Search

The Seismic hazard study was carried out for Maharashtra state, Bombay (Latitude 18.940 N, Longitude 72.840 E). In the present study the geological fault is known as West coast fault and Son Narmada Faults were studied and used for the earthquake simulation, extended finite fault method originally FINSIM given by M. Atkinson (1998), was used to simulate an earthquake of 6.5 Mw. The soil classification was carried out by the Shear wave velocity and the relation between Shear wave velocity and SPT valves were also recommended by Sumedh Y. Mhaske (2011), since the Mumbai has been formed by the conglomeration of various islands which has come together to form a single landmass. The soil investigation suggested that Most of the region comes under the Class D and C for the worst case simulation we have used the site class D. The peak ground accelerations (PGA) vary from 0.03g to 0.133 g. While coming to zonal area IS1893:2002 still consider the Mumbai city under zone III with the Z value of 0.16 and the result have been compared with the analysis done by many researchers in the same area. [ABSTRACT FROM AUTHOR]

The application of a physics-based earthquake simulation algorithm to the Central Apennines, where the 2016-2017 seismic sequence occurred, allowed the compilation of a synthetic seismic catalogue lasting 100 kyr, and containing more than 500 000 M ≤ 4.0 events, without limitations in terms of completeness, homogeneity and time duration. This simulator is based on an algorithm constrained by several faulting and source parameters. The seismogenicmodel upon which we applied the simulator code, was derived from the Database of Individual Seismogenic Sources including all the fault systems that are recognized in the Central Apennines. The application of our simulation algorithm provides typical features in time, space and magnitude behaviour of the seismicity, which are comparable with the observations. These features include long-term periodicity and a realistic earthquake magnitude distribution. The statistical distribution of earthquakes withM≤6.0 on single faults exhibits a fairly clear pseudo-periodic behaviour, with a coefficient of variation Cv of the order of 0.4-0.8.We found in our synthetic catalogue a clear trend of long-term acceleration of seismic activity preceding M ≤ 6.0 earthquakes and quiescence following those earthquakes. Lastly, as an example of a possible use of synthetic catalogues, an attenuation law was applied to all the events reported in the synthetic catalogue for the production of maps showing the exceedance probability of given values of peak acceleration in the investigated territory. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of verifying earthquake simulators with observed data. Earthquake simulators are a class of computational simulations which attempt to mirror the topological complexity of fault systems on which earthquakes occur. In addition, the physics of friction and elastic interactions between fault elements are included in these simulations. Simulation parameters are adjusted so that natural earthquake sequences are matched in their scaling properties. Physically based earthquake simulators can generate many thousands of years of simulated seismicity, allowing for a robust capture of the statistical properties of large, damaging earthquakes that have long recurrence time scales. Verification of simulations against current observed earthquake seismicity is necessary, and following past simulator and forecast model verification methods, we approach the challenges in spatial forecast verification to simulators; namely, that simulator outputs are confined to the modeled faults, while observed earthquake epicenters often occur off of known faults. We present two methods for addressing this discrepancy: a simplistic approach whereby observed earthquakes are shifted to the nearest fault element and a smoothing method based on the power laws of the epidemic-type aftershock (ETAS) model, which distributes the seismicity of each simulated earthquake over the entire test region at a decaying rate with epicentral distance. To test these methods, a receiver operating characteristic plot was produced by comparing the rate maps to observed $$m>6.0$$ earthquakes in California since 1980. We found that the nearest-neighbor mapping produced poor forecasts, while the ETAS power-law method produced rate maps that agreed reasonably well with observations. [ABSTRACT FROM AUTHOR]

In this manuscript, we introduce a framework for developing earthquake forecasts usingVirtual Quake (VQ), the generalized successor to the perhaps better known Virtual California (VC) earthquake simulator. We discuss the basic merits and mechanics of the simulator, and we present several statistics of interest for earthquake forecasting. We also show that, though the system as a whole (in aggregate) behaves quite randomly, (simulated) earthquake sequences limited to specific fault sections exhibit measurable predictability in the form of increasing seismicity precursory to large m>7 earthquakes. In order to quantify this, we develop an alertbased forecasting metric, and show that it exhibits significant information gain compared to random forecasts. We also discuss the long-standing question of activation versus quiescent type earthquake triggering. We show that VQ exhibits both behaviours separately for independent fault sections, some fault sections exhibit activation type triggering, while others are better characterized by quiescent type triggering. We discuss these aspects of VQ specifically with respect to faults in the Salton Basin and near the El Mayor-Cucapah region in southern California, USA and northern Baja California Norte, Mexico. [ABSTRACT FROM AUTHOR]

A methodology is presented for computing elastic-rebound-based probabilities in an unsegmented fault or fault system, which involves computing alongfault averages of renewal-model parameters. The approach is less biased and more self-consistent than a logical extension of that applied most recently for multisegment ruptures in California. It also enables the application of magnitude-dependent aperiodicity values, which the previous approach does not. Monte Carlo simulations are used to analyze long-term system behavior, which is generally found to be consistent with that of physics-based earthquake simulators. Results cast doubt that recurrenceinterval distributions at points on faults look anything like traditionally applied renewal models, a fact that should be considered when interpreting paleoseismic data. We avoid such assumptions by changing the "probability of what'' question (from offset at a point to the occurrence of a rupture, assuming it is the next event to occur). The new methodology is simple, although not perfect in terms of recovering long-term rates in Monte Carlo simulations. It represents a reasonable, improved way to represent first-order elastic-rebound predictability, assuming it is there in the first place, and for a system that clearly exhibits other unmodeled complexities, such as aftershock triggering. [ABSTRACT FROM AUTHOR]

Interconnected networks of faults and veins filled with hydrothermal minerals such as zeolite are widespread in many orogenic terrains. These fractures commonly form at relatively low temperatures (e.g. <200 °C) late in the tectonic history and represent significant phases of fluid flow and mineralisation during exhumation. Zeolite-bearing fractures spatially associated with the Gole Larghe Fault Zone in the Southern Italian Alps are preserved along an interconnected network of variably orientated pre-existing structures. They show evidence of repeated episodes of hydraulic tensile fracturing and small magnitude (total offsets <5 m) shear displacements. We use geological observations and Coulomb stress modelling to propose that repeated seismogenic rupturing of larger offset faults led to local stress transfer and reactivation of widely distributed smaller pre-existing structures in the wall rocks. The differing orientations of the pre-existing features within what is assumed to have been a single regional stress field led to the simultaneous development of reverse, strike-slip and extensional faults. The kinematic diversity and cyclic nature of the hydraulically-assisted deformation suggest that the mineralised fracture systems represent a geological manifestation of intraplate micro-earthquake clusters associated with fluid migration episodes in the upper crust. Our observations highlight the role of crustal fluids and structural reactivation during earthquakes. [ABSTRACT FROM AUTHOR]

Time-dependent probabilistic seismic hazard assessment requires a stochastic description of earthquake occurrences. While short-term seismicity models are well-constrained by observations, the recurrences of characteristic on-fault earthquakes are only derived from theoretical considerations, uncertain palaeo-events or proxy data. Despite the involved uncertainties and complexity, simple statistical models for a quasi-period recurrence of on-fault events are implemented in seismic hazard assessments. To test the applicability of statistical models, such as the Brownian relaxation oscillator or the stress release model, we perform a systematic comparison with deterministic simulations based on rate- and state-dependent friction, high-resolution representations of fault systems and quasi-dynamic rupture propagation. For the specific fault network of the Lower Rhine Embayment, Germany, we run both stochastic and deterministic model simulations based on the same fault geometries and stress interactions. Our results indicate that the stochastic simulators are able to reproduce the first-order characteristics of the major earthquakes on isolated faults as well as for coupled faults with moderate stress interactions. However, we find that all tested statistical models fail to reproduce the characteristics of strongly coupled faults, because multisegment rupturing resulting from a spatiotemporally correlated stress field is underestimated in the stochastic simulators. Our results suggest that stochastic models have to be extended by multirupture probability distributions to provide more reliable results. [ABSTRACT FROM AUTHOR]

After nucleation, a large earthquake propagates as an expanding rupture front along a fault. This front activates countless fault patches that slip by consuming energy stored in Earth's crust. We simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel The spontaneous evolution of strength, acceleration, and velodty indicates that our experiments are proxies of fault-patch behavior during earthquakes of moment magnitude (Mw) = 4 to 8. We show that seismically determined earthquake parameters (e.g., displacement, ve[odty, magnitude, or fracture energy) can be used to estimate the intensity of the energy release during an earthquake. Our experiments further indicate that high acceleration imposed by the earthquake's rupture front quickens dynamic weakening by intense wear of the fault zone. [ABSTRACT FROM AUTHOR]

We generate synthetic catalogs of seismicity in northern California using a composite simulation. The basis of the simulation is the fault based "Virtual California" (VC) earthquake simulator. Back-slip velocities and mean recurrence intervals are specified on model strike-slip faults. A catalog of characteristic earthquakes is generated for a period of 100 000 yr. These earthquakes are predominantly in the range M = 6 to M = 8, but do not follow Gutenberg-Richter (GR) scaling at lower magnitudes. In order to model seismicity on unmapped faults we introduce background seismicity which occurs randomly in time with GR scaling and is spatially associated with the VC model faults. These earthquakes fill in the GR scaling down to M =4 (the smallest earthquakes modeled). The rate of background seismicity is constrained by the observed rate of occurrence of M > 4 earthquakes in northern California. These earthquakes are then used to drive the BASS (branching aftershock sequence) model of aftershock occurrence. The BASS model is the self-similar limit of the ETAS (epidemic type aftershock sequence) model. Families of aftershocks are generated following each Virtual California and background main shock. In the simulations the rate of occurrence of aftershocks is essentially equal to the rate of occurrence of main shocks in the magnitude range 4 < M < 7. We generate frequencymagnitude and recurrence interval statistics both regionally and fault specific. We compare our modeled rates of seismicity and spatial variability with observation [ABSTRACT FROM AUTHOR]

We calculate near-source broadband (0-10 Hz) seismograms by combining low-frequency three-dimensional (3D) finite-difference seismograms (0-0.5 Hz) computed in a 3D velocity model using site-specific scattering Green's functions for random, isotropic scattering media. The scattering Green's functions are convolved with a slip-rate function to form local scattering operators (scatterograms), which constitute the high-frequency scattered wave field. The low-frequency and high-frequency scatterograms are then combined in the frequency domain to generate broadband waveforms. Our broadband method extends the Mai et al. (2010) approach by incorporating dynamically consistent source-time functions and accounting for finite-fault effects in the computation of the high-frequency waveforms. We used the proposed method to generate broadband ground motions at 44 sites located 5-100 km from the fault, for Mw 7.7 earthquake scenarios (TeraShake) on the southern San Andreas fault, which include north-to-south, south-to-north, and bilateral rupture propagation from kinematic and spontaneous dynamic rupture models. The broadband ground motions computed with the new method are validated by comparing peak ground acceleration, peak ground velocity, and spectral acceleration with recently proposed ground-motion prediction equations (GMPEs). Our simulated ground motions are consistent with the median ground motions predicted by the GMPEs. In addition, we examine overturning probabilities for 18 precariously balanced rock sites (PBR). Our broadband synthetics for the Mw 7.7 TeraShake scenarios show no preferred rupture direction on the southern San Andreas fault but are inconsistent with the existence of PBRs at several of the sites analyzed. [ABSTRACT FROM AUTHOR]

This paper describes refinements to the hybrid broadband ground-motion simulation methodology of Graves and Pitarka (2004), which combines a deterministic approach at low frequencies (f < 1 Hz) with a semistochastic approach at high frequencies (f > 1 Hz). In our approach, fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed, and rise time. The prescribed slip distribution is constrained to follow an inverse wavenumber-squared fall-off and the average rupture speed is set at 80% of the local shear-wave velocity, which is then adjusted such that the rupture propagates faster in regions of high slip and slower in regions of low slip. We use a Kostrov-like slip-rate function having a rise time proportional to the square root of slip, with the average rise time across the entire fault constrained empirically. Recent observations from large surface rupturing earthquakes indicate a reduction of rupture propagation speed and lengthening of rise time in the near surface, which we model by applying a 70% reduction of the rupture speed and increasing the rise time by a factor of 2 in a zone extending from the surface to a depth of 5 km. We demonstrate the fidelity of the technique by modeling the strong-motion recordings from the Imperial Valley, Loma Prieta, Landers, and Northridge earthquakes. [ABSTRACT FROM AUTHOR]

Abstract We investigate properties of earthquake stress drops in simulations of evolving seismicity and stress field on a heterogeneous fault. The model consists of an inherently discrete strike-slip fault surrounded by a 3D elastic half-space. We consider various spatial distributions of frictional properties and analyze results generated by 150-300 model years. In all cases, the self-organized heterogeneous initial stress distributions at the times of earthquake failure lead to stress drops that are systematically lower than those predicted for a homogeneous process. In particular, the large system-sized events have stress drops that are consistently ~25% of predictions based on the average fault strength. The type and amount of assumed spatial heterogeneity on the fault affect the stress-drop statistics of small earthquakes (ML < 5) more than those of the larger events. This produces a decrease in the range of stress drops as the earthquake magnitudes increase. The results can resolve the discrepancy between traditional estimates of stress drops and seismological observations. The general tendency for low stress drops of large events provides a rationale for reducing the statistical estimates of potential ground motion associated with large earthquakes. [ABSTRACT FROM AUTHOR]

We construct source models of two large intraslab earthquakes (the 1993 Kushiro-oki and 1994 Hokkaido Toho-oki earthquakes) along the southern Kurile-Hokkaido arc based on strong motion records; the source models well explain observed broadband strong ground motions. We assume a distribution of rectangular-shaped asperities on a fault plane and apply the empirical Green's function method to the synthesis of strong ground motions from the asperities. The asperity parameters (area and stress drop) are estimated by matching the synthetic waveforms (displacement, velocity, and acceleration time histories) and spectra to the observed ones. Our source models have the following characteristics compared with those of inland and plate-boundary earthquakes having a comparable seismic moment: (1) the total asperity area is much smaller, and (2) the stress drop is extremely high (about 200-400 MPa). These indicate that the large intraslab earthquakes radiate seismic energies from a small area in a short time. This rupture process results in extremely strong radiation of short-period seismic waves. Finally, we confirm a correlation between outer (entire fault size, seismic moment, and short-period level of the acceleration source spectrum) and inner fault parameters (areas and stress drops of asperities) for the two intraslab earthquakes. [ABSTRACT FROM AUTHOR]

The article discusses a report within the issue by J. C. Chang and team on a laboratory earthquake simulation experiment using a spinning flywheel on a frictional testing machine to produce an earthquake-like slip event. The rate of acceleration of the wheel was changed to generate kinetic energy to simulated fault zones. Topics include frictional behavior of slip weakening, the effect of friction velocity on fault mechanics, and the behavior of fault zone gouge particles and powder lubrication in earthquake simulations.