greater to optimize their ability to forecast events of magnitude 6.0 and greater in the period 1966–1980. The models considered were stationary spatially uniform and spatially varying Poisson models, a long-range forecasting model based on the precursory scale increase phenomenon with every earthquake regarded as a precursor according to scale, and epidemic type short-range forecasting models with spatially uniform and spatially varying spontaneous seismicity. Each of the models was then applied to the catalogue for 1981–2002, and their forecasting performance was compared using the log likelihood statistic. The long-range forecasting model performed substantially better than the time-invariant models, and the short-range forecasting models performed substantially better again. The results show that the information value to be gained from modeling temporal and spatial variation of earthquake occurrence rate, at both long and short range, is much greater than can be gained from modeling spatial variation alone.252 29 - PublicationOpen AccessPrecursory scale increase and long-term seismogenesis in California and Northern Mexico(2002)
; ; ;Evison, F.; Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand ;Rhoades, D.; Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand; A sudden increase in the scale of seismicity has occurred as a long-term precursor to twelve major earthquakes in California and Northern Mexico. These include all earthquakes along the San Andreas system during 1960-2000 with magnitude M 6.4. The full list is as follows: Colorado Delta, 1966, M 6.3; Borrego Mt., 1968, M 6.5; San Fernando, 1971, M 6.6; Brawley, 1979, M 6.4; Mexicali, 1980, M 6.1; Coalinga, 1983, M 6.7; Superstition Hills, 1987, M 6.6; Loma Prieta, 1989, M 7.0; Joshua Tree, 1992, M 6.1; Landers, 1992, M 7.3; Northridge, 1994, M 6.6; Hector Mine, 1999, M 7.1. Such a Precursory Scale Increase () was inferred from the modelling of long-term seismogenesis as a three-stage faulting process against a background of self-organised criticality. The location, onset-time and level of are predictive of the location, time and magnitude of the future earthquake. Precursory swarms, which occur widely in subduction regions, are a special form of ; the more general form is here shownto occur frequently in a region of continental transform. Other seismicity precursors, including quiescence and foreshocks, contribute to or modulate the increased seismicity that characterises . The area occupied by is small compared with those occupied by the seismicity precursors known as AMR, M8 and LURR. Further work is needed to formulate as a testable hypothesis, and to carry out the appropriate forecasting tests.151 321 - PublicationRestrictedThe Collaboratory for the Study of Earthquake Predictability: Achievements and Priorities(2018)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ; ; ;; ; ;The Collaboratory for the Study of Earthquake Predictability (CSEP) is a global cyberinfrastructure for prospective evaluations of earthquake forecast models and prediction algorithms. CSEP’s goals are to improve our understanding of earthquake predictability, advance forecasting model development, test key scientific hypotheses and their predictive power, and improve seismic hazard assessments. Since its inception in California in 2007, the global CSEP collaboration has been conducting forecast experiments in a variety of tectonic settings and at a global scale and now operates four testing centers on four continents to automatically and objectively evaluate models against prospective data. These experiments have provided a multitude of results that are informing operational earthquake forecasting systems and seismic hazard models, and they have provided new and, sometimes, surprising insights into the predictability of earthquakes and spurned model improvements. CSEP has also conducted pilot studies to evaluate ground-motion and hazard models. Here, we report on selected achievements from a decade of CSEP, and we present our priorities for future activities.92 2 - PublicationRestrictedThe Forecasting Skill of Physics‐Based Seismicity Models during the 2010–2012 Canterbury, New Zealand, Earthquake Sequence(2018)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ; ;The static coulomb stress hypothesis is a widely known physical mechanism for earthquake triggering and thus a prime candidate for physics-based operational earthquake forecasting (OEF). However, the forecast skill of coulomb-based seismicity models remains controversial, especially compared with empirical statistical models. A previous evaluation by the Collaboratory for the Study of Earthquake Predictability (CSEP) concluded that a suite of coulomb-based seismicity models were less informative than empirical models during the aftershock sequence of the 1992 Mw 7.3 Landers, California, earthquake. Recently, a new generation of coulomb-based and coulomb/statistical hybrid models were developed that account better for uncertainties and secondary stress sources. Here, we report on the performance of this new suite of models compared with empirical epidemic-type aftershock sequence (ETAS) models during the 2010–2012 Canterbury, New Zealand, earthquake sequence. Comprising the 2010 M 7.1 Darfield earthquake and three subsequent M ≥ 5:9 shocks (including the February 2011 Christchurch earthquake), this sequence provides a wealth of data (394 M ≥ 3:95 shocks). We assessed models over multiple forecast horizons (1 day, 1 month, and 1 yr, updated after M ≥ 5:9 shocks). The results demonstrate substantial improvements in the coulomb-based models. Purely physics-based models have a performance comparable to the ETAS model, and the two coulomb/statistical hybrids perform better or similar to the corresponding statistical model. On the other hand, an ETAS model with anisotropic (fault-based) aftershock zones is just as informative. These results provide encouraging evidence for the predictive power of coulomb-based models. To assist with model development, we identify discrepancies between forecasts and observations.65 5 - PublicationOpen AccessDeep supply of volatile-rich high-Mg magmas changes explosivity of Mount Etna eruptions(2006)
; ; ; ; ; ; ;Kamenetsky, V.; ARC Centre of Excellence in Ore Deposits and School of Earth Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia ;Pompilio, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Metrich, N.; Laboratoire Pierre Sue, CNRS-CEA, CE-Saclay, 91191 Gif sur Yvette, France ;Sobolev, A.; Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany and Vernadsky Institute of Geochemistry, Moscow 117975, Russia ;Kuzmin, D.; Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany and Vernadsky Institute of Geochemistry, Moscow 117975, Russia ;Thomas, R.; GeoForschungsZentrum Potsdam, Telegrafenberg B 120, D-14473, Potsdam, Germany; ; ; ; ; The volcanic hazard potential of Mount Etna volcano is presently nourished by long-lasting, powerful eruptions of basaltic magmas coupled with increased seismicity and ground deformation, and the world’s largest discharge of volcanic gases. The current evolutionary cycle of Mount Etna activity is consistent with subduction-related chemical modifications of the mantle source. Arrival of a new mantle-derived magma batch beneath the volcano has been hypothesized, but is still elusive among the erupted products. Here we demonstrate petrological and geochemical affinities between the magmas supplying modern eruptions and high-Mg, fall-stratified (“FS”) basalts ejected violently ~4 Kyr ago. The “FS” primitive magmas (~13 wt% MgO) are characteristically volatile-enriched (at least 3.8 wt% H2O and 3300 ppm CO2), and bear trace element signature of a garnet-bearing, metasomatised source (high Gd/Yb, K/La, U/Nb, Pb/Ce, Ca/Al). They started crystallizing olivine (Fo91), clinopyroxene (Mg# 92.5) and Cr33 spinel deep in the plumbing system (> 5 kb), contributing to the cumulate piles at depth and to differentiated alkaline basalt and trachybasalt magmas in the shallow conduit. Continuous influx of mantle-derived, volatile-rich magmas, such as those that supplied the “FS” fallout, provides a good explanation for major compositional and eruptive features of Mount Etna.240 379 - PublicationOpen AccessModel of long-term seismogenesis(2001-02)
; ; ;Evison, F.; Institute of Geophysics, Victoria University of Wellington, New Zealand ;Rhoades, D.; nstitute of Geological and Nuclear Sciences, Lower Hutt, New Zealand; A three-stage faulting model explains the observed quantitative relations between long-term precursory seismicity, mainshocks and aftershocks. Seismogenesis starts with the formation of a major crack, culminates in the corresponding major fracture and earthquake, and ends with healing. Crack formation is a self-organised critical phenomenon, and shear fracture is a delayed sequel to crack formation. It is postulated that the major crack generates a set of minor cracks, just as, later, the major fracture generates a set of minor fractures. Fracturing of the minor cracks raises the average seismicity level. By Mogi’s uniformity criterion, the major earthquake is delayed until the minor fractures have healed and the stress-field has regained relative uniformity. In accord with the scaling principle, the model applies at all magnitude levels. The size of any given initial crack determines the scale of the ensuing seismogenic process. A graphical technique of cumulative magnitude analysis gives a quantitative representation of the seismicity aspects of the model. Examples are given for large earthquakes in a region of continental collision and a subduction region. The principle of hierarchy is exemplified by the seismogenesis of a M 5.9 mainshock occurring entirely within the precursory stage of a M 7.0 mainshock. The model is capable of accommodating a variety of proposed shorter-term precursory phenomena.129 400
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