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Sample records for aftershock sequence model

  1. Estimating the ETAS model from an early aftershock sequence

    NASA Astrophysics Data System (ADS)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2014-02-01

    Forecasting aftershock probabilities, as early as possible after a main shock, is required to mitigate seismic risks in the disaster area. In general, aftershock activity can be complex, including secondary aftershocks or even triggering larger earthquakes. However, this early forecasting implementation has been difficult because numerous aftershocks are unobserved immediately after the main shock due to dense overlapping of seismic waves. Here we propose a method for estimating parameters of the epidemic type aftershock sequence (ETAS) model from incompletely observed aftershocks shortly after the main shock by modeling an empirical feature of data deficiency. Such an ETAS model can effectively forecast the following aftershock occurrences. For example, the ETAS model estimated from the first 24 h data after the main shock can well forecast secondary aftershocks after strong aftershocks. This method can be useful in early and unbiased assessment of the aftershock hazard.

  2. A random effects epidemic-type aftershock sequence model.

    PubMed

    Lin, Feng-Chang

    2011-04-01

    We consider an extension of the temporal epidemic-type aftershock sequence (ETAS) model with random effects as a special case of a well-known doubly stochastic self-exciting point process. The new model arises from a deterministic function that is randomly scaled by a nonnegative random variable, which is unobservable but assumed to follow either positive stable or one-parameter gamma distribution with unit mean. Both random effects models are of interest although the one-parameter gamma random effects model is more popular when modeling associated survival times. Our estimation is based on the maximum likelihood approach with marginalized intensity. The methods are shown to perform well in simulation experiments. When applied to an earthquake sequence on the east coast of Taiwan, the extended model with positive stable random effects provides a better model fit, compared to the original ETAS model and the extended model with one-parameter gamma random effects.

  3. Modelling the 2013 North Aegean (Greece) seismic sequence: geometrical and frictional constraints, and aftershock probabilities

    NASA Astrophysics Data System (ADS)

    Karakostas, Vassilis; Papadimitriou, Eleftheria; Gospodinov, Dragomir

    2014-04-01

    The 2013 January 8 Mw 5.8 North Aegean earthquake sequence took place on one of the ENE-WSW trending parallel dextral strike slip fault branches in this area, in the continuation of 1968 large (M = 7.5) rupture. The source mechanism of the main event indicates predominantly strike slip faulting in agreement with what is expected from regional seismotectonics. It was the largest event to have occurred in the area since the establishment of the Hellenic Unified Seismological Network (HUSN), with an adequate number of stations in close distances and full azimuthal coverage, thus providing the chance of an exhaustive analysis of its aftershock sequence. The main shock was followed by a handful of aftershocks with M ≥ 4.0 and tens with M ≥ 3.0. Relocation was performed by using the recordings from HUSN and a proper crustal model for the area, along with time corrections in each station relative to the model used. Investigation of the spatial and temporal behaviour of seismicity revealed possible triggering of adjacent fault segments. Theoretical static stress changes from the main shock give a preliminary explanation for the aftershock distribution aside from the main rupture. The off-fault seismicity is perfectly explained if μ > 0.5 and B = 0.0, evidencing high fault friction. In an attempt to forecast occurrence probabilities of the strong events (Mw ≥ 5.0), estimations were performed following the Restricted Epidemic Type Aftershock Sequence (RETAS) model. The identified best-fitting MOF model was used to execute 1-d forecasts for such aftershocks and follow the probability evolution in time during the sequence. Forecasting was also implemented on the base of a temporal model of aftershock occurrence, different from the modified Omori formula (the ETAS model), which resulted in probability gain (though small) in strong aftershock forecasting for the beginning of the sequence.

  4. Distribution of the largest event in the critical epidemic-type aftershock-sequence model

    NASA Astrophysics Data System (ADS)

    Vere-Jones, David; Zhuang, Jiancang

    2008-10-01

    This Brief Report corrects and extends the results of Zhuang and Ogata [Phys. Rev. E 73, 046134 (2006)] on the asymptotic behavior of the largest event in the epidemic-type aftershock-sequence model for earthquake occurrence. We show that, in the special case that the underlying branching process is critical, there exists a previously unnoticed mode of behavior, which occurs when the expected family size grows relatively slowly.

  5. Computational Software for Fitting Seismic Data to Epidemic-Type Aftershock Sequence Models

    NASA Astrophysics Data System (ADS)

    Chu, A.

    2014-12-01

    Modern earthquake catalogs are often analyzed using spatial-temporal point process models such as the epidemic-type aftershock sequence (ETAS) models of Ogata (1998). My work introduces software to implement two of ETAS models described in Ogata (1998). To find the Maximum-Likelihood Estimates (MLEs), my software provides estimates of the homogeneous background rate parameter and the temporal and spatial parameters that govern triggering effects by applying the Expectation-Maximization (EM) algorithm introduced in Veen and Schoenberg (2008). Despite other computer programs exist for similar data modeling purpose, using EM-algorithm has the benefits of stability and robustness (Veen and Schoenberg, 2008). Spatial shapes that are very long and narrow cause difficulties in optimization convergence and problems with flat or multi-modal log-likelihood functions encounter similar issues. My program uses a robust method to preset a parameter to overcome the non-convergence computational issue. In addition to model fitting, the software is equipped with useful tools for examining modeling fitting results, for example, visualization of estimated conditional intensity, and estimation of expected number of triggered aftershocks. A simulation generator is also given with flexible spatial shapes that may be defined by the user. This open-source software has a very simple user interface. The user may execute it on a local computer, and the program also has potential to be hosted online. Java language is used for the software's core computing part and an optional interface to the statistical package R is provided.

  6. Applications of the predictability of the Coherent Noise Model to aftershock sequences

    NASA Astrophysics Data System (ADS)

    Christopoulos, Stavros-Richard; Sarlis, Nicholas

    2014-05-01

    A study [1] of the coherent noise model [2-4] in natural time [5-7] has shown that it exhibits predictability. Interestingly, one of the predictors suggested [1] for the coherent noise model can be generalized and applied to the case of (real) aftershock sequences. The results obtained [8] so far are beyond chance. Here, we apply this approach to several aftershock sequences of strong earthquakes with magnitudes Mw ≥6.9 in Indonesia, California and Greece, including the Mw9.2 earthquake that occurred on 26 December 2004 in Sumatra. References. [1] N. V. Sarlis and S.-R. G. Christopoulos, Predictability of the coherent-noise model and its applications, Physical Review E, 85, 051136, 2012. [2] M.E.J. Newman, Self-organized criticality, evolution and the fossil extinction record, Proc. R. Soc. London B, 263, 1605-1610, 1996. [3] M. E. J. Newman and K. Sneppen, Avalanches, scaling, and coherent noise, Phys. Rev. E, 54, 6226-6231, 1996. [4] K. Sneppen and M. Newman, Coherent noise, scale invariance and intermittency in large systems, Physica D, 110, 209 - 222. [5] P. Varotsos, N. Sarlis, and E. Skordas, Spatiotemporal complexity aspects on the interrelation between Seismic Electric Signals and seismicity, Practica of Athens Academy, 76, 294-321, 2001. [6] P.A. Varotsos, N.V. Sarlis, and E.S. Skordas, Long-range correlations in the electric signals that precede rupture, Phys. Rev. E, 66, 011902, 2002. [7] Varotsos P. A., Sarlis N. V. and Skordas E. S., Natural Time Analysis: The new view of time. Precursory Seismic Electric Signals, Earthquakes and other Complex Time-Series (Springer-Verlag, Berlin Heidelberg) 2011. [8] N. V. Sarlis and S.-R. G. Christopoulos, "Visualization of the significance of Receiver Operating Characteristics based on confidence ellipses", Computer Physics Communications, http://dx.doi.org/10.1016/j.cpc.2013.12.009

  7. Predictability in the Epidemic-Type Aftershock Sequence model of interacting triggered seismicity

    NASA Astrophysics Data System (ADS)

    Helmstetter, AgnèS.; Sornette, Didier

    2003-10-01

    As part of an effort to develop a systematic methodology for earthquake forecasting, we use a simple model of seismicity on the basis of interacting events which may trigger a cascade of earthquakes, known as the Epidemic-Type Aftershock Sequence model (ETAS). The ETAS model is constructed on a bare (unrenormalized) Omori law, the Gutenberg-Richter law, and the idea that large events trigger more numerous aftershocks. For simplicity, we do not use the information on the spatial location of earthquakes and work only in the time domain. We demonstrate the essential role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We offer an analytical approach to account for the yet unobserved triggered seismicity adapted to the problem of forecasting future seismic rates at varying horizons from the present. Tests presented on synthetic catalogs validate strongly the importance of taking into account all the cascades of still unobserved triggered events in order to predict correctly the future level of seismicity beyond a few minutes. We find a strong predictability if one accepts to predict only a small fraction of the large-magnitude targets. Specifically, we find a prediction gain (defined as the ratio of the fraction of predicted events over the fraction of time in alarms) equal to 21 for a fraction of alarm of 1%, a target magnitude M ≥ 6, an update time of 0.5 days between two predictions, and for realistic parameters of the ETAS model. However, the probability gains degrade fast when one attempts to predict a larger fraction of the targets. This is because a significant fraction of events remain uncorrelated from past seismicity. This delineates the fundamental limits underlying forecasting skills, stemming from an intrinsic stochastic component in these interacting triggered seismicity models. Quantitatively, the fundamental

  8. Explanation of temporal clustering of tsunami sources using the epidemic-type aftershock sequence model

    USGS Publications Warehouse

    Geist, Eric L.

    2014-01-01

    Temporal clustering of tsunami sources is examined in terms of a branching process model. It previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary Poisson process. The epidemic‐type aftershock sequence (ETAS) branching process model is fitted to tsunami catalog events, using the earthquake magnitude of the causative event from the Centennial and Global Centroid Moment Tensor (CMT) catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated. The ETAS parameters are estimated using the maximum‐likelihood method. The interevent distribution associated with the ETAS model provides a better fit to the data than the Poisson model or other temporal clustering models. When tsunamigenic conditions (magnitude threshold, submarine location, dip‐slip mechanism) are applied to the Global CMT catalog, ETAS parameters are obtained that are consistent with those estimated from the tsunami catalog. In particular, the dip‐slip condition appears to result in a near zero magnitude effect for triggered tsunami sources. The overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that ETAS models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence. The fractional rate of triggered tsunami sources on a global basis is approximately 14%.

  9. Correlation between crustal physical properties and aftershock sequences characteristics

    NASA Astrophysics Data System (ADS)

    Zakharova, O.; Hainzl, S.

    2013-12-01

    The presence of well constrained seismic and GPS data allows to analyze different data sets together. In our work we focus on the complex analyses of the seismic catalogs and a GSP inversions, which will help to connect the aftershock activities to the crustal physical properties. In particular, we are searching for the dependencies between aftershock parameters and seismic coupling, coseismic and postseismic slip on a regional scale. We use the ETAS model for the description of primary and secondary aftershocks. Our analysis is based on the data related to the Chilean Maule (Mw=8.8) and Californian Parkfield (Mw=6.0) aftershock sequences. We have found correlation between the first order of aftershocks and seismic coupling, slip and b-value. Our results give an opportunity for better understanding of the aftershocks appearance.

  10. Modeling aftershocks as a stretched exponential relaxation

    NASA Astrophysics Data System (ADS)

    Mignan, A.

    2015-11-01

    The decay rate of aftershocks has been modeled as a power law since the pioneering work of Omori in the late nineteenth century. Although other expressions have been proposed in recent decades to describe the temporal behavior of aftershocks, the number of model comparisons remains limited. After reviewing the aftershock models published from the late nineteenth century until today, I solely compare the power law, pure exponential and stretched exponential expressions defined in their simplest forms. By applying statistical methods recommended recently in applied mathematics, I show that all aftershock sequences tested in three regional earthquake catalogs (Southern and Northern California, Taiwan) and with three declustering techniques (nearest-neighbor, second-order moment, window methods) follow a stretched exponential instead of a power law. These results infer that aftershocks are due to a simple relaxation process, in accordance with most other relaxation processes observed in Nature.

  11. Magnitude-dependent epidemic-type aftershock sequences model for earthquakes.

    PubMed

    Spassiani, Ilaria; Sebastiani, Giovanni

    2016-04-01

    We propose a version of the pure temporal epidemic type aftershock sequences (ETAS) model: the ETAS model with correlated magnitudes. As for the standard case, we assume the Gutenberg-Richter law to be the probability density for the magnitudes of the background events. Instead, the magnitude of the triggered shocks is assumed to be probabilistically dependent on that of the relative mother events. This probabilistic dependence is motivated by some recent works in the literature and by the results of a statistical analysis made on some seismic catalogs [Spassiani and Sebastiani, J. Geophys. Res. 121, 903 (2016)10.1002/2015JB012398]. On the basis of the experimental evidences obtained in the latter paper for the real catalogs, we theoretically derive the probability density function for the magnitudes of the triggered shocks proposed in Spassiani and Sebastiani and there used for the analysis of two simulated catalogs. To this aim, we impose a fundamental condition: averaging over all the magnitudes of the mother events, we must obtain again the Gutenberg-Richter law. This ensures the validity of this law at any event's generation when ignoring past seismicity. The ETAS model with correlated magnitudes is then theoretically analyzed here. In particular, we use the tool of the probability generating function and the Palm theory, in order to derive an approximation of the probability of zero events in a small time interval and to interpret the results in terms of the interevent time between consecutive shocks, the latter being a very useful random variable in the assessment of seismic hazard.

  12. Magnitude-dependent epidemic-type aftershock sequences model for earthquakes

    NASA Astrophysics Data System (ADS)

    Spassiani, Ilaria; Sebastiani, Giovanni

    2016-04-01

    We propose a version of the pure temporal epidemic type aftershock sequences (ETAS) model: the ETAS model with correlated magnitudes. As for the standard case, we assume the Gutenberg-Richter law to be the probability density for the magnitudes of the background events. Instead, the magnitude of the triggered shocks is assumed to be probabilistically dependent on that of the relative mother events. This probabilistic dependence is motivated by some recent works in the literature and by the results of a statistical analysis made on some seismic catalogs [Spassiani and Sebastiani, J. Geophys. Res. 121, 903 (2016), 10.1002/2015JB012398]. On the basis of the experimental evidences obtained in the latter paper for the real catalogs, we theoretically derive the probability density function for the magnitudes of the triggered shocks proposed in Spassiani and Sebastiani and there used for the analysis of two simulated catalogs. To this aim, we impose a fundamental condition: averaging over all the magnitudes of the mother events, we must obtain again the Gutenberg-Richter law. This ensures the validity of this law at any event's generation when ignoring past seismicity. The ETAS model with correlated magnitudes is then theoretically analyzed here. In particular, we use the tool of the probability generating function and the Palm theory, in order to derive an approximation of the probability of zero events in a small time interval and to interpret the results in terms of the interevent time between consecutive shocks, the latter being a very useful random variable in the assessment of seismic hazard.

  13. Queen Charlotte 2001 Earthquake Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Mulder, T.; Rogers, G. C.

    2012-12-01

    On Oct 12, 2001, an Mw=6.3 earthquake occurred off the Queen Charlotte Islands, BC. It was felt throughout Haida Gwaii (Queen Charlotte Islands) and the adjoining mainland. It generated a small tsunami recorded on Vancouver Island tide gauges. Moment tensor solutions show almost pure thrust faulting. There was a significant aftershock sequence associated with this event. Relocation of the catalogue aftershock sequence with respect to a key calibration event with various subsets of common stations show significant movement in the event locations. The aftershocks define an ~30 degree dipping fault plane.

  14. Sequence-based Parameter Estimation for an Epidemiological Temporal Aftershock Forecasting Model using Markov Chain Monte Carlo Simulation

    NASA Astrophysics Data System (ADS)

    Jalayer, Fatemeh; Ebrahimian, Hossein

    2014-05-01

    Introduction The first few days elapsed after the occurrence of a strong earthquake and in the presence of an ongoing aftershock sequence are quite critical for emergency decision-making purposes. Epidemic Type Aftershock Sequence (ETAS) models are used frequently for forecasting the spatio-temporal evolution of seismicity in the short-term (Ogata, 1988). The ETAS models are epidemic stochastic point process models in which every earthquake is a potential triggering event for subsequent earthquakes. The ETAS model parameters are usually calibrated a priori and based on a set of events that do not belong to the on-going seismic sequence (Marzocchi and Lombardi 2009). However, adaptive model parameter estimation, based on the events in the on-going sequence, may have several advantages such as, tuning the model to the specific sequence characteristics, and capturing possible variations in time of the model parameters. Simulation-based methods can be employed in order to provide a robust estimate for the spatio-temporal seismicity forecasts in a prescribed forecasting time interval (i.e., a day) within a post-main shock environment. This robust estimate takes into account the uncertainty in the model parameters expressed as the posterior joint probability distribution for the model parameters conditioned on the events that have already occurred (i.e., before the beginning of the forecasting interval) in the on-going seismic sequence. The Markov Chain Monte Carlo simulation scheme is used herein in order to sample directly from the posterior probability distribution for ETAS model parameters. Moreover, the sequence of events that is going to occur during the forecasting interval (and hence affecting the seismicity in an epidemic type model like ETAS) is also generated through a stochastic procedure. The procedure leads to two spatio-temporal outcomes: (1) the probability distribution for the forecasted number of events, and (2) the uncertainty in estimating the

  15. Intermediate-term forecasting of aftershocks from an early aftershock sequence: Bayesian and ensemble forecasting approaches

    NASA Astrophysics Data System (ADS)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2015-04-01

    Because aftershock occurrences can cause significant seismic risks for a considerable time after the main shock, prospective forecasting of the intermediate-term aftershock activity as soon as possible is important. The epidemic-type aftershock sequence (ETAS) model with the maximum likelihood estimate effectively reproduces general aftershock activity including secondary or higher-order aftershocks and can be employed for the forecasting. However, because we cannot always expect the accurate parameter estimation from incomplete early aftershock data where many events are missing, such forecasting using only a single estimated parameter set (plug-in forecasting) can frequently perform poorly. Therefore, we here propose Bayesian forecasting that combines the forecasts by the ETAS model with various probable parameter sets given the data. By conducting forecasting tests of 1 month period aftershocks based on the first 1 day data after the main shock as an example of the early intermediate-term forecasting, we show that the Bayesian forecasting performs better than the plug-in forecasting on average in terms of the log-likelihood score. Furthermore, to improve forecasting of large aftershocks, we apply a nonparametric (NP) model using magnitude data during the learning period and compare its forecasting performance with that of the Gutenberg-Richter (G-R) formula. We show that the NP forecast performs better than the G-R formula in some cases but worse in other cases. Therefore, robust forecasting can be obtained by employing an ensemble forecast that combines the two complementary forecasts. Our proposed method is useful for a stable unbiased intermediate-term assessment of aftershock probabilities.

  16. Properties of aftershock sequences in southern California

    NASA Astrophysics Data System (ADS)

    Kisslinger, Carl; Jones, Lucile M.

    1991-07-01

    The temporal behavior of 39 aftershock sequences in southern California, 1933-1988, was modeled by the modified Omori relation. Minimum magnitudes for completeness of each sequence catalog were determined, and the maximum likelihood estimates of the parameters K, p, and c, with the standard errors on each, were determined by the Ogata algorithm. The b value of each sequence was also calculated. Many of the active faults in the region, both strike slip and thrust, were sampled. The p values were graded in terms of the size of the standard error relative to the p value itself. Most of the sequences were modeled well by the Omori relation. Many of the sequences had p values close to the mean of the whole data set, 1.11±0.25, but values significantly different from the mean, as low as 0.7 and as high as 1.8, exist. No correlation of p with either the b value of the sequence or the mainshock magnitude was found. The results suggest a direct correlation of p values is with surface heat flow, with high values in the Salton Trough (high heat flow) and one low value in the San Bernardino Mountains and on the edge of the Ventura Basin (both low heat flow). The large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean, 74 mW/m2. If the hypothesis that aftershock decay rate is controlled by temperature at depth is valid, the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature. Surface heat flow is taken as an indicator of crustal temperature at hypocentral depths, but the effects on heat flow of convective heat transport and variations in near-surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution. The interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault

  17. Zemmouri earthquake rupture zone (Mw 6.8, Algeria): Aftershocks sequence relocation and 3D velocity model

    NASA Astrophysics Data System (ADS)

    Ayadi, A.; Dorbath, C.; Ousadou, F.; Maouche, S.; Chikh, M.; Bounif, M. A.; Meghraoui, M.

    2008-09-01

    We analyze the aftershocks sequence of the Zemmouri thrust faulting earthquake (21 May 2003, Mw 6.8) located east of Algiers in the Tell Atlas. The seismic sequence located during ˜2 months following the mainshock is made of more than 1500 earthquakes and extends NE-SW along a ˜60-km fault rupture zone crossing the coastline. The earthquake relocation was performed using handpicked P and S phases located with the tomoDD in a detailed 3D velocity structure of the epicentral area. Contrasts between velocity patches seem to correlate with contacts between granitic-volcanic basement rocks and the sedimentary formation of the eastern Mitidja basin. The aftershock sequence exhibits at least three seismic clouds and a well-defined SE-dipping main fault geometry that reflects the complex rupture. The distribution of seismic events presents a clear contrast between a dense SW zone and a NE zone with scattered aftershocks. We observe that the mainshock locates between the SW and NE seismic zones; it also lies at the NNS-SSE contact that separates a basement block to the east and sedimentary formations to the west. The aftershock distribution also suggests fault bifurcation at the SW end of the fault rupture, with a 20-km-long ˜N 100° trending seismic cluster, with a vertical fault geometry parallel to the coastline juxtaposed. Another aftershock cloud may correspond to 75° SE dipping fault. The fault geometry and related SW branches may illustrate the interference between pre-existing fault structures and the SW rupture propagation. The rupture zone, related kinematics, and velocity contrasts obtained from the aftershocks distribution are in agreement with the coastal uplift and reflect the characteristics of an active zone controlled by convergent movements at a plate boundary.

  18. Postseismic Pore Pressure Diffusion and its Relationship to Aftershock Sequences

    NASA Astrophysics Data System (ADS)

    Lindman, M.; Lund, B.; Roberts, R.

    2006-12-01

    InSAR measurements of postseismic deformation, water level changes in geothermal wells and time dependent tomography after the two June 2000 M6.5 earthquakes in the south Iceland seismic zone (SISZ) have revealed poroelastic rebound and fluid flow to take place in the postseismic period. This and other examples of pore pressure induced seismicity indicate a strong coupling between fluid flow and the occurrence of earthquakes. It has been suggested that the diffusion of pore pressures induced by a main shock is directly related to the temporal behaviour of aftershocks, described by the well established Omori law. The Omori law describes the rate of aftershocks to decay with time t after a main shock as {dn/dt}={K/(c+t)^p}. The parameter c, reflecting a roughly constant rate during the initial c seconds, is controversial as it is debated whether this behaviour reflects incomplete detection of earthquakes, or, a true description of the physics of the aftershock process. Physical models of aftershock occurrence, including pore pressure diffusion, do suggest that this initial behaviour can indeed be related to the physics of the process. Aftershock sequences within the SISZ indicate that c increases with the magnitude of the main shock. To investigate whether this can be reconciled with postseismic pore pressure diffusion we have modelled the diffusion process following earthquakes of two different magnitudes, M_w=4.6 and M_w=2.2, respectively. We show that the sequences of induced seismicity by these diffusion processes do obey the Omori law, with a magnitude dependency of c that is consistent with the data. We also note that our model captures general features of the spatial variation with time in the aftershock sequences from SISZ that we have studied. An interesting observation in real aftershock sequences is the occurrence of secondary aftershock clusters that results in a temporary rate increase. Our modelling indicates that this feature may be explained by

  19. Triggered Swarms and Induced Aftershock Sequences in Geothermal Systems

    NASA Astrophysics Data System (ADS)

    Shcherbakov, R.; Turcotte, D. L.; Yikilmaz, M. B.; Kellogg, L. H.; Rundle, J. B.

    2015-12-01

    Natural geothermal systems, which are used for energy generation, are usually associated with high seismic activity. This can be related to the large-scale injection and extraction of fluids to enhance geothermal recovery. This results in the changes of the pore pressure and pore-elastic stress field and can stimulate the occurrence of earthquakes. These systems are also prone to triggering of seismicity by the passage of seismic waves generated by large distant main shocks. In this study, we analyze clustering and triggering of seismicity at several geothermal fields in California. Particularly, we consider the seismicity at the Geysers, Coso, and Salton Sea geothermal fields. We analyze aftershock sequences generated by local large events with magnitudes greater than 4.0 and earthquake swarms generated by several significant long distant main shocks. We show that the rate of the aftershock sequences generated by the local large events in the two days before and two days after the reference event can be modelled reasonably well by the time dependent Epidemic Type Aftershock Sequence (ETAS) model. On the other hand, the swarms of activity triggered by large distant earthquakes cannot be described by the ETAS model. To model the increase in the rate of seismicity associated with triggering by large distant main shocks we introduce an additional time-dependent triggering mechanism into the ETAS model. In almost all cases the frequency-magnitude statistics of triggered sequences follow Gutenberg-Richter scaling to a good approximation. The analysis indicates that the seismicity triggered by relatively large local events can initiate sequences similar to regular aftershock sequences. In contrast, the distant main shocks trigger swarm like activity with faster decaying rates.

  20. The Aftershock Risk Index - quantification of aftershock impacts during ongoing strong-seismic sequences

    NASA Astrophysics Data System (ADS)

    Schaefer, Andreas; Daniell, James; Khazai, Bijan; Wenzel, Friedemann

    2016-04-01

    The occurrence and impact of strong earthquakes often triggers the long-lasting impact of a seismic sequence. Strong earthquakes are generally followed by many aftershocks or even strong subsequently triggered ruptures. The Nepal 2015 earthquake sequence is one of the most recent examples where aftershocks significantly contributed to human and economic losses. In addition, rumours about upcoming mega-earthquakes, false predictions and on-going cycles of aftershocks induced a psychological burden on the society, which caused panic, additional casualties and prevented people from returning to normal life. This study shows the current phase of development of an operationalised aftershock intensity index, which will contribute to the mitigation of aftershock hazard. Hereby, various methods of earthquake forecasting and seismic risk assessments are utilised and an integration of the inherent aftershock intensity is performed. A spatio-temporal analysis of past earthquake clustering provides first-hand data about the nature of aftershock occurrence. Epidemic methods can additionally provide time-dependent variation indices of the cascading effects of aftershock generation. The aftershock hazard is often combined with the potential for significant losses through the vulnerability of structural systems and population. A historical database of aftershock socioeconomic effects from CATDAT has been used in order to calibrate the index based on observed impacts of historical events and their aftershocks. In addition, analytical analysis of cyclic behaviour and fragility functions of various building typologies are explored. The integration of many different probabilistic computation methods will provide a combined index parameter which can then be transformed into an easy-to-read spatio-temporal intensity index. The index provides daily updated information about the probability of the inherent seismic risk of aftershocks by providing a scalable scheme fordifferent aftershock

  1. How informative are slip models for aftershock forecasting?

    NASA Astrophysics Data System (ADS)

    Bach, Christoph; Hainzl, Sebastian

    2013-04-01

    Coulomb stress changes (ΔCFS) have been recognized as a major trigger mechanism for earthquakes, in particular aftershock distributions and the spatial patterns of ΔCFS are often found to be correlated. However, the Coulomb stress calculations are based on slip inversions and the receiver fault mechanisms which both contain large uncertainties. In particular, slip inversions are usually non-unique and often differ strongly for the same earthquakes. Here we want to address the information content of those inversions with respect to aftershock forecasting. Therefore we compare the slip models to randomized fractal slip models which are only constrained by fault information and moment magnitude. The uncertainty of the aftershock mechanisms is considered by using many receiver fault orientations, and by calculating ΔCFS at several depth layers. The stress change is then converted into an aftershock probability map utilizing a clock advance model. To estimate the information content of the slip models, we use an Epidemic Type Aftershock Sequence (ETAS) model approach introduced by Bach and Hainzl (2012), where the spatial probability density of direct aftershocks is related to the ΔCFS calculations. Besides the directly triggered aftershocks, this approach also takes secondary aftershock triggering into account. We quantify our results by calculating the information gain of the randomized slip models relative to the corresponding published slip model. As case studies, we investigate the aftershock sequences of several well-known main shocks such as 1992 Landers, 1999 Hector Mine, 2004 Parkfield, 2002 Denali. First results show a huge difference in the information content of slip models. For some of the cases up to 90% of the random slip models are found to perform better than the originally published model, for some other cases only few random models are found performing better than the published slip model.

  2. The (Un)Productivity of the 2014 M6.0 South Napa Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Llenos, A. L.

    2014-12-01

    The M6.0 South Napa mainshock produced fewer aftershocks than expected for a California earthquake of its magnitude, which became apparent a few days into the sequence. In the first 4.5 days, only 59 M≥1.8 aftershocks had occurred, the largest of which was a M3.9 that happened a little over two days after the mainshock. In contrast, during the same time period the 2004 M6.0 Parkfield earthquake had over 220 M≥1.8 aftershocks, 6 of which were M≥4. Here I investigate the aftershock productivity and other sequence statistics of the South Napa sequence and compare it with other M~6 California mainshock-aftershock sequences. By focusing on similar size events, they have similar finite extents within the seismotectonic environment. While the productivities of these sequences vary quite a bit, the b-values of the magnitude-frequency distributions all fall in the 0.6-0.8 range for the northern California sequences, slightly lower than the b-value of ~1 typical of southern California seismicity. Despite the relatively low productivity of the South Napa sequence, I show that the Epidemic-Type Aftershock Sequence (ETAS) model (Ogata, JASA, 1988) describes the sequence well and investigate whether the ETAS model parameters suggest that low-productivity sequences are typical for the region. I also explore how quickly after a mainshock these types of models can capture the low productivity of the sequence. The productivity of a sequence is a critical parameter in determining the aftershock probabilities reported in the days following the mainshock. Therefore, the sooner an accurate representation of the aftershock productivity can be obtained, the sooner more accurate aftershock probability reports can be produced.

  3. Time-dependent Induced Seismicity Rates Described with an Epidemic Type Aftershock Sequence Model at The Geysers Geothermal Field, California

    NASA Astrophysics Data System (ADS)

    Johnson, C. W.; Totten, E. J.; Burgmann, R.

    2015-12-01

    To improve understanding of the link between injection/production activity and seismicity, we apply an Epidemic Type Aftershock Sequence (ETAS) model to an earthquake catalog from The Geysers geothermal field (GGF) between 2005-2015 using >140,000 events and Mc 0.8 . We partition the catalog along a northeast-southwest trending divide, which corresponds to regions of high and low levels of enhanced geothermal stimulation (EGS) across the field. The ETAS model is fit to the seismicity data using a 6-month sliding window with a 1-month time step to determine the background seismicity rate. We generate monthly time series of the time-dependent background seismicity rate in 1-km depth intervals from 0-5km. The average wellhead depth is 2-3 km and the background seismicity rates above this depth do not correlate well with field-wide injected masses over the time period of interest. The auto correlation results show a 12-month period for monthly time series proximal to the average wellhead depths (2-3km and 3-4km) for northwest GGF strongly correlates with field-wide fluid injection masses, with a four-month phase shift between the two depth intervals as fluid migrates deeper. This periodicity is not observed for the deeper depth interval of 4-5 km, where monthly background seismicity rates reduce to near zero. Cross-correlation analysis using the monthly time series for background seismicity rate and the field-wide injection, production and net injection (injection minus production) suggest that injection most directly modulates seismicity. Periodicity in the background seismicity is not observed as strongly in the time series for the southeast field. We suggest that the variation in background seismicity rate is a proxy for pore-pressure diffusion of injected fluids at depth. We deduce that the contrast between the background seismicity rates in the northwest and southeast GGF is a result of reduced EGS activity in the southeast region.

  4. Analysis of the 2012 Oct 27 Haida Gwaii Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Mulder, T.; Brillon, C.; Bentkowski, W.; White, M.; Rosenberger, A.; Rogers, G. C.; Vernon, F.; Kao, H.

    2013-12-01

    The magnitude 7.7 thrust earthquake that occurred on 2012 Oct 28 offshore of Haida Gwaii (formerly the Queen Charlotte Islands), in British Columbia, Canada, produced a rich and on-going aftershock sequence. Ten months of aftershock events are determined from analyst reviewed solutions and automatic detectors and locators. For automated solutions, rotating the waveforms and running P and S wave filters (Rosenberger, 2010) over them produced phase arrivals for an improved catalogue of aftershocks compared to using a traditional signal to noise ratio detector on standard vertical and horizontal component seismograms. The automated aftershock locations from the rotated waveforms are compared to the automated locations from the standard vertical and horizontal waveforms and to analyst locations (which are generally M>2.5). The best of the automated solutions are comparable in quality to analyst solutions and much more numerous making this a viable method of processing extensive aftershock sequences. They outline a region approximately 50 km wide and 100 km long, with the aftershocks in two parallel bands. Most of the aftershocks are not on the rupture surface but are in the overlying or underlying plates. It is thought that this earthquake represents the Pacific plate thrusting underneath the North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault. Due to the one-sided station distribution on land, depth trades off with distance offshore, resulting in poor depth determinations. However, using ocean bottom seismometers deployed early in the aftershock sequence, depth resolution was significantly improved. First motion focal North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault.mechanisms for a portion of the aftershock sequence are compared

  5. Static stress transfer modeling and aftershock statistics for the 2002 Nenana Mountain-Denali Park, Alaska, sequence

    NASA Astrophysics Data System (ADS)

    Anderson, G.; Jones, L. M.; Ji, C.

    2002-12-01

    On October 23, 2002, the Mw 6.7 Nenana Mountain earthquake occurred in central Alaska. While this was a significant event, it became even more interesting as a foreshock to the Mw 7.9 Denali Park mainshock of November 3, 2002, which was the largest earthquake to occur on land in the United States since the 1857 Fort Tejon earthquake in southern California. Using a finite-fault rupture model and the theory of deformation from dislocations in an elastic half-space, we have modeled static Coulomb stress transfer from the Nenana Mountain event to the hypocentral region of the Denali Park event and find that the Nenana Mountain event transferred about 0.05--0.1 MPa (0.5--1 bar) of Coulomb stress to that area, encouraging failure of the later event. We have also computed the combined stress transferred to several large regional faults from the Nenana Mountain and Denali Park events using our Nenana Mountain and Denali Park rupture models. We find that the two main events combined transferred more than 0.05 MPa (0.5 bar) of Coulomb stress to the northern 50 km of the Cross Creek fault, a 150-km-long right-lateral strike slip fault in east-central Alaska, and up to 0.05 MPa of Coulomb stress to the Muldrow segment of the Denali fault, west of the Nenana Mountain rupture. It is worth noting, however, that these faults are nearest to the mainshock rupture and thus most prone to errors in the stress transfer modeling. Other major faults in the region, including the Tonzona, Farewell, and Boss Creek segments of the Denali fault, the Castle Mountain fault near Anchorage, and the Yakataga subduction interface, experienced insignificant static Coulomb stress changes, though dynamic stresses were probably much larger. Although the stress changes from these events are significant, the rates of aftershocks triggered by the Nenana Mountain foreshock and by the Denali Park mainshock are extremely low. We describe the rate of aftershocks with the Reasenberg and Jones formulation for

  6. Statistical estimation of the duration of aftershock sequences

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Christophersen, A.; Rhoades, D.; Harte, D.

    2016-05-01

    It is well known that large earthquakes generally trigger aftershock sequences. However, the duration of those sequences is unclear due to the gradual power-law decay with time. The triggering time is assumed to be infinite in the epidemic type aftershock sequence (ETAS) model, a widely used statistical model to describe clustering phenomena in observed earthquake catalogues. This assumption leads to the constraint that the power-law exponent p of the Omori-Utsu decay has to be larger than one to avoid supercritical conditions with accelerating seismic activity on long timescales. In contrast, seismicity models based on rate- and state-dependent friction observed in laboratory experiments predict p ≤ 1 and a finite triggering time scaling inversely to the tectonic stressing rate. To investigate this conflict, we analyse an ETAS model with finite triggering times, which allow smaller values of p. We use synthetic earthquake sequences to show that the assumption of infinite triggering times can lead to a significant bias in the maximum likelihood estimates of the ETAS parameters. Furthermore, it is shown that the triggering time can be reasonably estimated using real earthquake catalogue data, although the uncertainties are large. The analysis of real earthquake catalogues indicates mainly finite triggering times in the order of 100 days to 10 years with a weak negative correlation to the background rate, in agreement with expectations of the rate- and state-friction model. The triggering time is not the same as the apparent duration, which is the time period in which aftershocks dominate the seismicity. The apparent duration is shown to be strongly dependent on the mainshock magnitude and the level of background activity. It can be much shorter than the triggering time. Finally, we perform forward simulations to estimate the effective forecasting period, which is the time period following a mainshock, in which ETAS simulations can improve rate estimates after the

  7. Statistical monitoring of aftershock sequences: a case study of the 2015 Mw7.8 Gorkha, Nepal, earthquake

    NASA Astrophysics Data System (ADS)

    Ogata, Yosihiko; Tsuruoka, Hiroshi

    2016-03-01

    Early forecasting of aftershocks has become realistic and practical because of real-time detection of hypocenters. This study illustrates a statistical procedure for monitoring aftershock sequences to detect anomalies to increase the probability gain of a significantly large aftershock or even an earthquake larger than the main shock. In particular, a significant lowering (relative quiescence) in aftershock activity below the level predicted by the Omori-Utsu formula or the epidemic-type aftershock sequence model is sometimes followed by a large earthquake in a neighboring region. As an example, we detected significant lowering relative to the modeled rate after approximately 1.7 days after the main shock in the aftershock sequence of the Mw7.8 Gorkha, Nepal, earthquake of April 25, 2015. The relative quiescence lasted until the May 12, 2015, M7.3 Kodari earthquake that occurred at the eastern end of the primary aftershock zone. Space-time plots including the transformed time can indicate the local places where aftershock activity lowers (the seismicity shadow). Thus, the relative quiescence can be hypothesized to be related to stress shadowing caused by probable slow slips. In addition, the aftershock productivity of the M7.3 Kodari earthquake is approximately twice as large as that of the M7.8 main shock.

  8. Evidence for fluid-triggering underlying the year 2014 aftershock sequences in NW Bohemia

    NASA Astrophysics Data System (ADS)

    Hainzl, S.; Fischer, T.; Cermakova, H.; Bachura, M.; Vlcek, J.

    2015-12-01

    The West Bohemia/Vogtland region, central Europe, is a place of localized repeating swarm activity continuously monitored during the last two decades, allowing a detailed study of the driving mechanisms. Previous earthquake episodes where characterized by swarm-type activity with gradual onsets and decays which were not related to mainshocks. However, the latest activity in the year 2014 occurred exactly in the same location as previous swarm activity but consisted of three classical aftershock sequences triggered by a M4.4 event and two ~M3.5 events. The apparent system change from swarm-type to mainshock-aftershock characteristics can have important implications for the understanding of swarm and aftershock generation as well as for seismic hazard assessment in this region. Thus we have analyzed in detail the spatiotemporal aftershock sequence based on a relocated earthquake catalog. Our analysis shows that the largest mainshock occurred in a step-over region of the fault plane with increased Coulomb stress due to previous activity. Its rupture plane connecting both segments is significantly rotated compared to most aftershocks, which occurred in-plane. The aftershock characteristics are classical in the way that (i) the aftershocks are clearly triggered by the mainshock, (ii) the maximum magnitude of the aftershocks is approximately 1.2 units less than the mainshock magnitude (Bath law), and (iii) the decay can be well fitted by the Omori-Utsu law. However, the absolute number of aftershocks and the fitted c and p values of the Omori-Utsu decay are significantly larger than for typical sequences. The fit of the epidemic type aftershock sequence (ETAS) model reveals a time-dependent background activity which exponentially decays with time after the mainshock. Pore pressure simulations with an exponentially decreasing flow rate of the fluid source show a good agreement with the observed spatial migration front of the aftershocks extending approximately with log

  9. The Constantine (Algeria) seismic sequence of 27 October 1985: a new rupture model from aftershock relocation, focal mechanisms, and stress tensors

    NASA Astrophysics Data System (ADS)

    Ousadou, F.; Dorbath, L.; Dorbath, C.; Bounif, M. A.; Benhallou, H.

    2013-04-01

    The October 27, 1985 Constantine earthquake of magnitude MS 5.9 (NEIC) although moderate is the strongest earthquake recorded in the eastern Tellian Atlas (northeast Algeria) since the beginning of instrumental seismology. The main shock locations given by different institutions are scattered and up to 10 km away northwest from the NE-SW 30 km long elongated aftershocks cloud localized by a dedicated temporary portable network. The focal mechanism indicates left-lateral strike-slip on an almost vertical fault with a small reverse component on the northwest dipping plane. This paper presents relocations of the main shock and aftershocks using TomoDD. One hundred thirty-eight individual focal mechanisms have been built allowing the determination of the stress tensor at different scales. A rupture model has been suggested, which explains the different observations of aftershock distribution and stress tensor rotation.

  10. Foreshock and Aftershocks in Simple Earthquake Models

    NASA Astrophysics Data System (ADS)

    Kazemian, J.; Tiampo, K. F.; Klein, W.; Dominguez, R.

    2015-02-01

    Many models of earthquake faults have been introduced that connect Gutenberg-Richter (GR) scaling to triggering processes. However, natural earthquake fault systems are composed of a variety of different geometries and materials and the associated heterogeneity in physical properties can cause a variety of spatial and temporal behaviors. This raises the question of how the triggering process and the structure interact to produce the observed phenomena. Here we present a simple earthquake fault model based on the Olami-Feder-Christensen and Rundle-Jackson-Brown cellular automata models with long-range interactions that incorporates a fixed percentage of stronger sites, or asperity cells, into the lattice. These asperity cells are significantly stronger than the surrounding lattice sites but eventually rupture when the applied stress reaches their higher threshold stress. The introduction of these spatial heterogeneities results in temporal clustering in the model that mimics that seen in natural fault systems along with GR scaling. In addition, we observe sequences of activity that start with a gradually accelerating number of larger events (foreshocks) prior to a main shock that is followed by a tail of decreasing activity (aftershocks). This work provides further evidence that the spatial and temporal patterns observed in natural seismicity are strongly influenced by the underlying physical properties and are not solely the result of a simple cascade mechanism.

  11. Aftershocks in a frictional earthquake model.

    PubMed

    Braun, O M; Tosatti, Erio

    2014-09-01

    Inspired by spring-block models, we elaborate a "minimal" physical model of earthquakes which reproduces two main empirical seismological laws, the Gutenberg-Richter law and the Omori aftershock law. Our point is to demonstrate that the simultaneous incorporation of aging of contacts in the sliding interface and of elasticity of the sliding plates constitutes the minimal ingredients to account for both laws within the same frictional model.

  12. Hypocentral Relocations of the 2008 Mt. Carmel, Illinois Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    Shoemaker, K.; Hamburger, M. W.; Pavlis, G. L.; Horton, S. P.; Withers, M. M.

    2009-12-01

    On April 18, 2008, a moderate sized earthquake (Mw 5.2, hypocentral depth of 16 km) occurred near the Indiana-Illinois state border within 3 km of the Mt. Carmel-New Harmony fault at the northern termination of the Wabash Valley Fault System. A total of 257 aftershocks were recorded over the next month by a fourteen-station temporary network deployed by Indiana University and University of Memphis/Center of Earthquake Research and Information (CERI). The number of recorded aftershocks is greater than aftershocks recorded from previous earthquakes in the WVFS of similar magnitude within the last 50 years. The number and density of local stations allowed the generation of precise hypocentral relocations with the combination of waveform cross-correlation and joint hypocentral techniques. The relocated hypocenters indicate a well-defined near-vertical fault plane striking east-west. The fault orientation is consistent with the focal mechanism of the main shock and nearly orthogonal with respect to the trace of the neighboring Mt. Carmel-New Harmony fault. The interpreted ruptured fault orientation suggests the aftershock sequence occurred on a transfer structure at the fault termination. The structure may be related to the change in deformation styles suggested by the transition from the northeast-trending WVFS to the northwest-trending La Salle anticlinorium.

  13. Discrete characteristics of the aftershock sequence of the 2011 Van earthquake

    NASA Astrophysics Data System (ADS)

    Toker, Mustafa

    2014-10-01

    An intraplate earthquake of magnitude Mw 7.2 occurred on a NE-SW trending blind oblique thrust fault in accretionary orogen, the Van region of Eastern Anatolia on October 23, 2011. The aftershock seismicity in the Van earthquake was not continuous but, rather, highly discrete. This shed light on the chaotic nonuniformity of the event distribution and played key roles in determining the seismic coupling between the rupturing process and seismogeneity. I analyzed the discrete statistical mechanics of the 2011 Van mainshock-aftershock sequence with an estimation of the non-dimensional tuning parameters consisting of; temporal clusters (C) and the random (RN) distribution of aftershocks, range of size scales (ROSS), strength change (εD), temperature (T), P-value of temporal decay, material parameter R-value, seismic coupling χ, and Q-value of aftershock distribution. I also investigated the frequency-size (FS), temporal (T) statistics and the sequential characteristics of aftershock dynamics using discrete approach and examined the discrete evolutionary periods of the Van earthquake Gutenberg-Richter (GR) distribution. My study revealed that the FS and T statistical properties of aftershock sequence represent the Gutenberg-Richter (GR) distribution, clustered (C) in time and random (RN) Poisson distribution, respectively. The overall statistical behavior of the aftershock sequence shows that the Van earthquake originated in a discrete structural framework with high seismic coupling under highly variable faulting conditions. My analyses relate this larger dip-slip event to a discrete seismogenesis with two main components of complex fracturing and branching framework of the ruptured fault and dynamic strengthening and hardening behavior of the earthquake. The results indicate two dynamic cases. The first is associated with aperiodic nature of aftershock distribution, indicating a time-independent Poissonian event. The second is associated with variable slip model

  14. Quantifying the information content of slip models with regard to aftershock forecasting

    NASA Astrophysics Data System (ADS)

    Bach, C.; Hainzl, S.

    2012-12-01

    Coulomb stress changes (ΔCFS) have been recognized as a major trigger mechanism for earthquakes, in particular aftershock distributions and the spatial patterns of ΔCFS are often found to be correlated. However, the Coulomb stress calculations are based on slip inversions and the receiver fault mechanisms which both contain large uncertainties. In particular, slip inversions are usually non-unique and often differ strongly for the same earthquakes. Here we want to address the information content of those inversions with respect to aftershock forecasting. Therefore we compare the slip models to randomized fractal slip models which are only constrained by fault information and moment magnitude. The uncertainty of the aftershock mechanisms is considered by using many receiver fault orientations, and by calculating ΔCFS at several depth layers. The stress change is then converted into an aftershock probability map utilizing a clock advance model. To estimate the information content of the slip models, we use an Epidemic Type Aftershock Sequence (ETAS) model approach introduced by Bach and Hainzl (2012), where the spatial probability density of direct aftershocks is related to the ΔCFS calculations. Besides the directly triggered aftershocks, this approach also takes secondary aftershock triggering into account. We quantify our results by calculating the information gain of the randomized slip models relative to the corresponding published slip model. As case studies, we investigate the aftershock sequences of several well-known main shocks such as 1992 Landers, 1999 Hector Mine, 2002 Denali, 2003 Tokachi-Oki. First results show, that for most of the tested earthquake sequences up to 50% of the random slip models are found to perform better than the originally published model, for some of the tested sequences the information gain is lower than for the published slip model.

  15. No Evidence of Magnitude Clustering in an Aftershock Sequence of Nano- and Picoseismicity

    NASA Astrophysics Data System (ADS)

    Davidsen, Jörn; Kwiatek, Grzegorz; Dresen, Georg

    2012-01-01

    One of the hallmarks of our current understanding of seismicity as highlighted by the epidemic-type-aftershock sequence model is that the magnitudes of earthquakes are independent of one another and can be considered as randomly drawn from the Gutenberg-Richter distribution. This assumption forms the basis of many approaches for forecasting seismicity rates and hazard assessment. Recently, it has been suggested that the assumption of independent magnitudes is not valid. It was subsequently argued that this conclusion was not supported by the original earthquake data from California. One of the main challenges is the lack of completeness of earthquake catalogs. Here, we study an aftershock sequence of nano- and picoseismicity as observed at the Mponeng mine, for which the issue of incompleteness is much less pronounced. We show that this sequence does not exhibit any significant evidence of magnitude correlations.

  16. The relationship between afterslip and aftershocks: a study based on Coulomb-Rate-and-State models

    NASA Astrophysics Data System (ADS)

    Cattania, Camilla; Hainzl, Sebastian; Roth, Frank; Wang, Lifeng

    2014-05-01

    The original Coulomb stress hypothesis, as well as most physics based models of aftershock sequences, assume that aftershocks are triggered by the instantaneous coseismic stress: in other words, the stress field is treated as stationary following the mainshock. However, several lines of evidence indicate that postseismic processes may affect aftershock triggering. The cumulative seismic moment of afterslip can be a significant fraction of the coseismic moment, generating comparable stress changes; moreover, afterslip has a similar time dependence as aftershocks, suggesting that the two processes may be linked. Aftershocks themselves contribute to the redistribution of stresses, and they can trigger their own aftershocks: spatial clustering, and the success of statistical models which include secondary triggering (ETAS) suggest that, even though aftershocks typically generate stresses orders of magnitude smaller than the mainshock, they are significant on a local scale. Our goal is to study the effect of postseismically induced stresses in the spatial and temporal distribution of aftershocks. We focus on the two processes described above (afterslip and secondary triggering), and do not consider other phenomena such as poroelastic response and viscoelastic relaxation. We study a period of 250 days following the mainshock, for two case studies: the Parkfield, Mw=6.0 and the Tohoku, Mw=9.0 earthquakes. We model the seismic response to stress changes using the Dieterich constitutive law, derived from a population of faults governed by Rate-and-State dependent friction; we also consider uncertainties in the input stress field using a Monte Carlo technique. We find that modeling secondary triggering systematically improves model performance; afterslip has a less significant overall impact on the model, but in both cases studies we observe clusters of seismicity which, due to their location relative to the coseismic and postseismic slip, are better explained when afterslip

  17. Aftershocks in coherent-noise models

    NASA Astrophysics Data System (ADS)

    Wilke, C.; Altmeyer, S.; Martinetz, T.

    1998-09-01

    The decay pattern of aftershocks in the so-called ‘coherent-noise’ models [M.E.J. Newman, K. Sneppen, Phys. Rev. E 54 (1996) 6226] is studied in detail. Analytical and numerical results show that the probability to find a large event at time t after an initial major event decreases as t- τ for small t, with the exponent τ ranging from 0 to values well above 1. This is in contrast to Sneppen and Newman, who stated that the exponent is about 1, independent of the microscopic details of the simulation. Numerical simulations of an extended model [C. Wilke, T. Martinetz, Phys. Rev. E 56 (1997) 7128] show that the power-law is only a generic feature of the original dynamics and does not necessarily appear in a more general context. Finally, the implications of the results to the modelling of earthquakes are discussed.

  18. An experimental approach to non - extensive statistical physics and Epidemic Type Aftershock Sequence (ETAS) modeling. The case of triaxially deformed sandstones using acoustic emissions.

    NASA Astrophysics Data System (ADS)

    Stavrianaki, K.; Vallianatos, F.; Sammonds, P. R.; Ross, G. J.

    2014-12-01

    Fracturing is the most prevalent deformation mechanism in rocks deformed in the laboratory under simulated upper crustal conditions. Fracturing produces acoustic emissions (AE) at the laboratory scale and earthquakes on a crustal scale. The AE technique provides a means to analyse microcracking activity inside the rock volume and since experiments can be performed under confining pressure to simulate depth of burial, AE can be used as a proxy for natural processes such as earthquakes. Experimental rock deformation provides us with several ways to investigate time-dependent brittle deformation. Two main types of experiments can be distinguished: (1) "constant strain rate" experiments in which stress varies as a result of deformation, and (2) "creep" experiments in which deformation and deformation rate vary over time as a result of an imposed constant stress. We conducted constant strain rate experiments on air-dried Darley Dale sandstone samples in a variety of confining pressures (30MPa, 50MPa, 80MPa) and in water saturated samples with 20 MPa initial pore fluid pressure. The results from these experiments used to determine the initial loading in the creep experiments. Non-extensive statistical physics approach was applied to the AE data in order to investigate the spatio-temporal pattern of cracks close to failure. A more detailed study was performed for the data from the creep experiments. When axial stress is plotted against time we obtain the trimodal creep curve. Calculation of Tsallis entropic index q is performed to each stage of the curve and the results are compared with the ones from the constant strain rate experiments. The Epidemic Type Aftershock Sequence model (ETAS) is also applied to each stage of the creep curve and the ETAS parameters are calculated. We investigate whether these parameters are constant across all stages of the curve, or whether there are interesting patterns of variation. This research has been co-funded by the European Union

  19. Automatic analysis of the Gorkha earthquake aftershock sequence: evidences of structurally-segmented seismicity

    NASA Astrophysics Data System (ADS)

    Baillard, Christian; Lyon-Caen, Hélène; Bollinger, Laurent; Rietbrock, Andreas; Letort, Jean; Adhikari, Lok Bijaya

    2017-03-01

    We present the first 3 months of aftershock activity following the 25th April 2015 Gorkha earthquake MW 7.8 recorded on the Nepalese Seismic network. We deployed an automatic procedure composed of three main stages: 1) coarse determination of the P and S onsets; 2) phase association to declare events and 3) iterative addition and refinement of onsets using the Kurtosis characteristic function. In total 9188 events could be located in the Kathmandu region with the majority having small location errors (< 4.5, 9, 10 km in the X, Y, Z directions, respectively). Additionally, we propose a new attenuation law to estimate local magnitudes in the region. This new seismic catalog reveals a detailed insight into the Gorkha aftershock sequence and its relation to the main shock rupture models and tectonic structures in the region. Most aftershocks fall within the Main Himalayan Thrust (MHT) shear zone or in its hanging-wall. Significant temporal and lateral variations of aftershocks location are observed among them: 1) three distinct stages, highlighting subsequent jump-offs at the easternmost termination, 2) the existence of a seismic gap north of Kathmandu which matches with a low slip zone in the rupture area of the mainshock, 3) the confinement of seismic activity in the trace of the 12th May MW 7.3 earthquake within the MHT and its hanging-wall through a 30 by 30 km2 region, 4) a shallow westward-dipping structure east of the Kathmandu klippe. These new observations with the inferred tectonic structures at depth suggests a tectonic control of part of the aftershock activity by the lateral breaks along the MHT and by the geometry of the duplex above the thrust.

  20. Recent Experiences in Aftershock Hazard Modelling in New Zealand

    NASA Astrophysics Data System (ADS)

    Gerstenberger, M.; Rhoades, D. A.; McVerry, G.; Christophersen, A.; Bannister, S. C.; Fry, B.; Potter, S.

    2014-12-01

    The occurrence of several sequences of earthquakes in New Zealand in the last few years has meant that GNS Science has gained significant recent experience in aftershock hazard and forecasting. First was the Canterbury sequence of events which began in 2010 and included the destructive Christchurch earthquake of February, 2011. This sequence is occurring in what was a moderate-to-low hazard region of the National Seismic Hazard Model (NSHM): the model on which the building design standards are based. With the expectation that the sequence would produce a 50-year hazard estimate in exceedance of the existing building standard, we developed a time-dependent model that combined short-term (STEP & ETAS) and longer-term (EEPAS) clustering with time-independent models. This forecast was combined with the NSHM to produce a forecast of the hazard for the next 50 years. This has been used to revise building design standards for the region and has contributed to planning of the rebuilding of Christchurch in multiple aspects. An important contribution to this model comes from the inclusion of EEPAS, which allows for clustering on the scale of decades. EEPAS is based on three empirical regressions that relate the magnitudes, times of occurrence, and locations of major earthquakes to regional precursory scale increases in the magnitude and rate of occurrence of minor earthquakes. A second important contribution comes from the long-term rate to which seismicity is expected to return in 50-years. With little seismicity in the region in historical times, a controlling factor in the rate is whether-or-not it is based on a declustered catalog. This epistemic uncertainty in the model was allowed for by using forecasts from both declustered and non-declustered catalogs. With two additional moderate sequences in the capital region of New Zealand in the last year, we have continued to refine our forecasting techniques, including the use of potential scenarios based on the aftershock

  1. Long aftershock sequences within continents and implications for earthquake hazard assessment.

    PubMed

    Stein, Seth; Liu, Mian

    2009-11-05

    One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere.

  2. The Mw=8.8 Maule earthquake aftershock sequence, event catalog and locations

    NASA Astrophysics Data System (ADS)

    Meltzer, A.; Benz, H.; Brown, L.; Russo, R. M.; Beck, S. L.; Roecker, S. W.

    2011-12-01

    The aftershock sequence of the Mw=8.8 Maule earthquake off the coast of Chile in February 2010 is one of the most well-recorded aftershock sequences from a great megathrust earthquake. Immediately following the Maule earthquake, teams of geophysicists from Chile, France, Germany, Great Britain and the United States coordinated resources to capture aftershocks and other seismic signals associated with this significant earthquake. In total, 91 broadband, 48 short period, and 25 accelerometers stations were deployed above the rupture zone of the main shock from 33-38.5°S and from the coast to the Andean range front. In order to integrate these data into a unified catalog, the USGS National Earthquake Information Center develop procedures to use their real-time seismic monitoring system (Bulletin Hydra) to detect, associate, location and compute earthquake source parameters from these stations. As a first step in the process, the USGS has built a seismic catalog of all M3.5 or larger earthquakes for the time period of the main aftershock deployment from March 2010-October 2010. The catalog includes earthquake locations, magnitudes (Ml, Mb, Mb_BB, Ms, Ms_BB, Ms_VX, Mc), associated phase readings and regional moment tensor solutions for most of the M4 or larger events. Also included in the catalog are teleseismic phases and amplitude measures and body-wave MT and CMT solutions for the larger events, typically M5.5 and larger. Tuning of automated detection and association parameters should allow a complete catalog of events to approximately M2.5 or larger for that dataset of more than 164 stations. We characterize the aftershock sequence in terms of magnitude, frequency, and location over time. Using the catalog locations and travel times as a starting point we use double difference techniques to investigate relative locations and earthquake clustering. In addition, phase data from candidate ground truth events and modeling of surface waves can be used to calibrate the

  3. A New Hybrid STEP/Coulomb model for Aftershock Forecasting

    NASA Astrophysics Data System (ADS)

    Steacy, S.; Jimenez, A.; Gerstenberger, M.

    2014-12-01

    Aftershock forecasting models tend to fall into two classes - purely statistical approaches based on clustering, b-value, and the Omori-Utsu law; and Coulomb rate-state models which relate the forecast increase in rate to the magnitude of the Coulomb stress change. Recently, hybrid models combining physical and statistical forecasts have begun to be developed, for example by Bach and Hainzl (2012) and Steacy et al. (2013). The latter approach combined Coulomb stress patterns with the STEP (short-term earthquake probability) model by redistributing expected rate from areas with decreased stress to regions where the stress had increased. The chosen 'Coulomb Redistribution Parameter' (CRP) was 0.93, based on California earthquakes, which meant that 93% of the total rate was expected to occur where the stress had increased. The model was tested against the Canterbury sequence and the main result was that the new model performed at least as well as, and often better than, STEP when tested against retrospective data but that STEP was generally better in pseudo-prospective tests that involved data actually available within the first 10 days of each event of interest. The authors suggested that the major reason for this discrepancy was uncertainty in the slip models and, particularly, in the geometries of the faults involved in each complex major event. Here we develop a variant of the STEP/Coulomb model in which the CRP varies based on the percentage of aftershocks that occur in the positively stressed areas during the forecast learning period. We find that this variant significantly outperforms both STEP and the previous hybrid model in almost all cases, even when the input Coulomb model is quite poor. Our results suggest that this approach might be more useful than Coulomb rate-state when the underlying slip model is not well constrained due to the dependence of that method on the magnitude of the Coulomb stress change.

  4. An Improved Source-Scanning Algorithm for Locating Earthquake Clusters or Aftershock Sequences

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Kao, H.; Hsu, S.

    2010-12-01

    The Source-scanning Algorithm (SSA) was originally introduced in 2004 to locate non-volcanic tremors. Its application was later expanded to the identification of earthquake rupture planes and the near-real-time detection and monitoring of landslides and mud/debris flows. In this study, we further improve SSA for the purpose of locating earthquake clusters or aftershock sequences when only a limited number of waveform observations are available. The main improvements include the application of a ground motion analyzer to separate P and S waves, the automatic determination of resolution based on the grid size and time step of the scanning process, and a modified brightness function to utilize constraints from multiple phases. Specifically, the improved SSA (named as ISSA) addresses two major issues related to locating earthquake clusters/aftershocks. The first one is the massive amount of both time and labour to locate a large number of seismic events manually. And the second one is to efficiently and correctly identify the same phase across the entire recording array when multiple events occur closely in time and space. To test the robustness of ISSA, we generate synthetic waveforms consisting of 3 separated events such that individual P and S phases arrive at different stations in different order, thus making correct phase picking nearly impossible. Using these very complicated waveforms as the input, the ISSA scans all model space for possible combination of time and location for the existence of seismic sources. The scanning results successfully associate various phases from each event at all stations, and correctly recover the input. To further demonstrate the advantage of ISSA, we apply it to the waveform data collected by a temporary OBS array for the aftershock sequence of an offshore earthquake southwest of Taiwan. The overall signal-to-noise ratio is inadequate for locating small events; and the precise arrival times of P and S phases are difficult to

  5. Triggering of tsunamigenic aftershocks from large strike-slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence

    NASA Astrophysics Data System (ADS)

    Geist, Eric L.; Parsons, Tom

    2005-10-01

    The November 2000 New Ireland earthquake sequence started with a Mw = 8.0 left-lateral main shock on 16 November and was followed by a series of aftershocks with primarily thrust mechanisms. The earthquake sequence was associated with a locally damaging tsunami on the islands of New Ireland and nearby New Britain, Bougainville, and Buka. Results from numerical tsunami-propagation models of the main shock and two of the largest thrust aftershocks (Mw > 7.0) indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock, off the southern tip of New Ireland (Aftershock 1). Numerical modeling and tide gauge records at regional and far-field distances indicate that the main shock also generated tsunami waves. Large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event. Most of the damage on Bougainville and Buka Islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands. Modeling of changes in the Coulomb failure stress field caused by the main shock indicate that Aftershock 1 was likely triggered by static stress changes, provided the fault was on or synthetic to the New Britain interplate thrust as specified by the Harvard CMT mechanism. For other possible focal mechanisms of Aftershock 1 and the regional occurrence of thrust aftershocks in general, evidence for static stress change triggering is not as clear. Other triggering mechanisms such as changes in dynamic stress may also have been important. The 2000 New Ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike-slip earthquakes. Similar tectonic regimes that include offshore accommodation structures near large strike-slip faults are found in southern California, the Sea of Marmara, Turkey, along the Queen Charlotte fault in British Columbia

  6. Aftershock seismicity of the 2010 Maule Mw=8.8 Chile, earthquake: Correlation between co-seismic slip models and aftershock distribution?

    USGS Publications Warehouse

    Rietbrock, A.; Ryder, I.; Hayes, G.; Haberland, C.; Comte, D.; Roecker, S.

    2012-01-01

    The 27 February 2010 Maule, Chile (Mw=8.8) earthquake is one of the best instrumentally observed subduction zone megathrust events. Here we present locations, magnitudes and cumulative equivalent moment of the first -2 months of aftershocks, recorded on a temporary network deployed within 2 weeks of the occurrence of the mainshock. Using automatically-determined onset times and a back projection approach for event association, we are able to detect over 30,000 events in the time period analyzed. To further increase the location accuracy, we systematically searched for potential S-wave arrivals and events were located in a regional 2D velocity model. Additionally, we calculated regional moment tensors to gain insight into the deformation history of the aftershock sequence. We find that the aftershock seismicity is concentrated between 40 and 140 km distance from the trench over a depth range of 10 to 35 km. Focal mechanisms indicate a predominance of thrust faulting, with occasional normal faulting events. Increased activity is seen in the outer-rise region of the Nazca plate, predominantly in the northern part of the rupture area. Further down-dip, a second band of clustered seismicity, showing mainly thrust motion, is located at depths of 40–45 km. By comparing recent published mainshock source inversions with our aftershock distribution, we discriminate slip models based on the assumption that aftershocks occur in areas of rapid transition between high and low slip, surrounding high-slip regions of the mainshock.

  7. Integrated Seismicity Model to Detect Pairs of Possible Interdependent Earthquakes and Its Application to Aftershocks of the 2011 Tohoku-Oki Earthquake and Sequence of the 2014 Kermadec and Rat Islands Earthquakes

    NASA Astrophysics Data System (ADS)

    Miyazawa, M.; Tamura, R.

    2015-12-01

    We introduce an integrated seismicity model to stochastically evaluate the time intervals of consecutive earthquakes at global scales, making it possible to detect a pair of earthquakes that are remotely located and possibly related to each other. The model includes seismicity in non-overlapping areas and comprehensively explains the seismicity on the basis of point process models, which include the stationary Poisson model, the aftershock decay model following Omori-Utsu's law, and/or the epidemic-type aftershock sequence (ETAS) model. By use of this model, we examine the possibility of remote triggering of the 2011 M6.4 eastern Shizuoka earthquake in the vicinity of Mt. Fuji that occurred 4 days after the Mw9.0 Tohoku-Oki earthquake and 4 minutes after the M6.2 off-Fukushima earthquake that located about 400 km away, and that of the 2014 Mw7.9 Rat Islands earthquake that occurred within one hour after the Mw6.7 Kermadec earthquake that located about 9,000 km away and followed two large (Mw6.9, 6.5) earthquakes in the region. Both target earthquakes occurred during the passage of surface waves propagating from the previous large events. We estimated probability that the time interval is shorter than that between consecutive events and obtained dynamic stress changes on the faults. The results indicate that the M6.4 eastern Shizuoka event may be rather triggered by the static stress changes from the Tohoku-Oki earthquake and that the Mw7.9 Rat Islands event may have been remotely triggered by the Kermadec events possibly via cyclic fatigue.

  8. Modelling aftershock migration and afterslip of the San Juan Bautista, California, earthquake of October 3, 1972

    USGS Publications Warehouse

    Wesson, R.L.

    1987-01-01

    The San Juan Bautista earthquake of October 3, 1972 (ML = 4.8), located along the San Andreas fault in central California, initiated an aftershock sequence characterized by a subtle, but perceptible, tendency for aftershocks to spread to the northwest and southeast along the fault zone. The apparent dimension of the aftershock zone along strike increased from about 7-10 km within a few days of the earthquake, to about 20 km eight months later. In addition, the mainshock initiated a period of accelerated fault creep, which was observed at 2 creep meters situated astride the trace of the San Andreas fault within about 15 km of the epicenter of the mainshock. The creep rate gradually returned to the preearthquake rate after about 3 yrs. Both the spreading of the aftershocks and the rapid surface creep are interpreted as reflecting a period of rapid creep in the fault zone representing the readjustment of stress and displacement following the failure of a "stuck" patch or asperity during the San Juan Bautista earthquake. Numerical calculations suggest that the behavior of the fault zone is consistent with that of a material characterized by a viscosity of about 3.6??1014 P, although the real rheology is likely to be more complicated. In this model, the mainshock represents the failure of an asperity that slips only during earthquakes. Aftershocks represent the failure of second-order asperities which are dragged along by the creeping fault zone. ?? 1987.

  9. The Hellenic Seismological Network Of Crete (HSNC): Validation and results of the 2013 aftershock sequences

    NASA Astrophysics Data System (ADS)

    Chatzopoulos, Georgios; Papadopoulos, Ilias; Vallianatos, Filippos

    2015-04-01

    The number and quality of seismological networks in Europe has increased in the past decades. Nevertheless, the need for localized networks monitoring areas of great seismic and scientific interest is constant. Hellenic Seismological Network of Crete (HSNC) covers this need for the vicinity of the South Aegean Sea and Crete Island. In the present work with the use of Z-map software (www.seismo.ethz.ch) the spatial variability of Magnitude of Completeness (Mc) is calculated from HSNC's manual analysis catalogue of events for the period 2011 until today, proving the good coverage of HSNC in the areas. Furthermore the 2013, South Aegean seismicity where two large shallow earthquakes occurred in the vicinity of Crete Island, is discussed. The first event takes place on 15th June 2013 in the front of the Hellenic Arc, south from central Crete, while the second one on 12th October, 2013 on the western part of Crete. The two main shocks and their aftershock sequences have been relocated with the use of hypoinverse earthquake location software and an appropriate crust model. The HSNC identified more than 500 and 300 aftershocks respectively followed after the main events. The detailed construction of aftershocks catalogue permits the applicability of modern theories based on complexity sciences as described recently in the frame of non extensive statistical physics. In addition site effects in the stations locations are presented using event and noise recordings. This work was implemented through the project IMPACT-ARC in the framework of action "ARCHIMEDES III-Support of Research Teams at TEI of Crete" (MIS380353) of the Operational Program "Education and Lifelong Learning" and is co-financed by the European Union (European Social Fund) and Greek national funds References A. Tzanis and F. Vallianatos, "Distributed power-law seismicity changes and crustal deformation in the EW Hellenic Arc", Natural Hazards and Earth Systems Sciences, 3, 179-195, 2003 F. Vallianatos, G

  10. Three Ingredients for Improved Global Aftershock Forecasts: Tectonic Region, Time-Dependent Catalog Incompleteness, and Inter-Sequence Variability

    NASA Astrophysics Data System (ADS)

    Page, M. T.; Hardebeck, J.; Felzer, K. R.; Michael, A. J.; van der Elst, N.

    2015-12-01

    Following a large earthquake, seismic hazard can be orders of magnitude higher than the long-term average as a result of aftershock triggering. Due to this heightened hazard, there is a demand from emergency managers and the public for rapid, authoritative, and reliable aftershock forecasts. In the past, USGS aftershock forecasts following large, global earthquakes have been released on an ad-hoc basis with inconsistent methods, and in some cases, aftershock parameters adapted from California. To remedy this, we are currently developing an automated aftershock product that will generate more accurate forecasts based on the Reasenberg and Jones (Science, 1989) method. To better capture spatial variations in aftershock productivity and decay, we estimate regional aftershock parameters for sequences within the Garcia et al. (BSSA, 2012) tectonic regions. We find that regional variations for mean aftershock productivity exceed a factor of 10. The Reasenberg and Jones method combines modified-Omori aftershock decay, Utsu productivity scaling, and the Gutenberg-Richter magnitude distribution. We additionally account for a time-dependent magnitude of completeness following large events in the catalog. We generalize the Helmstetter et al. (2005) equation for short-term aftershock incompleteness and solve for incompleteness levels in the global NEIC catalog following large mainshocks. In addition to estimating average sequence parameters within regions, we quantify the inter-sequence parameter variability. This allows for a more complete quantification of the forecast uncertainties and Bayesian updating of the forecast as sequence-specific information becomes available.

  11. Properties of foreshocks and aftershocks of the nonconservative self-organized critical Olami-Feder-Christensen model.

    PubMed

    Helmstetter, Agnès; Hergarten, Stefan; Sornette, Didier

    2004-10-01

    Following Phys. Rev. Lett. 88, 238501 (2002)] who discovered aftershocks and foreshocks in the Olami-Feder-Christensen (OFC) discrete block-spring earthquake model, we investigate to what degree the simple toppling mechanism of this model is sufficient to account for the clustering of real seismicity in time and space. We find that synthetic catalogs generated by the OFC model share many properties of real seismicity at a qualitative level: Omori's law (aftershocks) and inverse Omori's law (foreshocks), increase of the number of aftershocks and of the aftershock zone size with the mainshock magnitude. There are, however, significant quantitative differences. The number of aftershocks per mainshock in the OFC model is smaller than in real seismicity, especially for large mainshocks. We find that foreshocks in the OFC catalogs can be in large part described by a simple model of triggered seismicity, such as the epidemic-type aftershock sequence (ETAS) model. But the properties of foreshocks in the OFC model depend on the mainshock magnitude, in qualitative agreement with the critical earthquake model and in disagreement with real seismicity and with the ETAS model.

  12. Properties of foreshocks and aftershocks of the nonconservative self-organized critical Olami-Feder-Christensen model

    SciTech Connect

    Helmstetter, Agnes; Hergarten, Stefan; Sornette, Didier

    2004-10-01

    Following Hergarten and Neugebauer [Phys. Rev. Lett. 88, 238501, 2002] who discovered aftershocks and foreshocks in the Olami-Feder-Christensen (OFC) discrete block-spring earthquake model, we investigate to what degree the simple toppling mechanism of this model is sufficient to account for the clustering of real seismicity in time and space. We find that synthetic catalogs generated by the OFC model share many properties of real seismicity at a qualitative level: Omori's law (aftershocks) and inverse Omori's law (foreshocks), increase of the number of aftershocks and of the aftershock zone size with the mainshock magnitude. There are, however, significant quantitative differences. The number of aftershocks per mainshock in the OFC model is smaller than in real seismicity, especially for large mainshocks. We find that foreshocks in the OFC catalogs can be in large part described by a simple model of triggered seismicity, such as the epidemic-type aftershock sequence (ETAS) model. But the properties of foreshocks in the OFC model depend on the mainshock magnitude, in qualitative agreement with the critical earthquake model and in disagreement with real seismicity and with the ETAS model.

  13. Scaling Analysis of Time Distribution between Successive Earthquakes in Aftershock Sequences

    NASA Astrophysics Data System (ADS)

    Marekova, Elisaveta

    2016-08-01

    The earthquake inter-event time distribution is studied, using catalogs for different recent aftershock sequences. For aftershock sequences following the Modified Omori's Formula (MOF) it seems clear that the inter-event distribution is a power law. The parameters of this law are defined and they prove to be higher than the calculated value (2-1/ p). Based on the analysis of the catalogs, it is determined that the probability densities of the inter-event time distribution collapse into a single master curve when the data is rescaled with instantaneous intensity, R( t; M th ), defined by MOF. The curve is approximated by a gamma distribution. The collapse of the data provides a clear view of aftershock-occurrence self-similarity.

  14. Generalized Omori-Utsu law for aftershock sequences in southern California

    NASA Astrophysics Data System (ADS)

    Davidsen, J.; Gu, C.; Baiesi, M.

    2015-05-01

    We investigate the validity of a proposed generalized Omori-Utsu law for the aftershock sequences for the Landers, Hector Mine, Northridge and Superstition Hills earthquakes, the four largest events in the southern California catalogue we analyse. This law unifies three of the most prominent empirical laws of statistical seismology-the Gutenberg-Richter law, the Omori-Utsu law, and a generalized version of Båth's law-in a formula casting the parameters in the Omori-Utsu law as a function of the lower magnitude cutoff mc for the aftershocks considered. By applying a recently established general procedure for identifying aftershocks, we confirm that the generalized Omori-Utsu law provides a good approximation for the observed rates overall. In particular, we provide convincing evidence that the characteristic time c is not constant but a genuine function of mc, which cannot be attributed to short-term aftershock incompleteness. However, the estimation of the specific parameters is somewhat sensitive to the aftershock selection method used. This includes c(mc), which has important implications for inferring the underlying stress field.

  15. The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks

    NASA Astrophysics Data System (ADS)

    Brandsdottir, B.; Parsons, M.; White, R. S.; Gudmundsson, O.; Drew, J.

    2010-12-01

    The mid-Atlantic plate boundary breaks up into a series of segments across Iceland. The South Iceland Seismic Zone (SISZ) is a complex transform zone where left-lateral E-W shear between the Reykjanes Peninsula Rift Zone and the Eastern Volcanic Zone is accommodated by bookshelf faulting along N-S lateral strike-slip faults. The SISZ is also a transient feature, migrating sideways in response to the southward propagation of the Eastern Volcanic Zone. Sequences of large earthquakes (M > 6) lasting from days to years and affecting most of the seismic zone have occurred repeatedly in historical time (last 1100 years), separated by intervals of relative quiescence lasting decades to more than a century. On May 29 2008, a Mw 6.1 earthquake struck the western part of the South Iceland Seismic Zone, followed within seconds by a slightly smaller event on a second fault ~5 km further west. Aftershocks, detected by a temporal array of 11 seismometers and three permanent Icelandic Meteorological Office stations were located using an automated Coalescence Microseismic Mapping technique. The epicenters delineate two major and several smaller N-S faults as well as an E-W zone of activity stretching further west into the Reykjanes Peninsula Rift Zone. Fault plane solutions show both right lateral and oblique strike slip mechanisms along the two major N-S faults. The aftershocks deepen from 3-5 km in the north to 8-9 km in the south, suggesting that the main faults dip southwards. The faulting is interpreted to be driven by the local stress due to transform motion between two parallel segments of the divergent plate boundary crossing Iceland.

  16. Spatial Variations of Aftershock Parameters and their Relation to Geodetic Slip Models for the 2010 Mw8.8 Maule and the 2011 Mw9.0 Tohoku-oki Earthquakes

    NASA Astrophysics Data System (ADS)

    Zakharova, O.; Hainzl, S.; Lange, D.; Enescu, B.

    2017-01-01

    Recent development in analysis tools and deployments of the geodetic and seismic instruments give an opportunity to investigate aftershock sequences at local scales, which is important for the seismic hazard assessment. In particular, we study the dependencies between aftershock sequences properties and deformational/geological data on a scale of the rupture extension of megathrust earthquakes. For this goal we use, on one hand, published models of inter-, co- and postseismic slip and geological information and, on the other hand, aftershock parameters, obtained by fitting a modified Epidemic Type Aftershock Sequence (ETAS) model. The altered ETAS model takes into account the mainshock rupture extension and it distinguishes between primary and the secondary aftershock triggering involved in the total seismicity rate. We estimate the Spearman correlation coefficients between the spatially distributed aftershock parameters estimated by the modified ETAS model and crustal physical properties for the Maule 2010 Mw8.8 and the Tohoku-oki 2011 Mw9.0 aftershock sequences. We find that: (1) modified ETAS model outperforms the classical one, when the mainshock rupture extension cannot be neglected and represented as a point source; (2) anomalous aftershock parameters occur in the areas of the reactivated fault systems; (3) aftershocks, regardless of their generation, tend to occur in the areas of high coseismic slip gradient, afterslip and interseismic coupling; (4) aftershock seismic moment releases preferentially in regions of large coseismic slip, coseismic slip gradient and interseismically locked areas; (5) b value tends to be smaller in interseismically locked regions.

  17. On the relationship between lower magnitude thresholds and bias in epidemic-type aftershock sequence parameter estimates

    NASA Astrophysics Data System (ADS)

    Schoenberg, Frederic Paik; Chu, Annie; Veen, Alejandro

    2010-04-01

    Modern earthquake catalogs are often described using spatial-temporal point process models such as the epidemic-type aftershock sequence (ETAS) models of Ogata (1998). Earthquake catalogs often have issues of incompleteness and other inaccuracies for earthquakes of magnitude below a certain threshold, and such earthquakes are typically removed prior to fitting a point process model. This paper investigates the bias in the parameters in ETAS models introduced by the removal of the smallest events. It is shown that in the case of most of the ETAS parameters, the bias increases approximately exponentially as a function of the lower magnitude cutoff.

  18. Diffusion of epicenters of earthquake aftershocks, Omori's law, and generalized continuous-time random walk models.

    PubMed

    Helmstetter, A; Sornette, D

    2002-12-01

    The epidemic-type aftershock sequence (ETAS) model is a simple stochastic process modeling seismicity, based on the two best-established empirical laws, the Omori law (power-law decay approximately 1/t(1+theta) of seismicity after an earthquake) and Gutenberg-Richter law (power-law distribution of earthquake energies). In order to describe also the space distribution of seismicity, we use in addition a power-law distribution approximately 1/r(1+mu) of distances between triggered and triggering earthquakes. The ETAS model has been studied for the last two decades to model real seismicity catalogs and to obtain short-term probabilistic forecasts. Here, we present a mapping between the ETAS model and a class of CTRW (continuous time random walk) models, based on the identification of their corresponding master equations. This mapping allows us to use the wealth of results previously obtained on anomalous diffusion of CTRW. After translating into the relevant variable for the ETAS model, we provide a classification of the different regimes of diffusion of seismic activity triggered by a mainshock. Specifically, we derive the relation between the average distance between aftershocks and the mainshock as a function of the time from the mainshock and of the joint probability distribution of the times and locations of the aftershocks. The different regimes are fully characterized by the two exponents theta and mu. Our predictions are checked by careful numerical simulations. We stress the distinction between the "bare" Omori law describing the seismic rate activated directly by a mainshock and the "renormalized" Omori law taking into account all possible cascades from mainshocks to aftershocks of aftershock of aftershock, and so on. In particular, we predict that seismic diffusion or subdiffusion occurs and should be observable only when the observed Omori exponent is less than 1, because this signals the operation of the renormalization of the bare Omori law, also at the

  19. Three ingredients for Improved global aftershock forecasts: Tectonic region, time-dependent catalog incompleteness, and inter-sequence variability

    USGS Publications Warehouse

    Page, Morgan T.; Van Der Elst, Nicholas; Hardebeck, Jeanne L.; Felzer, Karen; Michael, Andrew J.

    2016-01-01

    Following a large earthquake, seismic hazard can be orders of magnitude higher than the long‐term average as a result of aftershock triggering. Because of this heightened hazard, emergency managers and the public demand rapid, authoritative, and reliable aftershock forecasts. In the past, U.S. Geological Survey (USGS) aftershock forecasts following large global earthquakes have been released on an ad hoc basis with inconsistent methods, and in some cases aftershock parameters adapted from California. To remedy this, the USGS is currently developing an automated aftershock product based on the Reasenberg and Jones (1989) method that will generate more accurate forecasts. To better capture spatial variations in aftershock productivity and decay, we estimate regional aftershock parameters for sequences within the García et al. (2012) tectonic regions. We find that regional variations for mean aftershock productivity reach almost a factor of 10. We also develop a method to account for the time‐dependent magnitude of completeness following large events in the catalog. In addition to estimating average sequence parameters within regions, we develop an inverse method to estimate the intersequence parameter variability. This allows for a more complete quantification of the forecast uncertainties and Bayesian updating of the forecast as sequence‐specific information becomes available.

  20. The aftershock sequence of the 2015 April 25 Gorkha-Nepal earthquake

    NASA Astrophysics Data System (ADS)

    Adhikari, L. B.; Gautam, U. P.; Koirala, B. P.; Bhattarai, M.; Kandel, T.; Gupta, R. M.; Timsina, C.; Maharjan, N.; Maharjan, K.; Dahal, T.; Hoste-Colomer, R.; Cano, Y.; Dandine, M.; Guilhem, A.; Merrer, S.; Roudil, P.; Bollinger, L.

    2015-12-01

    The M 7.8 2015 April 25 Gorkha earthquake devastated the mountainous southern rim of the High Himalayan range in central Nepal. The main shock was followed by 553 earthquakes of local magnitude greater than 4.0 within the first 45 days. In this study, we present and qualify the bulletin of the permanent National Seismological Centre network to determine the spatio-temporal distribution of the aftershocks. The Gorkha sequence defines a ˜140-km-long ESE trending structure, parallel to the mountain range, abutting on the presumed extension of the rupture plane of the 1934 M 8.4 earthquake. In addition, we observe a second seismicity belt located southward, under the Kathmandu basin and in the northern part of the Mahabarat range. Many aftershocks of the Gorkha earthquake sequence have been felt by the 3 millions inhabitants of the Kathmandu valley.

  1. Short-term forecasting of aftershock sequences, microseismicity and swarms inside the Corinth Gulf continental rift

    NASA Astrophysics Data System (ADS)

    Segou, Margarita

    2014-05-01

    Corinth Gulf (Central Greece) is the fastest continental rift in the world with extension rates 11-15 mm/yr with diverse seismic deformation including earthquakes with M greater than 6.0, several periods of increased microseismic activity, usually lasting few months and possibly related with fluid diffusion, and swarm episodes lasting few days. In this study I perform a retrospective forecast experiment between 1995-2012, focusing on the comparison between physics-based and statistical models for short term time classes. Even though Corinth gulf has been studied extensively in the past there is still today a debate whether earthquake activity is related with the existence of either a shallow dipping structure or steeply dipping normal faults. In the light of the above statement, two CRS realization are based on resolving Coulomb stress changes on specified receiver faults, expressing the aforementioned structural models, whereas the third CRS model uses optimally-oriented for failure planes. The CRS implementation accounts for stress changes following all major ruptures with M greater than 4.5 within the testing phase. I also estimate fault constitutive parameters from modeling the response to major earthquakes at the vicinity of the gulf (Aσ=0.2, stressing rate app. 0.02 bar/yr). The generic ETAS parameters are taken as the maximum likelihood estimates derived from the stochastic declustering of the modern seismicity catalog (1995-2012) with minimum triggering magnitude M2.5. I test whether the generic ETAS can efficiently describe the aftershock spatio-temporal clustering but also the evolution of swarm episodes and microseismicity. For the reason above, I implement likelihood tests to evaluate the forecasts for their spatial consistency and for the total amount of predicted versus observed events with M greater than 3.0 in 10-day time windows during three distinct evaluation phases; the first evaluation phase focuses on the Aigio 1995 aftershock sequence (15

  2. The Mw 5.8 Mineral, Virginia, earthquake of August 2011 and aftershock sequence: constraints on earthquake source parameters and fault geometry

    USGS Publications Warehouse

    McNamara, Daniel E.; Benz, H.M.; Herrmann, Robert B.; Bergman, Eric A.; Earle, Paul; Meltzer, Anne; Withers, Mitch; Chapman, Martin

    2014-01-01

    The Mw 5.8 earthquake of 23 August 2011 (17:51:04 UTC) (moment, M0 5.7×1017  N·m) occurred near Mineral, Virginia, within the central Virginia seismic zone and was felt by more people than any other earthquake in United States history. The U.S. Geological Survey (USGS) received 148,638 felt reports from 31 states and 4 Canadian provinces. The USGS PAGER system estimates as many as 120,000 people were exposed to shaking intensity levels of IV and greater, with approximately 10,000 exposed to shaking as high as intensity VIII. Both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast‐striking reverse fault that nucleated at a depth of approximately 7±2  km. The distribution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western United States (Horton and Williams, 2012). Near‐source and far‐field damage reports, which extend as far away as Washington, D.C., (135 km away) and Baltimore, Maryland, (200 km away) are consistent with an earthquake of this size and depth in the eastern United States (EUS). Within the first few days following the earthquake, several government and academic institutions installed 36 portable seismograph stations in the epicentral region, making this among the best‐recorded aftershock sequences in the EUS. Based on modeling of these data, we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry, area of rupture, and observations of the aftershock sequence magnitude–frequency and temporal distribution. The observed slope of the magnitude–frequency curve or b‐value for the aftershock sequence is consistent with previous EUS studies (b=0.75), suggesting that most of the accumulated strain was released by the mainshock. The aftershocks define a rupture that extends between approximately 2–8 km in depth and 8–10 km along

  3. Operational Earthquake Forecasting of Aftershocks for New England

    NASA Astrophysics Data System (ADS)

    Ebel, J.; Fadugba, O. I.

    2015-12-01

    Although the forecasting of mainshocks is not possible, recent research demonstrates that probabilistic forecasts of expected aftershock activity following moderate and strong earthquakes is possible. Previous work has shown that aftershock sequences in intraplate regions behave similarly to those in California, and thus the operational aftershocks forecasting methods that are currently employed in California can be adopted for use in areas of the eastern U.S. such as New England. In our application, immediately after a felt earthquake in New England, a forecast of expected aftershock activity for the next 7 days will be generated based on a generic aftershock activity model. Approximately 24 hours after the mainshock, the parameters of the aftershock model will be updated using the observed aftershock activity observed to that point in time, and a new forecast of expected aftershock activity for the next 7 days will be issued. The forecast will estimate the average number of weak, felt aftershocks and the average expected number of aftershocks based on the aftershock statistics of past New England earthquakes. The forecast also will estimate the probability that an earthquake that is stronger than the mainshock will take place during the next 7 days. The aftershock forecast will specify the expected aftershocks locations as well as the areas over which aftershocks of different magnitudes could be felt. The system will use web pages, email and text messages to distribute the aftershock forecasts. For protracted aftershock sequences, new forecasts will be issued on a regular basis, such as weekly. Initially, the distribution system of the aftershock forecasts will be limited, but later it will be expanded as experience with and confidence in the system grows.

  4. Adaptive forecasting of aftershock activity after the main shock

    NASA Astrophysics Data System (ADS)

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2014-05-01

    Forecasting aftershock activity is useful to reduce seismic risks in the affected area after the main shock. The difficulties to forecast aftershocks are (i) a forecasting model should be tailored to each aftershock sequence because the statistical property varies greatly according to an individual aftershock sequence and (ii) the forecasting model has to be estimated from highly deficient data where a significant fraction of early small aftershocks are missing from seismic records. To overcome this difficulty, we have been developing a statistical model to deal with incompletely detected aftershocks, in which the detection rate of aftershocks is sequentially estimated in a state-space modeling approach. Our method enables us to robustly estimate the forecasting model of underlying aftershocks including not only observed aftershocks but also missing ones from the incomplete catalog. We show that the Omori-Utsu formula can be well estimated only from a few hours of the data, and then it can be revised by the epidemic type aftershock sequence (ETAS) model to adaptively forecast an aftershock sequence with the individual cascading feature as the data size increases in real-time. We demonstrate that how these estimated models can effectively forecast the aftershock activity. We also discuss how these models can be implemented in an operational system for earthquake forecasting. References: T. Omi, Y. Ogata, Y. Hirata, and K. Aihiara, "Forecasting large aftershocks within one day after the main shock", Scientific Reports, 3, 2218 (2013). T. Omi, Y. Ogata, Y. Hirata, and K. Aihiara, "Estimating the ETAS model from an early aftershock sequence", (In submission).

  5. Hurricane Irene's Impacts on the Aftershock Sequence of the 2011 Mw5.8 Virginia Earthquake

    NASA Astrophysics Data System (ADS)

    Meng, X.; Peng, Z.; Yang, H.; Allman, S.

    2013-12-01

    Recent studies have shown that typhoon could trigger shallow slow-slip events in Taiwan. However, it is unclear whether such extreme weather events could affect the occurrence of regular earthquakes as well. A good opportunity to test this hypothesis occurred in 2011 when an Mw 5.8 earthquake struck Louisa County, Virginia. This event ruptured a shallow, reverse fault. Roughly 5 days later, hurricane Irene struck the coast of Norfolk, Virginia, which is near the epicentral region of the Virginia mainshock. Because aftershocks listed in the ANSS catalog were incomplete immediately after the main shock, it is very difficult to find the genuine correlation between the seismicity rate changes and hurricane Irene. Hence, we use a recently developed waveform matched filter technique to scan through the continuous seismic data to detect small aftershocks that are previously unidentified. A mixture of 7 temporary stations from the IRIS Ramp deployment and 8 temporary stations deployed by Virginia Tech is used. The temporary stations were set up between 24 to 72 hours following the main shock around its immediate vicinity, which provides us a unique dataset recording the majority aftershock sequence of an intraplate earthquake. We us 80 aftershocks identified by Chapman [2013] as template events and scan through the continuous data from 23 August 2011 through 10 September 2011. So far, we have detected 704 events using a threshold of 12 times the median absolute deviation (MAD), which is ~25 times more than listed in the ANSS catalog. The aftershock rate generally decayed with time as predicted by the Omori's law. A statistically significant increase of seismicity rate is found when hurricane Irene passed by the epicentral region. A possible explanation is that the atmosphere pressure drop unloaded the surface, which brought the reverse faults closer to failure. However, we also identified similar fluctuations of seismicity rate changes at other times. Hence, it is still

  6. The Al Hoceima Mw 6.4 earthquake of 24 February 2004 and its aftershocks sequence

    NASA Astrophysics Data System (ADS)

    van der Woerd, Jérôme; Dorbath, Catherine; Ousadou, Farida; Dorbath, Louis; Delouis, Bertrand; Jacques, Eric; Tapponnier, Paul; Hahou, Youssef; Menzhi, Mohammed; Frogneux, Michel; Haessler, Henri

    2014-07-01

    The Al Hoceima Mw 6.4 earthquake of 24 February 2004 that occurred in the eastern Rif region of Morocco already hit by a large event in May 1994 (Mw 5.9) has been followed by numerous aftershocks in the months following the event. The aftershock sequence has been monitored by a temporary network of 17 autonomous seismic stations during 15 days (28 March-10 April) in addition to 5 permanent stations of the Moroccan seismic network (CNRST, SPG, Rabat). This network allowed locating accurately about 650 aftershocks that are aligned in two directions, about N10-20E and N110-120E, in rough agreement with the two nodal planes of the focal mechanism (Harvard). The aftershock alignments are long enough, about 20 km or more, to correspond both to the main rupture plane. To further constrain the source of the earthquake main shock and aftershocks (mb > 3.5) have been relocated thanks to regional seismic data from Morocco and Spain. While the main shock is located at the intersection of the aftershock clouds, most of the aftershocks are aligned along the N10-20E direction. This direction together with normal sinistral slip implied by the focal mechanism is similar with the direction and mechanisms of active faults in the region, particularly the N10E Trougout oblique normal fault. Indeed, the Al Hoceima region is dominated by an approximate ENE-SSW direction of extension, with oblique normal faults. Three major 10-30 km-long faults, oriented NNE-SSW to NW-SE are particularly clear in the morphology, the Ajdir and Trougout faults, west and east of the Al Hoceima basin, respectively, and the NS Rouadi fault 20 km to the west. These faults show clear evidence of recent vertical displacements during the late Quaternary such as uplifted alluvial terraces along Oued Rihs, offset fan surfaces by the Rouadi fault and also uplifted and tilted abandoned marine terraces on both sides of the Al Hoceima bay. However, the N20E direction is in contrast with seismic sources identified from

  7. Anomalous stress diffusion, Omori's law and Continuous Time Random Walk in the 2010 Efpalion aftershock sequence (Corinth rift, Greece)

    NASA Astrophysics Data System (ADS)

    Michas, Georgios; Vallianatos, Filippos; Karakostas, Vassilios; Papadimitriou, Eleftheria; Sammonds, Peter

    2014-05-01

    Efpalion aftershock sequence occurred in January 2010, when an M=5.5 earthquake was followed four days later by another strong event (M=5.4) and numerous aftershocks (Karakostas et al., 2012). This activity interrupted a 15 years period of low to moderate earthquake occurrence in Corinth rift, where the last major event was the 1995 Aigion earthquake (M=6.2). Coulomb stress analysis performed in previous studies (Karakostas et al., 2012; Sokos et al., 2012; Ganas et al., 2013) indicated that the second major event and most of the aftershocks were triggered due to stress transfer. The aftershocks production rate decays as a power-law with time according to the modified Omori law (Utsu et al., 1995) with an exponent larger than one for the first four days, while after the occurrence of the second strong event the exponent turns to unity. We consider the earthquake sequence as a point process in time and space and study its spatiotemporal evolution considering a Continuous Time Random Walk (CTRW) model with a joint probability density function of inter-event times and jumps between the successive earthquakes (Metzler and Klafter, 2000). Jump length distribution exhibits finite variance, whereas inter-event times scale as a q-generalized gamma distribution (Michas et al., 2013) with a long power-law tail. These properties are indicative of a subdiffusive process in terms of CTRW. Additionally, the mean square displacement of aftershocks is constant with time after the occurrence of the first event, while it changes to a power-law with exponent close to 0.15 after the second major event, illustrating a slow diffusive process. During the first four days aftershocks cluster around the epicentral area of the second major event, while after that and taking as a reference the second event, the aftershock zone is migrating slowly with time to the west near the epicentral area of the first event. This process is much slower from what would be expected from normal diffusion, a

  8. Seismological aspects of the 27 June 2015 Gulf of Aqaba earthquake and its sequence of aftershocks

    NASA Astrophysics Data System (ADS)

    Abd el-aal, Abd el-aziz Khairy; Badreldin, Hazem

    2016-07-01

    On 27 June 2015, a moderate earthquake with magnitude Mb 5.2 struck the Gulf of Aqaba near Nuweiba City. This event was instrumentally recorded by the Egyptian National Seismic Network (ENSN) and many other international seismological centres. The event was felt in all the cities on the Gulf of Aqaba, as well as Suez City, Hurghada City, the greater Cairo Metropolitan Area, Israel, Jordan and the north-western part of Saudi Arabia. No casualties were reported, however. Approximately 95 aftershocks with magnitudes ranging from 0.7 to 4.2 were recorded by the ENSN following the mainshock. In the present study, the source characteristics of both the mainshock and the aftershocks were estimated using the near-source waveform data recorded by the very broadband stations of the ENSN, and these were validated by the P-wave polarity data from short period stations. Our analysis reveals that an estimated seismic moment of 0.762 × 1017 Nm was released, corresponding to a magnitude of Mw 5.2, a focal depth of 14 km, a fault radius of 0.72 km and a rupture area of approximately 1.65 km2. Monitoring the sequence of aftershocks reveals that they form a cluster around the mainshock and migrated downwards in focal depth towards the west. We compared the results we obtained with the published results from the international seismological centres. Our results are more realistic and accurate, in particular with respect to the epicenteral location, magnitude and fault plane solution which are in accordance with the hypocentre distribution of the aftershocks.

  9. An Autonomous System for Grouping Events in a Developing Aftershock Sequence

    SciTech Connect

    Harris, D. B.; Dodge, D. A.

    2011-03-22

    We describe a prototype detection framework that automatically clusters events in real time from a rapidly unfolding aftershock sequence. We use the fact that many aftershocks are repetitive, producing similar waveforms. By clustering events based on correlation measures of waveform similarity, the number of independent event instances that must be examined in detail by analysts may be reduced. Our system processes array data and acquires waveform templates with a short-term average (STA)/long-term average (LTA) detector operating on a beam directed at the P phases of the aftershock sequence. The templates are used to create correlation-type (subspace) detectors that sweep the subsequent data stream for occurrences of the same waveform pattern. Events are clustered by association with a particular detector. Hundreds of subspace detectors can run in this framework a hundred times faster than in real time. Nonetheless, to check the growth in the number of detectors, the framework pauses periodically and reclusters detections to reduce the number of event groups. These groups define new subspace detectors that replace the older generation of detectors. Because low-magnitude occurrences of a particular signal template may be missed by the STA/LTA detector, we advocate restarting the framework from the beginning of the sequence periodically to reprocess the entire data stream with the existing detectors. We tested the framework on 10 days of data from the Nevada Seismic Array (NVAR) covering the 2003 San Simeon earthquake. One hundred eighty-four automatically generated detectors produced 676 detections resulting in a potential reduction in analyst workload of up to 73%.

  10. Implications of spatial and temporal development of the aftershock sequence for the Mw 8.3 June 9, 1994 Deep Bolivian Earthquake

    NASA Astrophysics Data System (ADS)

    Myers, Stephen C.; Wallace, Terry C.; Beck, Susan L.; Silver, Paul G.; Zandt, George; Vandecar, John; Minaya, Estela

    On June 9, 1994 the Mw 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks (m > 2.2) for the 20-day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a mb ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east-southeast of the mainshock at a depth of 671 km. The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N-S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.

  11. The 2009 L'Aquila sequence (Central Italy): fault system anatomy by aftershock distribution.

    NASA Astrophysics Data System (ADS)

    Chiaraluce, Lauro

    2010-05-01

    On April 6 (01:32 UTC) 2009 a destructive MW 6.13 earthquake struck the Abruzzi region in Central Italy, causing nearly 300 deaths, 40.000 homeless people and strong damage to the cultural heritage of the L'Aquila city and its province. Two strong earthquakes hit the same area in historical times (e.g. the 1461 and 1703 events), but the main fault that drives the extension in this portion of the Apennines was unknown. Seismic data was recorded at both permanent stations of the Centralised Italian National Seismic Network managed by the INGV and 45 temporary stations installed in the epicentral area together with the LGIT of Grenoble (Fr). The resulting geometry of the dense monitoring network allows us to gain very high resolution earthquake locations that we use to investigate the geometry of the activated fault system and to report on seismicity pattern and kinematics of the whole sequence. The mainshock was preceded by a foreshock sequence that activated the main fault plane during the three months before, while the largest foreshock (MW 4.08) occurred one week before (30th of March) nucleated on a antithetic (e.g. off-fault) segment. The distribution of the aftershocks defines a complex, 50 km long, NW-trending normal fault system, with seismicity nucleating within the upper 10-12 km of the crust. There is an exception of an event (MW 5.42) nucleating a couple of kilometers deeper that the 7th of April that activates a high angle normal fault antithetic to the main system. Its role is still unclear. We reconstruct the geometry of the two major SW-dipping normal faults forming a right lateral en-echelon system. The main fault (L'Aquila fault) is activated by the 6th of April mainshock unluckily located right below the city of L'Aquila. A 50°SW-dipping plane with planar geometry about 16 km long. The related seismicity interests the entire first 12 km of the upper crust from the surface. The ground surveys carried out soon after the occurrence of the earthquake

  12. Exploring the Limits of Waveform Correlation Event Detection as Applied to Three Earthquake Aftershock Sequences

    NASA Astrophysics Data System (ADS)

    Young, C. J.; Carr, D.; Resor, M.; Duffey, S.

    2009-12-01

    Swarms of earthquakes and/or aftershock sequences can dramatically increase the level of seismicity in a region for a period of time lasting from days to months, depending on the swarm or sequence. Such occurrences can provide a large amount of useful information to seismologists. For those who monitor seismic events for possible nuclear explosions, however, these swarms/sequences are a nuisance. In an explosion monitoring system, each event must be treated as a possible nuclear test until it can be proven, to a high degree of confidence, not to be. Seismic events recorded by the same station with highly correlated waveforms almost certainly have a similar location and source type, so clusters of events within a swarm can quickly be identified as earthquakes. We have developed a number of tools that can be used to exploit the high degree of waveform similarity expected to be associated with swarms/sequences. Dendro Tool measures correlations between known events. The Waveform Correlation Detector is intended to act as a detector, finding events in raw data which correlate with known events. The Self Scanner is used to find all correlated segments within a raw data steam and does not require an event library. All three techniques together provide an opportunity to study the similarities of events in an aftershock sequence in different ways. To comprehensively characterize the benefits and limits of waveform correlation techniques, we studied 3 aftershock sequences, using our 3 tools, at multiple stations. We explored the effects of station distance and event magnitudes on correlation results. Lastly, we show the reduction in detection threshold and analyst workload offered by waveform correlation techniques compared to STA/LTA based detection. We analyzed 4 days of data from each aftershock sequence using all three methods. Most known events clustered in a similar manner across the toolsets. Up to 25% of catalogued events were found to be a member of a cluster. In

  13. The variability of PSV response spectra across a dense array deployed during the Northridge aftershock sequence

    USGS Publications Warehouse

    Field, E.H.; Hough, S.E.

    1997-01-01

    This study addresses the variability of pseudo-velocity response spectra across an array deployed on stiff soil in the San Fernando Valley during the Northridge (Mw 6.7) aftershock sequence. The separation between stations ranged from 0.5 to 5 km, and the aftershock magnitudes ranged from 2.3 to 4.0. We find that 95-percent of observed response spectra are within a factor of 1.9 to 2.6 of the network average. Statistically significant relative amplification factors were found for some of the sites, but the variability of observed response spectra is not significantly reduced by correcting for these effects. This implies that microzonation efforts on less than 5-km distance scales are not warranted at these types of sites. We also found a distance dependence for the response-spectral variability between neighboring sites. 95-percent are within a factor of ???2.3 at 0.5 km, increasing to 95-percent within a factor of ???4.2 at 5 km. No frequency dependence in these values could be resolved. Additional work is needed to examine the influence of other factors such as earthquake magnitude.

  14. Long aftershock sequences in North China and Central US: implications for hazard assessment in mid-continents

    NASA Astrophysics Data System (ADS)

    Liu, Mian; Luo, Gang; Wang, Hui; Stein, Seth

    2014-02-01

    Because seismic activity within mid-continents is usually much lower than that along plate boundary zones, even small earthquakes can cause widespread concerns, especially when these events occur in the source regions of previous large earthquakes. However, these small earthquakes may be just aftershocks that continue for decades or even longer. The recent seismicity in the Tangshan region in North China is likely aftershocks of the 1976 Great Tangshan earthquake. The current earthquake sequence in the New Madrid seismic zone in central United States, which includes a cluster of M ~ 7.0 events in 1811-1812 and a number of similar events in the past millennium, is believed to result from recent fault reactivation that releases pre-stored strain energy in the crust. If so, this earthquake sequence is similar to aftershocks in that the rates of energy release should decay with time and the sequence of earthquakes will eventually end. We use simple physical analysis and numerical simulations to show that the current sequence of large earthquakes in the New Madrid fault zone is likely ending or has ended. Recognizing that mid-continental earthquakes have long aftershock sequences and complex spatiotemporal occurrences are critical to improve hazard assessments.

  15. An explosion aftershock model with application to on-site inspection

    SciTech Connect

    Ford, Sean R.; Labak, Peter

    2015-02-14

    An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using an aftershock rate model. The model is developed with data from the Nevada National Security Site, formerly known as the Nevada Test Site, and the Semipalatinsk Test Site, which we take to represent soft-rock and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help inform the Seismic Aftershock Monitoring System (SAMS) deployment in a potential Comprehensive Test Ban Treaty On-Site Inspection (OSI), by giving the OSI team a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment, combined with an estimate of the background seismicity in the IA and an empirically derived map of threshold magnitude for the SAMS network, could aid the OSI team in reporting. Here, we apply the hard-rock model to a M5 event and combine it with the very sensitive detection threshold for OSI sensors to show that tens of events per day are expected up to a month after an explosion measured several kilometers away.

  16. An explosion aftershock model with application to on-site inspection

    DOE PAGES

    Ford, Sean R.; Labak, Peter

    2015-02-14

    An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using an aftershock rate model. The model is developed with data from the Nevada National Security Site, formerly known as the Nevada Test Site, and the Semipalatinsk Test Site, which we take to represent soft-rock and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help inform the Seismic Aftershock Monitoring System (SAMS) deployment in a potential Comprehensive Test Ban Treaty On-Site Inspection (OSI), by giving the OSI teammore » a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment, combined with an estimate of the background seismicity in the IA and an empirically derived map of threshold magnitude for the SAMS network, could aid the OSI team in reporting. Here, we apply the hard-rock model to a M5 event and combine it with the very sensitive detection threshold for OSI sensors to show that tens of events per day are expected up to a month after an explosion measured several kilometers away.« less

  17. An Explosion Aftershock Model with Application to On-Site Inspection

    NASA Astrophysics Data System (ADS)

    Ford, Sean R.; Labak, Peter

    2016-01-01

    An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using an aftershock rate model. The model is developed with data from the Nevada National Security Site, formerly known as the Nevada Test Site, and the Semipalatinsk Test Site, which we take to represent soft-rock and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help inform the Seismic Aftershock Monitoring System (SAMS) deployment in a potential Comprehensive Test Ban Treaty On-Site Inspection (OSI), by giving the OSI team a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment, combined with an estimate of the background seismicity in the IA and an empirically derived map of threshold magnitude for the SAMS network, could aid the OSI team in reporting. We apply the hard-rock model to a M5 event and combine it with the very sensitive detection threshold for OSI sensors to show that tens of events per day are expected up to a month after an explosion measured several kilometers away.

  18. Aftershock Characteristics as a Means of Discriminating Explosions from Earthquakes

    SciTech Connect

    Ford, S R; Walter, W R

    2009-05-20

    The behavior of aftershock sequences around the Nevada Test Site in the southern Great Basin is characterized as a potential discriminant between explosions and earthquakes. The aftershock model designed by Reasenberg and Jones (1989, 1994) allows for a probabilistic statement of earthquake-like aftershock behavior at any time after the mainshock. We use this model to define two types of aftershock discriminants. The first defines M{sub X}, or the minimum magnitude of an aftershock expected within a given duration after the mainshock with probability X. Of the 67 earthquakes with M > 4 in the study region, 63 of them produce an aftershock greater than M{sub 99} within the first seven days after a mainshock. This is contrasted with only six of 93 explosions with M > 4 that produce an aftershock greater than M{sub 99} for the same period. If the aftershock magnitude threshold is lowered and the M{sub 90} criteria is used, then no explosions produce an aftershock greater than M{sub 90} for durations that end more than 17 days after the mainshock. The other discriminant defines N{sub X}, or the minimum cumulative number of aftershocks expected for given time after the mainshock with probability X. Similar to the aftershock magnitude discriminant, five earthquakes do not produce more aftershocks than N{sub 99} within 7 days after the mainshock. However, within the same period all but one explosion produce less aftershocks then N{sub 99}. One explosion is added if the duration is shortened to two days after than mainshock. The cumulative number aftershock discriminant is more reliable, especially at short durations, but requires a low magnitude of completeness for the given earthquake catalog. These results at NTS are quite promising and should be evaluated at other nuclear test sites to understand the effects of differences in the geologic setting and nuclear testing practices on its performance.

  19. Power-law rheology controls aftershock triggering and decay

    PubMed Central

    Zhang, Xiaoming; Shcherbakov, Robert

    2016-01-01

    The occurrence of aftershocks is a signature of physical systems exhibiting relaxation phenomena. They are observed in various natural or experimental systems and usually obey several non-trivial empirical laws. Here we consider a cellular automaton realization of a nonlinear viscoelastic slider-block model in order to infer the physical mechanisms of triggering responsible for the occurrence of aftershocks. We show that nonlinear viscoelasticity plays a critical role in the occurrence of aftershocks. The model reproduces several empirical laws describing the statistics of aftershocks. In case of earthquakes, the proposed model suggests that the power-law rheology of the fault gauge, underlying lower crust, and upper mantle controls the decay rate of aftershocks. This is verified by analysing several prominent aftershock sequences for which the rheological properties of the underlying crust and upper mantle were established. PMID:27819355

  20. Power-law rheology controls aftershock triggering and decay

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoming; Shcherbakov, Robert

    2016-11-01

    The occurrence of aftershocks is a signature of physical systems exhibiting relaxation phenomena. They are observed in various natural or experimental systems and usually obey several non-trivial empirical laws. Here we consider a cellular automaton realization of a nonlinear viscoelastic slider-block model in order to infer the physical mechanisms of triggering responsible for the occurrence of aftershocks. We show that nonlinear viscoelasticity plays a critical role in the occurrence of aftershocks. The model reproduces several empirical laws describing the statistics of aftershocks. In case of earthquakes, the proposed model suggests that the power-law rheology of the fault gauge, underlying lower crust, and upper mantle controls the decay rate of aftershocks. This is verified by analysing several prominent aftershock sequences for which the rheological properties of the underlying crust and upper mantle were established.

  1. The 2016 Kumamoto-Oita earthquake sequence: aftershock seismicity gap and dynamic triggering in volcanic areas

    NASA Astrophysics Data System (ADS)

    Uchide, Takahiko; Horikawa, Haruo; Nakai, Misato; Matsushita, Reiken; Shigematsu, Norio; Ando, Ryosuke; Imanishi, Kazutoshi

    2016-11-01

    The 2016 Kumamoto-Oita earthquake sequence involving three large events ( M w ≥ 6) in the central Kyushu Island, southwest Japan, activated seismicities in two volcanic areas with unusual and puzzling spatial gaps after the largest earthquake ( M w 7.0) of April 16, 2016. We attempt to reveal the seismic process during the sequence by following seismological data analyses. Our hypocenter relocation result implies that the large events ruptured different faults of a complex fault system. A slip inversion analysis of the largest event indicates a large slip in the seismicity gap (Aso gap) in the caldera of Mt. Aso, which probably released accumulated stress and resulted in little aftershock production. We identified that the largest event dynamically triggered a mid-M6 event at Yufuin (80 km northeast of the epicenter), which is consistent with existence of the 20-km long zone where seismicity was activated and surface offset was observed. These findings will help us study the contribution of the identified complexity in fault geometries and the geotherm in the volcanic areas to the revealed seismic process and consequently improve our understanding of the seismo-volcano tectonics.[Figure not available: see fulltext.

  2. Bayesian Predictive Distribution for the Magnitude of the Largest Aftershock

    NASA Astrophysics Data System (ADS)

    Shcherbakov, R.

    2014-12-01

    Aftershock sequences, which follow large earthquakes, last hundreds of days and are characterized by well defined frequency-magnitude and spatio-temporal distributions. The largest aftershocks in a sequence constitute significant hazard and can inflict additional damage to infrastructure. Therefore, the estimation of the magnitude of possible largest aftershocks in a sequence is of high importance. In this work, we propose a statistical model based on Bayesian analysis and extreme value statistics to describe the distribution of magnitudes of the largest aftershocks in a sequence. We derive an analytical expression for a Bayesian predictive distribution function for the magnitude of the largest expected aftershock and compute the corresponding confidence intervals. We assume that the occurrence of aftershocks can be modeled, to a good approximation, by a non-homogeneous Poisson process with a temporal event rate given by the modified Omori law. We also assume that the frequency-magnitude statistics of aftershocks can be approximated by Gutenberg-Richter scaling. We apply our analysis to 19 prominent aftershock sequences, which occurred in the last 30 years, in order to compute the Bayesian predictive distributions and the corresponding confidence intervals. In the analysis, we use the information of the early aftershocks in the sequences (in the first 1, 10, and 30 days after the main shock) to estimate retrospectively the confidence intervals for the magnitude of the expected largest aftershocks. We demonstrate by analysing 19 past sequences that in many cases we are able to constrain the magnitudes of the largest aftershocks. For example, this includes the analysis of the Darfield (Christchurch) aftershock sequence. The proposed analysis can be used for the earthquake hazard assessment and forecasting associated with the occurrence of large aftershocks. The improvement in instrumental data associated with early aftershocks can greatly enhance the analysis and

  3. The 25 March 1993 Scotts Mills, Oregon, earthquake and aftershock sequence: Spatial distribution, focal mechanisms, and the mount angel fault

    USGS Publications Warehouse

    Thomas, G.C.; Crosson, R.S.; Carver, D.L.; Yelin, T.S.

    1996-01-01

    The 25 March 1993 ML = 5.7 crustal earthquake near Scotts Mills, Oregon, was the largest earthquake to occur in the Pacific Northwest in over a decade. The mainshock was located at 45.033?? N, 122.586?? W and at a depth of about 15.1 km, based on arrival time data from the short-period Pacific Northwest Seismograph Network. Beginning about 12 h after the mainshock, investigators from the U.S. Geological Survey deployed 22 digital seismographs to record aftershocks. Using data from the temporary and permanent stations, we analyzed a subset of 50 after-shocks with quality locations. Hypocenters of these aftershocks lie on a northwesttrending steeply dipping plane (strike 290 ?? 10??, dipping 60 ?? 5?? to the north-northeast), in agreement with the preferred slip plane of the mainshock focal mechanism solution (strike 294??, dipping 58?? to the north-northeast). The planar structure defined by the aftershock locations may be a southeast continuation of the Mount Angel Fault, a reverse fault identified from both surface and subsurface evidence. The mapped southeast extent of the Mount Angel Fault is located less than 10 km west of the Scotts Mills epicentral region. In addition, the mainshock focal mechanism solution, with a combination of reverse motion and right-lateral strike slip, has a geometry and sense of motion consistent with the Mount Angel Fault. While aftershock focal mechanisms are varied, P axes are consistently oriented in a subhorizontal north-south direction. This earthquake sequence, together with the geological and geophysical evidence for the Mount Angel Fault, suggests a significant crustal earthquake hazard for this region of northwest Oregon.

  4. Distribution of the largest aftershocks in branching models of triggered seismicity: theory of the universal Båth law.

    PubMed

    Saichev, A; Sornette, D

    2005-05-01

    Using the epidemic-type aftershock sequence (ETAS) branching model of triggered seismicity, we apply the formalism of generating probability functions to calculate exactly the average difference between the magnitude of a mainshock and the magnitude of its largest aftershock over all generations. This average magnitude difference is found empirically to be independent of the mainshock magnitude and equal to 1.2, a universal behavior known as Båth's law. Our theory shows that Båth's law holds only sufficiently close to the critical regime of the ETAS branching process. Allowing for error bars +/- 0.1 for Båth's constant value around 1.2, our exact analytical treatment of Båth's law provides new constraints on the productivity exponent alpha and the branching ratio n: 0.9 approximately < alpha < or =1. We propose a method for measuring alpha based on the predicted renormalization of the Gutenberg-Richter distribution of the magnitudes of the largest aftershock. We also introduce the "second Båth law for foreshocks:" the probability that a main earthquake turns out to be the foreshock does not depend on its magnitude rho.

  5. The Hellenic Seismological Network of Crete (HSNC): validation and results of the 2013 aftershock sequences

    NASA Astrophysics Data System (ADS)

    Chatzopoulos, G.; Papadopoulos, I.; Vallianatos, F.

    2016-02-01

    The last century, the global urbanization has leaded the majority of population to move into big, metropolitan areas. Small areas on the Earth's surface are being built with tall buildings in areas close to seismogenic zones. Such an area of great importance is the Hellenic arc in Greece. Among the regions with high seismicity is Crete, located on the subduction zone of the Eastern Mediterranean plate underneath the Aegean plate. The Hellenic Seismological Network of Crete (HSNC) has been built to cover the need on continuous monitoring of the regional seismicity in the vicinity of the South Aegean Sea and Crete Island. In the present work, with the use of Z-map software the spatial variability of Magnitude of Completeness (Mc) is calculated from HSNC's manual analysis catalogue of events from the beginning of 2008 till the end of September 2015, supporting the good coverage of HSNC in the area surrounding Crete Island. Furthermore, we discuss the 2013 seismicity when two large earthquakes occurred in the vicinity of Crete Island. The two main shocks and their aftershock sequences have been relocated with the use of HYPOINVERSE earthquake location software. Finally, the quality of seismological stations is addressed using the standard PQLX software.

  6. Aftershocks and Omori's law in a modified Carlson-Langer model with nonlinear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Okamura, Kazuki

    2015-05-01

    A modified Carlson-Langer model for earthquakes is proposed, which includes nonlinear viscoelasticity. Several aftershocks are generated after the main shock owing to the damping of the additional viscoelastic force. Both the Gutenberg-Richter law and Omori's law are reproduced in a numerical simulation of the modified Carlson-Langer model on a critical percolation cluster of a square lattice.

  7. Damped regional-scale stress inversions: Methodology and examples for southern California and the Coalinga aftershock sequence

    USGS Publications Warehouse

    Hardebeck, J.L.; Michael, A.J.

    2006-01-01

    We present a new focal mechanism stress inversion technique to produce regional-scale models of stress orientation containing the minimum complexity necessary to fit the data. Current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea. This procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor. To remove these artifacts while retaining any stress variations that are strongly required by the data, we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas. This method is conceptually similar to other geophysical inverse techniques that incorporate damping, such as seismic tomography. In checkerboard tests, the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion, while resolving sharper true stress rotations than a simple smoothed model or a moving-window inversion. We show an example of a spatially damped stress field for southern California. The methodology can also be used to study temporal stress changes, and an example for the Coalinga, California, aftershock sequence is shown. We recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field.

  8. Aftershock Energy Distribution by Statistical Mechanics Approach

    NASA Astrophysics Data System (ADS)

    Daminelli, R.; Marcellini, A.

    2015-12-01

    The aim of our work is to research the most probable distribution of the energy of aftershocks. We started by applying one of the fundamental principles of statistical mechanics that, in case of aftershock sequences, it could be expressed as: the greater the number of different ways in which the energy of aftershocks can be arranged among the energy cells in phase space the more probable the distribution. We assume that each cell in phase space has the same possibility to be occupied, and that more than one cell in the phase space can have the same energy. Seeing that seismic energy is proportional to products of different parameters, a number of different combinations of parameters can produce different energies (e.g., different combination of stress drop and fault area can release the same seismic energy). Let us assume that there are gi cells in the aftershock phase space characterised by the same energy released ɛi. Therefore we can assume that the Maxwell-Boltzmann statistics can be applied to aftershock sequences with the proviso that the judgment on the validity of this hypothesis is the agreement with the data. The aftershock energy distribution can therefore be written as follow: n(ɛ)=Ag(ɛ)exp(-βɛ)where n(ɛ) is the number of aftershocks with energy, ɛ, A and β are constants. Considering the above hypothesis, we can assume g(ɛ) is proportional to ɛ. We selected and analysed different aftershock sequences (data extracted from Earthquake Catalogs of SCEC, of INGV-CNT and other institutions) with a minimum magnitude retained ML=2 (in some cases ML=2.6) and a time window of 35 days. The results of our model are in agreement with the data, except in the very low energy band, where our model resulted in a moderate overestimation.

  9. Application of Subspace Detection to the 6 November 2011 M5.6 Prague, Oklahoma Aftershock Sequence

    NASA Astrophysics Data System (ADS)

    McMahon, N. D.; Benz, H.; Johnson, C. E.; Aster, R. C.; McNamara, D. E.

    2015-12-01

    Subspace detection is a powerful tool for the identification of small seismic events. Subspace detectors improve upon single-event matched filtering techniques by using multiple orthogonal waveform templates whose linear combinations characterize a range of observed signals from previously identified earthquakes. Subspace detectors running on multiple stations can significantly increasing the number of locatable events, lowering the catalog's magnitude of completeness and thus providing extraordinary detail on the kinematics of the aftershock process. The 6 November 2011 M5.6 earthquake near Prague, Oklahoma is the largest earthquake instrumentally recorded in Oklahoma history and the largest earthquake resultant from deep wastewater injection. A M4.8 foreshock on 5 November 2011 and the M5.6 mainshock triggered tens of thousands of detectable aftershocks along a 20 km splay of the Wilzetta Fault Zone known as the Meeker-Prague fault. In response to this unprecedented earthquake, 21 temporary seismic stations were deployed surrounding the seismic activity. We utilized a catalog of 767 previously located aftershocks to construct subspace detectors for the 21 temporary and 10 closest permanent seismic stations. Subspace detection identified more than 500,000 new arrival-time observations, which associated into more than 20,000 locatable earthquakes. The associated earthquakes were relocated using the Bayesloc multiple-event locator, resulting in ~7,000 earthquakes with hypocentral uncertainties of less than 500 m. The relocated seismicity provides unique insight into the spatio-temporal evolution of the aftershock sequence along the Wilzetta Fault Zone and its associated structures. We find that the crystalline basement and overlying sedimentary Arbuckle formation accommodate the majority of aftershocks. While we observe aftershocks along the entire 20 km length of the Meeker-Prague fault, the vast majority of earthquakes were confined to a 9 km wide by 9 km deep

  10. Spatial stress variations in the aftershock sequence following the 2008 M6 earthquake doublet in the South Iceland Seismic Zone

    NASA Astrophysics Data System (ADS)

    Hensch, M.; Árnadóttir, Th.; Lund, B.; Brandsdóttir, B.

    2012-04-01

    The South Iceland Seismic Zone (SISZ) is an approximately 80 km wide E-W transform zone, bridging the offset between the Eastern Volcanic Zone and the Hengill triple junction to the west. The plate motion is accommodated in the brittle crust by faulting on many N-S trending right-lateral strike-slip faults of 2-5 km separation. Major sequences of large earthquakes (M>6) has occurred repeatedly in the SISZ since the settlement in Iceland more than thousand years ago. On 29th May 2008, two M6 earthquakes hit the western part of the SISZ on two adjacent N-S faults within a few seconds. The intense aftershock sequence was recorded by the permanent Icelandic SIL network and a promptly installed temporary network of 11 portable seismometers in the source region. The network located thousands of aftershocks during the following days, illuminating a 12-17 km long region along both major fault ruptures as well as several smaller parallel faults along a diffuse E-W trending region west of the mainshock area without any preceding main rupture. This episode is suggested to be the continuation of an earthquake sequence which started with two M6.5 and several M5-6 events in June 2000. The time delay between the 2000 and 2008 events could be due to an inflation episode in Hengill during 1993-1998, that potentially locked N-S strike slip faults in the western part of the SISZ. Around 300 focal solutions for aftershocks have been derived by analyzing P-wave polarities, showing predominantly strike-slip movements with occasional normal faulting components (unstable P-axis direction), which suggests an extensional stress regime as their driving force. A subsequent stress inversion of four different aftershock clusters reveals slight variations of the directions of the average σ3 axes. While for both southern clusters, including the E-W cluster, the σ3 axes are rather elongated perpendicular to the overall plate spreading axis, they are more northerly trending for shallower clusters

  11. Are aftershocks caused by the mainshock?

    NASA Astrophysics Data System (ADS)

    Daminelli, Rosastella; Marcellini, Alberto

    2016-04-01

    Understanding the physics of aftershocks bears the question: are aftershocks caused by the stress modification induced by the mainshock or by other shocks of the seismic sequence? This causality principle (henceforth called Hypothesis 1) constitutes the base of several aftershock models. An alternative point of view is that both mainshock and aftershocks belong to the fracture process, both of which are related to the stress of the zone however there is no particular relationship between them (henceforth called Hypothesis 2). The May-June 2012 Emilia-Lombardia earthquake was characterised by two major events with magnitude of 5.9 and 5.8 respectively, and other 5 shocks with magnitude greater than 5. This sequence does not allow for a precise identification of the mainshock and strongly undermines Hypothesis 1. We can verify that the Maxwell-Boltzmann model for statistical energy distribution of independent particles agrees with the energy distribution of the shocks of the 2012 Emilia-Lombardia earthquake, as well as with other seismic sequences, randomly selected from international seismic databases. Thus suggesting that the shocks of a sequence can be considered independent events. Our conclusions are that the distinction made between foreshock, mainshock and aftershocks for several sequences is fictitious and that Hypothesis 2 is more realistic.

  12. Detailed velocity ratio mapping during the aftershock sequence as a tool to monitor the fluid activity within the fault plane

    NASA Astrophysics Data System (ADS)

    Bachura, Martin; Fischer, Tomáš

    2016-11-01

    The rheological properties of Earth materials are expressed by their seismic velocities and VP /VS ratio, which is easily obtained by the Wadati method. Its double-difference version based on cross-correlated waveforms enables focusing on very local structures and allows tracking, monitoring and analysing the fluid activity along faults. We applied the method to three 2014 mainshock-aftershock sequences in the West Bohemia/Vogtland (Czech Republic) earthquake swarm area and found pronounced VP /VS variations in time and space for different clusters of events located on a steeply dipping fault zone at depths ranging from 7 to 11 km. Each cluster reflects the spatial distribution of earthquakes along the fault plane but also the temporal evolution of the activity. Low values of VP /VS ratio down to 1.59 ± 0.02 were identified in the deeper part of the fault zone whereas higher values up to 1.73 ± 0.01 were estimated for clusters located on a shallower segment of the fault. Temporally the low VP /VS values are associated with the early aftershocks, while the higher VP /VS ratios are related only to later aftershocks. We interpret this behaviour as a result of saturation of the focal zone by compressible fluids: in the beginning the mainshock and early aftershocks driven by over-pressured fluids increased the porosity due to opening the fluid pathways. This process was associated with a decrease of the velocity ratio. In later stages the pressure and porosity decreased and the velocity ratio recovered to levels of 1.73, typical for a Poissonian medium and Earth's crust.

  13. The 2012 August 11 MW 6.5, 6.4 Ahar-Varzghan earthquakes, NW Iran: aftershock sequence analysis and evidence for activity migration

    NASA Astrophysics Data System (ADS)

    Rezapour, Mehdi

    2016-02-01

    The Ahar-Varzghan doublet earthquakes with magnitudes MW 6.5 and 6.4 occurred on 2012 August 11 in northwest Iran and were followed by many aftershocks. In this paper, we analyse ˜5 months of aftershocks of these events. The Ahar-Varzghan earthquakes occurred along complex faults and provide a new constraint on the earthquake hazard in northwest Iran. The general pattern of relocated aftershocks defines a complex seismic zone covering an area of approximately 25 × 10 km2. The Ahar-Varzghan aftershock sequence shows a secondary activity which started on November 7, approximately 3 months after the main shocks, with a significant increase in activity, regarding both number of events and their magnitude. This stage was characterized by a seismic zone that propagated to the west of the main shocks. The catalogue of aftershocks for the doublet earthquake has a magnitude completeness of Mc 2.0. A below-average b-value for the Ahar-Varzghan sequence indicates a structural heterogeneity in the fault plane and the compressive stress state of the region. Relocated aftershocks occupy a broad zone clustering east-west with near-vertical dip which we interpret as the fault plane of the first of the doublet main shocks (MW 6.5). The dominant depth range of the aftershocks is from 3 to about 20 km, and the focal depths decrease toward the western part of the fault. The aftershock activity has its highest concentration in the eastern and middle parts of the active fault, and tapers off toward the western part of the active fault segment, indicating mainly a unilateral rupture toward west.

  14. Non extensive statistical physics properties of the 2003 (Mw6.2), Lefkada, Ionian island Greece, aftershock sequence

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.; Karakostas, V.; Papadimitriou, E.

    2012-04-01

    On 14 August 2003, Lefkada Island (Central Ionian) was affected by an Mw=6.2 earthquake. Due to a dense temporary seismic network that operating immediately after the main shock occurrence, hundreds of aftershocks were recorded and located with high precision whereas relocation of the main shock and early strong aftershocks became also feasible. Thus, the spatio-temporal distribution of aftershocks onto the main and the neighboring fault segments was investigated in detail enabling the recognition of four distinctive seismicity clusters separated by less active patches. The aftershock spatiotemporal properties studied here using the concept of Non-Extensive Statistical Physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are estimated for the data set in each seismicity cluster and the analysis results to a value of the statistical thermodynamic qT and qD parameters for each cluster, where qT varies from 1.15 to 1.47 and qD from 0.5 to 0.77 for the interevent times and distances distributions respectively. These values confirm the complexity and non-additivity of the spatiotemporal evolution of seismicity and the usefulness of NESP in investigating such phenomena. The temporal structure is also discussed using the complementary to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that the temporal evolution of the Lefkada aftershock sequence in clusters A, B and C governed by very low number of degrees of freedom while D is less organized seismicity structure with a much higher number of degrees of freedom. Acknowledgments. This work was supported in part by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive

  15. The Seismic source parameters of the 1991 Costa Rica aftershock sequence: Evidence for a transcurrent plate boundary

    NASA Astrophysics Data System (ADS)

    Gan, Guangwei; Beck, Susan L.; Wallace, Terry C.

    1993-09-01

    The April 22, 1991, Valle de la Estrella, Costa Rica earthquake (Ms=7.6) was a back-arc thrusting event associated with the underthrusting of the Caribbean plate beneath Central America. A network of three PASSCAL-type, portable instruments was deployed to monitor the aftershock activity in southern Costa Rica 2 to 6 weeks after the main shock. The waveforms recorded on three-component midperiod seismometers were used to recover source information for 15 small aftershocks (magnitudes between 3.2 and 4.4) with a linear moment tensor inversion method. We conducted several tests to investigate the effects of unknown structure and event mislocation on source parameter recovery. The longer-period waveforms, in general, are less sensitive to the effects of the structural details so that the essential source information can be successfully extracted from the waveform data. The earlier part of the seismic waveforms has proven to be the most important carrier of the source information. A gross crustal model can be used to describe the structure for the source study. The small changes in the waveform character resulting from the mislocation of the events, or inexact Green's functions generated from the oversimplified crustal model, do not prohibit us from the recovery of the source orientation at local distances. In contrast, the determination of the focal depth is subject to uncertainty because of the lack of detailed structural information. Our focal mechanisms are generally in good agreement with P wave first-motion fault plane solutions determined from a local short-period network. The aftershocks show a clear spatial segmentation based on focal mechanism type. Most aftershocks near or southeast of the main shock were thrusting events with focal mechanisms similar to the main shock. In contrast, a cluster of aftershocks northwest of the main shock showed dominantly left-lateral, strike-slip motion on a northeasterly striking nodal plane. This suggests that a diffuse

  16. Detection of the Wenchuan aftershock sequence using waveform correlation with a composite regional network

    SciTech Connect

    Slinkard, Megan; Heck, Stephen; Schaff, David; Bonal, Nedra; Daily, David; Young, Christopher; Richards, Paul

    2016-06-28

    Using template waveforms from aftershocks of the Wenchuan earthquake (12 May 2008, Ms 8.0) listed in a global bulletin and continuous data from eight regional stations, we detected more than 6000 additional events in the mainshock source region from 1 May to 12 August 2008. These new detections obey Omori’s law, extend the magnitude of completeness downward by 1.1 magnitude units, and lead to a more than fivefold increase in number of known aftershocks compared with the global bulletins published by the International Data Centre and the Inter national Seismological Centre. Moreover, we detected more M > 2 events than were listed by the Sichuan Seismograph Network. Several clusters of these detections were then relocated using the double-difference method, yielding locations that reduced travel-time residuals by a factor of 32 compared with the initial bulletin locations. Finally, our results suggest that using waveform correlation on a few regional stations can find aftershock events very effectively and locate them with precision.

  17. Detection of the Wenchuan aftershock sequence using waveform correlation with a composite regional network

    DOE PAGES

    Slinkard, Megan; Heck, Stephen; Schaff, David; ...

    2016-06-28

    Using template waveforms from aftershocks of the Wenchuan earthquake (12 May 2008, Ms 8.0) listed in a global bulletin and continuous data from eight regional stations, we detected more than 6000 additional events in the mainshock source region from 1 May to 12 August 2008. These new detections obey Omori’s law, extend the magnitude of completeness downward by 1.1 magnitude units, and lead to a more than fivefold increase in number of known aftershocks compared with the global bulletins published by the International Data Centre and the Inter national Seismological Centre. Moreover, we detected more M > 2 events thanmore » were listed by the Sichuan Seismograph Network. Several clusters of these detections were then relocated using the double-difference method, yielding locations that reduced travel-time residuals by a factor of 32 compared with the initial bulletin locations. Finally, our results suggest that using waveform correlation on a few regional stations can find aftershock events very effectively and locate them with precision.« less

  18. Characterization of Fault Networks and Diffusion of Aftershock Epicenters From Earthquake Catalogs: Fuzzy C-means Clustering and a Modified ETAS Model

    NASA Astrophysics Data System (ADS)

    Moulik, P.; Tiampo, K. F.

    2009-05-01

    The information on three-dimensional geometry as well as the identification of active fault segments is critical to our assessment of seismic risks. Numerical modeling of the aftershock locations, times and magnitudes are also crucial to characterize a fault zone. In this study, a pattern recognition technique based on the Fuzzy C- means clustering algorithm (Bezdek, 1981) is proposed to allow each earthquake to be associated with different fault segments. The spatial covariance tensor for each cluster and the associated earthquakes are used to find optimal anisotropic clusters and designate them as faults, similar to the OADC method (Ouillon et al., 2008). The location, size and orientation of the reconstructed faults segments are characterized using a fuzzy covariance matrix (Gustafson and Kessel, 1978). The output consists of a set of distinct fault segments along with the associated earthquakes at different fuzzy membership grades (Zadeh, 1965). A resultant matrix consists of the fuzzy membership grade for different earthquakes and corresponding faults segments specifying their degree of association with values from zero to one. The spatial distribution of earthquakes of different magnitudes and membership grades for a fault segment is incorporated in an anisotropic spatial kernel which characterizes the aftershock density at a distance vector in the ETAS model (Kagan and Knopoff, 1987; Ogata, 1988). An optimal spatio-temporal distribution of aftershocks is obtained for each fault segment without considering a priori distributions such as Gaussian or power law (Helmstetter et al., 2006; Helmstetter and Sornette, 2002). The model is tested on the aftershock sequence from the Denali, 2002 earthquake in Alaska and the fault reconstruction results compared with the known faults in the area. Therefore, a new method to incorporate the anisotropic nature of aftershock diffusion along with the reconstruction of fault networks from seismicity catalogs is formulated in

  19. 2010 Chile Earthquake Aftershock Response

    NASA Astrophysics Data System (ADS)

    Barientos, Sergio

    2010-05-01

    1906? Since the number of M>7.0 aftershocks has been low, does the distribution of large-magnitude aftershocks differ from previous events of this size? What is the origin of the extensional-type aftershocks at shallow depths within the upper plate? The international seismological community (France, Germany, U.K., U.S.A.) in collaboration with the Chilean seismological community responded with a total of 140 portable seismic stations to deploy in order to record aftershocks. This combined with the Chilean permanent seismic network, in the area results in 180 stations now in operation recording continuous at 100 cps. The seismic equipment is a mix of accelerometers, short -period and broadband seismic sensors deployed along the entire length of the aftershock zone that will record the aftershock sequence for three to six months. The collected seismic data will be merged and archived to produce an international data set open to the entire seismological community immediately after archiving. Each international group will submit their data as soon as possible in standard (mini seed) format with accompanying meta data to the IRIS DMC where the data will be merged into a combined data set and available to individuals and other data centers. This will be by far the best-recorded aftershock sequence of a large megathrust earthquake. This outstanding international collaboration will provide an open data set for this important earthquake as well as provide a model for future aftershock deployments around the world.

  20. Focal Depth of the WenChuan Earthquake Aftershocks from modeling of Seismic Depth Phases

    NASA Astrophysics Data System (ADS)

    Luo, Y.; Zeng, X.; Chong, J.; Ni, S.; Chen, Y.

    2008-12-01

    After the 05/12/2008 great WenChuan earthquake in Sichuan Province of China, tens of thousands earthquakes occurred with hundreds of them stronger than M4. Those aftershocks provide valuable information about seismotectonics and rupture processes for the mainshock, particularly accurate spatial distribution of aftershocks is very informational for determining rupture fault planes. However focal depth can not be well resolved just with first arrivals recorded by relatively sparse network in Sichuan Province, therefore 3D seismicity distribution is difficult to obtain though horizontal location can be located with accuracy of 5km. Instead local/regional depth phases such as sPmP, sPn, sPL and teleseismic pP,sP are very sensitive to depth, and be readily modeled to determine depth with accuracy of 2km. With reference 1D velocity structure resolved from receiver functions and seismic refraction studies, local/regional depth phases such as sPmP, sPn and sPL are identified by comparing observed waveform with synthetic seismograms by generalized ray theory and reflectivity methods. For teleseismic depth phases well observed for M5.5 and stronger events, we developed an algorithm in inverting both depth and focal mechanism from P and SH waveforms. Also we employed the Cut and Paste (CAP) method developed by Zhao and Helmberger in modeling mechanism and depth with local waveforms, which constrains depth by fitting Pnl waveforms and the relative weight between surface wave and Pnl. After modeling all the depth phases for hundreds of events , we find that most of the M4 earthquakes occur between 2-18km depth, with aftershocks depth ranging 4-12km in the southern half of Longmenshan fault while aftershocks in the northern half featuring large depth range up to 18km. Therefore seismogenic zone in the northern segment is deeper as compared to the southern segment. All the aftershocks occur in upper crust, given that the Moho is deeper than 40km, or even 60km west of the

  1. Full waveform modelling using the VERCE platform - application to aftershock seismicity in the Chile subduction zone

    NASA Astrophysics Data System (ADS)

    Garth, Thomas; Rietbrock, Andreas; Hicks, Steve; Fuenzalida Velasco, Amaya; Casarotti, Emanuele; Spinuso, Alessandro

    2015-04-01

    The VERCE platform is an online portal that allows full waveform simulations to be run for any region where a suitable velocity model exists. We use this facility to simulate the waveforms from aftershock earthquakes from the 2014 Pisagua earthquake, and 2010 Maule earthquake that occurred at the subduction zone mega thrust in Northern and Central Chile respectively. Simulations are performed using focal mechanisms from both global earthquake catalogues, and regional earthquake catalogues. The VERCE platform supports specFEM Cartesian, and simulations are run using meshes produced by CUBIT. The full waveform modelling techniques supported on the VERCE platform are used to test the validity of a number of subduction zone velocity models from the Chilean subduction zone. For the Maule earthquake we use a 2D and 3D travel time tomography model of the rupture area (Hicks et al. 2011; 2014). For the Pisagua earthquake we test a 2D/3D composite velocity model based on tomographic studies of the region (e.g. Husen et al. 2000, Contreyes-Reyes et al. 2012) and slab1.0 (Hayes et al. 2012). Focal mechanisms from the cGMT catalogue and local focal mechanisms calculated using ISOLA (e.g. Agurto et al. 2012) are used in the simulations. The waveforms produced are directly compared to waveforms recorded on the temporary deployment for the Maule earthquake aftershocks, and waveforms recorded on the IPOC network for the Pisagua earthquake aftershocks. This work demonstrates how the VERCE platform allows waveforms from the full 3D simulations to be easily produced, allowing us to quantify the validity of both the velocity model and the source mechanisms. These simulations therefore provide an independent test of the velocity models produced synthetically and by travel time tomography studies. Initial results show that the waveform is reasonably well reproduced in the 0.05 - 0.25 frequency band using a refined 3D travel time tomography, and locally calculated focal mechanisms.

  2. Evidence for static stress changes triggering the 1999 eruption of Cerro Negro Volcano, Nicaragua and regional aftershock sequences

    NASA Astrophysics Data System (ADS)

    Díez, M.; La Femina, P. C.; Connor, C. B.; Strauch, W.; Tenorio, V.

    2005-02-01

    Remarkable evidence of coupling between tectonic and magmatic events emerges from investigation of three tectonic earthquakes, aftershock sequences and eruption of Cerro Negro volcano, Nicaragua in 1999. Here, we explain this coupling through static stress changes following three Mw 5.2 earthquakes. We use focal mechanism solutions to estimate fault system geometry and magnitude of slip from these events, which are then used to calculate the change in minimum horizontal principal stress (σ3) for the region and the change in Coulomb failure stress on optimally oriented fault planes. Results of these simulations indicate that σ3 was reduced by ~0.08 MPa and that Coulomb failure stress was raised by 0.001 to 0.2 MPa in the region. A Kolmogorov-Smirnov test demonstrates spatial correlation of Coulomb failure stress changes and triggered seismicity and volcanism, and suggests that these small changes in static stress can trigger subsequent geophysical events under appropriate circumstances.

  3. Can We Forecast 1-Month Span Aftershock Activity from the First Day Data after the Main Shock?

    NASA Astrophysics Data System (ADS)

    Omi, T.; Ogata, Y.; Hirata, Y.; Aihara, K.

    2014-12-01

    A large earthquake triggers persistent aftershock activity in and near the focal region. Thus, intermediate term forecasting of aftershocks at its earlier stage is important for mitigating seismic risks. A main difficulty for the early forecasting is the substantial incompleteness of early aftershock data. To deal with such incomplete data, we have developed a statistical model of the incomplete data, enabling us to obtain the immediate estimate of the forecasting models from incomplete data [1, 2]. Another difficulty for the intermediate term forecasting is that we have to determine the parameter values of the forecasting models with high accuracy, because even a small bias in the parameter values can lead to a significant bias of the forecasting in intermediate term. However such accurate estimation is quite difficult at the early stage, especially using the early and incomplete data. Here we present a Bayesian forecasting method by using the epidemic-type aftershock sequence (ETAS) model. The Bayesian forecasting considers not only the best parameter values such as the maximum likelihood estimates or maximum a posteriori estimates but also the estimation uncertainty of the parameter values. By analyzing aftershock sequences in Japan, we show the forecasting performances of the intermediate-term aftershocks can be significantly improved by considering the estimation uncertainty of the ETAS model [3]. Furthermore, we discuss the impact of the modeling of the magnitude frequency distribution of detected aftershocks within a day span on the forecasting of large aftershocks. [1] T. Omi, Y. Ogata, Y. Hirata and K. Aihara, "Forecasting large aftershocks within one day after the main shock", Scientific Reports 3, 2218 (2013). [2] T. Omi, Y. Ogata, Y. Hirata and K. Aihara, "Estimating the ETAS model from an early aftershock sequence", Geophysical Research Letters 41, 850 (2014). [3] T. Omi, Y. Ogata, Y. Hirata and K. Aihara, "Intermediate-term forecasting of aftershocks

  4. On the adaptive daily forecasting of seismic aftershock hazard

    NASA Astrophysics Data System (ADS)

    Ebrahimian, Hossein; Jalayer, Fatemeh; Asprone, Domenico; Lombardi, Anna Maria; Marzocchi, Warner; Prota, Andrea; Manfredi, Gaetano

    2013-04-01

    Post-earthquake ground motion hazard assessment is a fundamental initial step towards time-dependent seismic risk assessment for buildings in a post main-shock environment. Therefore, operative forecasting of seismic aftershock hazard forms a viable support basis for decision-making regarding search and rescue, inspection, repair, and re-occupation in a post main-shock environment. Arguably, an adaptive procedure for integrating the aftershock occurrence rate together with suitable ground motion prediction relations is key to Probabilistic Seismic Aftershock Hazard Assessment (PSAHA). In the short-term, the seismic hazard may vary significantly (Jordan et al., 2011), particularly after the occurrence of a high magnitude earthquake. Hence, PSAHA requires a reliable model that is able to track the time evolution of the earthquake occurrence rates together with suitable ground motion prediction relations. This work focuses on providing adaptive daily forecasts of the mean daily rate of exceeding various spectral acceleration values (the aftershock hazard). Two well-established earthquake occurrence models suitable for daily seismicity forecasts associated with the evolution of an aftershock sequence, namely, the modified Omori's aftershock model and the Epidemic Type Aftershock Sequence (ETAS) are adopted. The parameters of the modified Omori model are updated on a daily basis using Bayesian updating and based on the data provided by the ongoing aftershock sequence based on the methodology originally proposed by Jalayer et al. (2011). The Bayesian updating is used also to provide sequence-based parameter estimates for a given ground motion prediction model, i.e. the aftershock events in an ongoing sequence are exploited in order to update in an adaptive manner the parameters of an existing ground motion prediction model. As a numerical example, the mean daily rates of exceeding specific spectral acceleration values are estimated adaptively for the L'Aquila 2009

  5. The Aftershock Sequence of the 2008 Achaia, Greece, Earthquake: Joint Analysis of Seismicity Relocation and Persistent Scatterers Interferometry

    NASA Astrophysics Data System (ADS)

    Karakostas, Vassilis; Mirek, Katarzyna; Mesimeri, Maria; Papadimitriou, Eleftheria; Mirek, Janusz

    2017-01-01

    On 8 June 2008 an earthquake of Mw6.4 took place in the northwestern part of Peloponnese, Greece. The main shock was felt in a wide area and caused appreciable damage along the main rupture area and particularly at the antipodal of the main shock epicenter fault edge, implying strongly unilateral rupture and stopping phase effects. Abundant aftershocks were recorded within an area of 50 km in length in the period 8 June 2008-end of 2014, by a sufficient number of stations that secure location accuracy because the regional network is adequately dense in the area. All the available phases from seismological stations in epicentral distances up to 140 km until the end of 2014 were used for relocation with the double difference technique and waveform cross-correlation. A quite clear 3-D representation is obtained for the aftershock zone geometry and dimensions, revealing the main rupture and the activated adjacent fault segments. SAR data are processed using Stanford Method for Persistent Scatterers (StaMPS) and a surface deformation map constructed based on PS point displacement for the coseismic period. A variable slip model, with maximum slip of 1.0 m located at the lower part of the rupture plane, is suggested and used for calculating the deformation field which was found in adequate agreement with geodetic measurements. With the same slip model the static stress changes were calculated evidencing possible triggering of the neighboring faults that were brought closer to failure. The data availability allowed monitoring the temporal variation of b values that after a continuous increase in the first 5 days, returned and stabilized to 1.0-1.1 in the following years. The fluctuation duration is considered as the equivalent time for fault healing, which appeared very short but in full accordance with the cessation of onto-fault seismicity.

  6. Reduced Aftershock Productivity in Regions with Known Slow Slip Events

    NASA Astrophysics Data System (ADS)

    Collins, G.; Mina, A.; Richardson, E.; McGuire, J. J.

    2013-12-01

    Reduced aftershock activity has been observed in areas with high rates of aseismic slip, such as transform fault zones and some subduction zones. Fault conditions that could explain both of these observations include a low effective normal stress regime and/or a high temperature, semi-brittle/plastic rheology. To further investigate the possible connection between areas of aseismic slip and reduced aftershock productivity, we compared the mainshock-aftershock sequences in subduction zones where aseismic slip transients have been observed to those of adjacent (along-strike) regions where no slow slip events have been detected. Using the Advanced National Seismic System (ANSS) catalog, we counted aftershocks that occurred within 100 km and 14 days of 112 M>=5.0 slab earthquake mainshocks from January 1980 - July 2013, including 90 since January 2000, inside observed regions of detected slow slip: south central Alaska, Cascadia, the Nicoya Peninsula (Costa Rica), Guerrero (Mexico), and the North Island of New Zealand. We also compiled aftershock counts from 97 mainshocks from areas adjacent to each of these regions using the same criteria and over the same time interval. Preliminary analysis of these two datasets shows an aftershock triggering exponent (alpha in the ETAS model) of approximately 0.8, consistent with previous studies of aftershocks in a variety of tectonic settings. Aftershock productivity for both datasets is less than that of continental earthquakes. Contrasting the two datasets, aftershock productivity inside slow slip regions is lower than in adjacent areas along the same subduction zone and is comparable to that of mid-ocean ridge transform faults.

  7. Aftershock distribution as a constraint on the geodetic model of coseismic slip for the 2004 Parkfield earthquake

    USGS Publications Warehouse

    Bennington, Ninfa; Thurber, Clifford; Feigl, Kurt; ,

    2011-01-01

    Several studies of the 2004 Parkfield earthquake have linked the spatial distribution of the event’s aftershocks to the mainshock slip distribution on the fault. Using geodetic data, we find a model of coseismic slip for the 2004 Parkfield earthquake with the constraint that the edges of coseismic slip patches align with aftershocks. The constraint is applied by encouraging the curvature of coseismic slip in each model cell to be equal to the negative of the curvature of seismicity density. The large patch of peak slip about 15 km northwest of the 2004 hypocenter found in the curvature-constrained model is in good agreement in location and amplitude with previous geodetic studies and the majority of strong motion studies. The curvature-constrained solution shows slip primarily between aftershock “streaks” with the continuation of moderate levels of slip to the southeast. These observations are in good agreement with strong motion studies, but inconsistent with the majority of published geodetic slip models. Southeast of the 2004 hypocenter, a patch of peak slip observed in strong motion studies is absent from our curvature-constrained model, but the available GPS data do not resolve slip in this region. We conclude that the geodetic slip model constrained by the aftershock distribution fits the geodetic data quite well and that inconsistencies between models derived from seismic and geodetic data can be attributed largely to resolution issues.

  8. Typical Scenario of Preparation, Implementation, and Aftershock Sequence of a Large Earthquake

    NASA Astrophysics Data System (ADS)

    Rodkin, Mikhail

    2016-04-01

    We have tried here to construct and examine the typical scenario of a large earthquake occurrence. The Harvard seismic moment GCMT catalog was used to construct the large earthquake generalized space-time vicinity (LEGV) and to investigate the seismicity behavior in LEGV. LEGV was composed of earthquakes falling into the zone of influence of any of the considerable number (100, 300, or 1,000) of largest earthquakes. The LEGV construction is aimed to enlarge the available statistics, diminish a strong random component, and to reveal in result the typical features of pre- and post-shock seismic activity in more detail. In result of the LEGV construction the character of fore- and aftershock cascades was examined in more detail than it was possible without of the use of the LEGV approach. It was shown also that the mean earthquake magnitude tends to increase, and the b-values, mean mb/mw ratios, apparent stress values, and mean depth tend to decrease. Amplitudes of all these anomalies increase with an approach to a moment of the generalized large earthquake (GLE) as a logarithm of time interval from GLE occurrence. Most of the discussed anomalies agree well with a common scenario of development of instability. Besides of such precursors of common character, one earthquake-specific precursor was found. The revealed decrease of mean earthquake depth during large earthquake preparation testifies probably for the deep fluid involvement in the process. The revealed in LEGV typical features of development of shear instability agree well with results obtained in laboratory acoustic emission (AE) study. Majority of the revealed anomalies appear to have a secondary character and are connected mainly with an increase in a mean earthquake magnitude in LEGV. The mean magnitude increase was shown to be connected mainly with a decrease of a portion of moderate size events (Mw 5.0 - 5.5) in a closer GLE vicinity. We believe that this deficit of moderate size events hardly can be

  9. April 25, 2015, Gorkha Earthquake, Nepal and Sequence of Aftershocks: Key Lessons

    NASA Astrophysics Data System (ADS)

    Guragain, R.; Dixit, A. M.; Shrestha, S. N.

    2015-12-01

    The Gorkha Earthquake of M7.8 hit Nepal on April 25, 2015 at 11:56 am local time. The epicenter of this earthquake was Barpak, Gorkha, 80 km northwest of Kathmandu Valley. The main shock was followed by hundreds of aftershocks including M6.6 and M6.7 within 48 hours and M7.3 on May 12, 2015. According to the Government of Nepal, a total of 8,686 people lost their lives, 16,808 people injured, over 500,000 buildings completely collapsed and more than 250,000 building partially damaged. The National Society for Earthquake Technology - Nepal (NSET), a not-for-profit civil society organization that has been focused on earthquake risk reduction in Nepal for past 21 years, conducted various activities to support people and the government in responding to the earthquake disaster. The activities included: i) assisting people and critical facility institutions to conduct rapid visual building damage assessment including the training; ii) information campaign to provide proper information regarding earthquake safety; iii) support rescue organizations on search and rescue operations; and iv) provide technical support to common people on repair, retrofit of damaged houses. NSET is also involved in carrying out studies related to earthquake damage, geotechnical problems, and causes of building damages. Additionally, NSET has done post-earthquake detail damage assessment of buildings throughout the affected areas. Prior to the earthquake, NSET has been working with several institutions to improve seismic performance of school buildings, private residential houses, and other critical structures. Such activities implemented during the past decade have shown the effectiveness of risk reduction. Retrofitted school buildings performed very well during the earthquake. Preparedness activities implemented at community levels have helped communities to respond immediately and save lives. Higher level of earthquake awareness achieved including safe behavior, better understanding of

  10. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  11. When and where the aftershock activity was depressed: Contrasting decay patterns of the proximate large earthquakes in southern California

    USGS Publications Warehouse

    Ogata, Y.; Jones, L.M.; Toda, S.

    2003-01-01

    Seismic quiescence has attracted attention as a possible precursor to a large earthquake. However, sensitive detection of quiescence requires accurate modeling of normal aftershock activity. We apply the epidemic-type aftershock sequence (ETAS) model that is a natural extension of the modified Omori formula for aftershock decay, allowing further clusters (secondary aftershocks) within an aftershock sequence. The Hector Mine aftershock activity has been normal, relative to the decay predicted by the ETAS model during the 14 months of available data. In contrast, although the aftershock sequence of the 1992 Landers earthquake (M = 7.3), including the 1992 Big Bear earthquake (M = 6.4) and its aftershocks, fits very well to the ETAS up until about 6 months after the main shock, the activity showed clear lowering relative to the modeled rate (relative quiescence) and lasted nearly 7 years, leading up to the Hector Mine earthquake (M = 7.1) in 1999. Specifically, the relative quiescence occurred only in the shallow aftershock activity, down to depths of 5-6 km. The sequence of deeper events showed clear, normal aftershock activity well fitted to the ETAS throughout the whole period. We argue several physical explanations for these results. Among them, we strongly suspect aseismic slips within the Hector Mine rupture source that could inhibit the crustal relaxation process within "shadow zones" of the Coulomb's failure stress change. Furthermore, the aftershock activity of the 1992 Joshua Tree earthquake (M = 6.1) sharply lowered in the same day of the main shock, which can be explained by a similar scenario.

  12. A non-extensive statistical physics view to the spatiotemporal properties of the June 1995, Aigion earthquake (M6.2) aftershock sequence (West Corinth rift, Greece)

    NASA Astrophysics Data System (ADS)

    Vallianatos, Filippos; Michas, Giorgos; Papadakis, Giorgos; Sammonds, Peter

    2012-06-01

    In the present study, the spatiotemporal properties of the Aigion earthquake (15 June 1995) aftershock sequence are being studied using the concept of non-extensive statistical physics (NESP). The cumulative distribution functions of the inter-event times and the inter-event distances are being estimated for the data set which is assumed to be complete and the analysis yielded the thermodynamic q parameter to be qT = 1.58 and q r = 0.53 for the two distributions, respectively. The results fit rather well to the inter-event distances and times distributions, implying the complexity of the spatiotemporal properties of seismicity and the usefulness of NESP in investigating such phenomena. The temporal structure is also being discussed using the complementary to NESP approach of superstatistics, which is based on a superposition of ordinary local equilibrium statistical mechanics. The result indicates that very low degrees of freedom describe the temporal evolution of the Aigion earthquake aftershock seismicity.

  13. Preliminary report on aftershock sequence for earthquake of January 31, 1986, near Painesville, Ohio (time period: 2/1/86-2/10/86)

    USGS Publications Warehouse

    Borcherdt, R. D.

    1986-01-01

    A ten-station array of broad-band digital instrumentation (GEOS) was deployed by the U. S. Geological Survey with partial support provided by Electric Power Research Institute to record the aftershock sequence of the moderate (mb ~ 4.9) earthquake that occurred on January 31, 1986 (16:46:43 UTC) near Painesville, Ohio. The occurrence of the event has raised questions concerning possible contributory factors to the occurrence of the event and questions concerning the character of earthquake-induced high-frequency ground motions in the area. To aid in the timely resolution of the implications of some of these questions, this preliminary report provides copies of the ground motion time-histories and corresponding spectra for the six identified aftershocks and two events, thought to be quarry blasts, recorded as of February 10, 1986. Recording station locations and epicenter locations based on two preliminary estimates of local seismic velocity structure are provided.

  14. What Controls the Duration of Aftershocks, and Why It Matters for Probabilistic Seismic Hazard Assessment

    NASA Astrophysics Data System (ADS)

    Stein, R. S.; Toda, S.

    2014-12-01

    A fundamental problem confronting hazard modelers in slowly deforming regions such as the central and eastern United States, Australia, and inner Honshu, is whether the current seismicity represents the steady state earthquake potential, or is instead a decaying potential associated with past mainshocks. If the current seismicity were composed of long-lived aftershock sequences, it might then be anti-correlated with the next large earthquakes. While aftershock productivity is known to be a property of the mainshock magnitude, aftershock duration (the time until the aftershock rate decays to the pre-mainshock rate) should, according to rate/state friction theory of Dieterich[1994], be inversely proportional to the fault stressing rate. If so, slowly deforming regions would be expected to sustain long aftershock sequences. Most tests have supported the Dieterich hypothesis, but use ambiguous proxies for the fault stressing rate, such as the mainshock recurrence interval. Here we test the hypothesis by examining off-fault aftershocks of the 2011 M=9 Tohoku-oki rupture up to 250 km from the source, as well as near-fault aftershocks of six large Japanese mainshocks, sampling a range of receiver faults, from thrusts slipping 80 mm/yr, to normal faults slipping 0.1 mm/yr. We find that aftershock sequences lasted a month on the fastest-slipping faults, have durations of 10-100 years on faults slipping 1-10 mm/yr, and are projected to persist for at least 200 years on the slowest faults. Although the Omori decay exponent for short and long sequences is similar, the very different background rates account for the duration differences. If the stressing rate is generally proportional to fault slip rate, then aftershock durations indeed support the Dieterich hypothesis. The test means that the hazard associated with aftershocks depends on local tectonic conditions rather than on the mainshock magnitude alone. Because declustering approaches do not remove such long

  15. Estimating Spatially Variable Parameters of the Epidemic Type Aftershock Sequence (ETAS) in California

    NASA Astrophysics Data System (ADS)

    Nandan, Shyam; Ouillon, Guy; Sornette, Didier; Wiemer, Stefan

    2016-04-01

    The ETAS model is widely employed to model the spatio-temporal distribution of earthquakes, generally using spatially invariant parameters, which is most likely a gross simplification considering the extremely heterogeneous structure of the Earth's crust. We propose an efficient method for the estimation of spatially varying parameters, using an expectation maximization (EM) algorithm and spatial Voronoi tessellations. We assume that each Voronoi cell is characterized by a set of eight constant ETAS parameters. For a given number of randomly distributed cells, Vi=1 to N, we jointly invert the ETAS parameters within each cell using an EM algorithm. This process is progressively repeated several times for a given N (which controls the complexity), which is itself increased incrementally. We use the Bayesian Information Criterion (BIC) to rank all the inverted models given their likelihood and complexity and select the top 1% models to compute the average model at any location. Using a synthetic catalog, we also check that the proposed method correctly inverts the known parameters. We apply the proposed method to earthquakes (M>=3) included in the ANSS catalog that occurred within the time period 1981-2016 in the spatial polygon defined by RELM/CSEP around California. The results indicate significant spatial variation of the ETAS parameters. Using these spatially variable estimates of ETAS parameters, we are better equipped to answer some important questions: (1) What is the seismic hazard (both long- and short-term) in a given region? (2) What kind of earthquakes dominate triggering? (3) are there regions where earthquakes are most likely preceded by foreshocks? Last but not the least, a possible correlation of the spatially varying ETAS parameters with spatially variable geophysical properties can lead to an improved understanding of the physics of earthquake triggering beside providing physical meaning to the parameters of the purely statistical ETAS model.

  16. The M w6.7 12 October 2013 western Hellenic Arc main shock and its aftershock sequence: implications for the slab properties

    NASA Astrophysics Data System (ADS)

    Papadimitriou, Eleftheria; Karakostas, Vassilis; Mesimeri, Maria; Vallianatos, Filippos

    2016-10-01

    The 12 October 2013 M w6.7 earthquake offshore Crete Island is one of the few strong earthquakes to have occurred in the last few decades in the southwestern part of the Hellenic subduction zone (HSZ), providing the opportunity to evaluate characteristics of the descending slab. The HSZ has experienced several strong ( M ≥ 7.0) earthquakes in historical times with the largest one being the 365 AD, M w = 8.4 earthquake, the largest known ever occurred in the Mediterranean region. The 2013 main shock occurred in close proximity with the 365 event, on an interplate thrust fault at a depth of 26 km, onto the coupled part of the overriding and descending plates. GCMT solution shows a slightly oblique (rake = 130°) thrust faulting with downdip compression on a nearly horizontal (dip = 3°) northeast-dipping fault plane with strike (340°) parallel to the subduction front, with the compression axis being oriented in the direction of plate convergence. The subduction interface can be more clearly resolved with the integration of aftershock locations and CMT solution. For this scope, the aftershocks were relocated after obtaining a v p/ v s ratio equal to 1.76, a one-dimensional velocity model and time delays that approximate the velocity structure of the study area, and the employment of double-difference technique for both phase pick data and cross-correlation differential times. The first-day relocated seismicity, alike aftershocks in the first 2 months, shows activation of an area at the upper part of the descending slab, with most activity being concentrated between 13 and 27 km, where the main shock is also encompassed. Aftershocks are rare near to the main shock, implying homogeneous slip on a large patch of the rupture plane. Based on the aftershock distribution, the size of the activated area estimated is about 24 km long and 17 km wide. Coulomb stress changes resolved for transpressive motion reveal negligible off-fault aftershock triggering, evidencing a

  17. Aftershock Decay Rates in the Iranian Plateau

    NASA Astrophysics Data System (ADS)

    Ommi, S.; Zafarani, H.; Zare, M.

    2016-07-01

    Motivated by the desire to have more information following the occurrence of damaging events, the main purpose of this article is to study aftershock sequence parameters in the Iranian plateau. To this end, the catalogue of the Iranian earthquakes between 2002 to the end of 2013 has been collected and homogenized among which 15 earthquakes have been selected to study their aftershock decay rates. For different tectonic provinces, the completeness magnitudes ( M c) of the earthquake catalogue have been calculated in different time intervals. Also, the M c variability in spatial and temporal windows has been determined for each selected event. For major Iranian earthquakes, catalogue of aftershocks has been collected thanks to three declustering methods: first, the classical windowing method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974); second, a modified version of this using spatial windowing based on the Wells and Coppersmith (Bull Seismol Soc Am 84:974-1002, 1994) relations; and third, the Burkhard and Grünthal (Swiss J Geosci 102:149-188, 2009) scheme. Effects of the temporal windows also have been investigated using the time periods of 1 month, 100 days, and 1 year in the declustering method of Gardner and Knopoff (Bull Seismol Soc Am 64:1363-1367, 1974). In the next step, the modified Omori law coefficients have been calculated for the 15 selected earthquakes. The calibrated regional generic model describing the temporal and magnitude distribution of aftershocks is of interest for time-dependent seismic hazard forecasts. The regional characteristics of the aftershock decay rates have been studied for the selected Iranian earthquakes in the Alborz, Zagros and Central Iran regions considering their different seismotectonics regimes. However, due to the lack of sufficient data, no results have been reported for the Kopeh-Dagh and Makran seismotectonic regions.

  18. Source parameters of the Mw = 6.3 Aroma crustal earthquake of July 24, 2001 (northern Chile), and its aftershock sequence

    NASA Astrophysics Data System (ADS)

    Legrand, D.; Delouis, B.; Dorbath, L.; David, C.; Campos, J.; Marquéz, L.; Thompson, J.; Comte, D.

    2007-06-01

    The July 24, 2001, Mw = 6.3 earthquake in Aroma, Chile, is one of the few moderately shallow earthquakes to occur recently in northern Chile. This study uses different seismological data (short-period, broadband, strong-motion) to locate the event and its corresponding aftershocks. In addition, it carefully constrains the focal depth using SP phase and the focal mechanism of the main-shock. Finally, a model of the strong-motion waveforms discriminates the activated fault plane among the two nodal planes. The main-shock fault plane solution obtained from the strong-motion analysis is (strike, dip, rake) = (14° ± 10°, 53° ± 15°, -163° ± 15°), which indicates a right-lateral motion on an inclined fault, in agreement with the aftershock distribution, which also indicates a fault striking N14°E and dipping about 50°E.

  19. Source Process of the Mw 5.0 Au Sable Forks, New York, Earthquake Sequence from Local Aftershock Monitoring Network Data

    NASA Astrophysics Data System (ADS)

    Kim, W.; Seeber, L.; Armbruster, J. G.

    2002-12-01

    On April 20, 2002, a Mw 5 earthquake occurred near the town of Au Sable Forks, northeastern Adirondacks, New York. The quake caused moderate damage (MMI VII) around the epicentral area and it is well recorded by over 50 broadband stations in the distance ranges of 70 to 2000 km in the Eastern North America. Regional broadband waveform data are used to determine source mechanism and focal depth using moment tensor inversion technique. Source mechanism indicates predominantly thrust faulting along 45° dipping fault plane striking due South. The mainshock is followed by at least three strong aftershocks with local magnitude (ML) greater than 3 and about 70 aftershocks are detected and located in the first three months by a 12-station portable seismographic network. The aftershock distribution clearly delineate the mainshock rupture to the westerly dipping fault plane at a depth of 11 to 12 km. Preliminary analysis of the aftershock waveform data indicates that orientation of the P-axis rotated 90° from that of the mainshock, suggesting a complex source process of the earthquake sequence. We achieved an important milestone in monitoring earthquakes and evaluating their hazards through rapid cross-border (Canada-US) and cross-regional (Central US-Northeastern US) collaborative efforts. Hence, staff at Instrument Software Technology, Inc. near the epicentral area joined Lamont-Doherty staff and deployed the first portable station in the epicentral area; CERI dispatched two of their technical staff to the epicentral area with four accelerometers and a broadband seismograph; the IRIS/PASSCAL facility shipped three digital seismographs and ancillary equipment within one day of the request; the POLARIS Consortium, Canada sent a field crew of three with a near real-time, satellite telemetry based earthquake monitoring system. The Polaris station, KSVO, powered by a solar panel and batteries, was already transmitting data to the central Hub in London, Ontario, Canada within

  20. Evidence that Stress Amplitude Does Not Affect the Temporal Distribution of Aftershocks

    NASA Astrophysics Data System (ADS)

    Felzer, K. R.

    2005-12-01

    Most physical aftershock triggering models, including the rate and state friction model of Dieterich (1994), the stress corrosion model (see discussion in Gomberg, 2001) and other accelerating failure models predict that larger stress changes on a fault will lead to an aftershocks that happens more quickly (larger clock advance), all else equal. Thus as stress change amplitude decreases with distance from the mainshock, there is an expected shift in the aftershock distribution toward longer time delays. This effect was formalized by Dieterich (1994) as an increase of the modified Omori Law c value (N(t) = A/(t+c)p where t = time, N(t) = aftershock rate, and A, p, and c are constants). Jones and Hauksson (1998), however, found no change in c value with distance after the 1992 MW 7.3 Landers earthquake. The assumption that the aftershock temporal distribution is independent of distance is also made in ETAS (Epidemic Triggering Aftershock Sequence) aftershock simulations (Ogata, 1998; Helmstetter, 2002) without adverse affect on fitting real data. Here we verify the independence of stress change and aftershock temporal distribution using a data set of 33 M 5-6 mainshocks from throughout California. These mainshocks are large enough to produce a significant number of aftershocks in the near and far field, but small enough to be frequent and thus provide good statistical sampling. Our data verifies that the temporal distribution of aftershocks is independent of stress change amplitude. We suggest that the most likely explanation for this observation is that the timing of each fault that participates in an aftershock sequence is independent of the amplitude of the stress that triggers it. In this case aftershock decay with distance from the mainshock cannot be caused by smaller clock advances on lesser-stressed faults, as in the Dieterich (1994) model, but rather by a stress amplitude dependent probability that a fault will be clock advanced at all. In future work we

  1. The LVD signals during the early-mid stages of the L'Aquila seismic sequence and the radon signature of some aftershocks of moderate magnitude.

    PubMed

    Cigolini, C; Laiolo, M; Coppola, D

    2015-01-01

    The L'Aquila seismic swarm culminated with the mainshock of April 6, 2009 (ML = 5.9). Here, we report and analyze the Large Volume Detector (LVD, used in neutrinos research) low energy traces (∼0.8 MeV), collected during the early-mid stages of the seismic sequence, together with the data of a radon monitoring experiment. The peaks of LVD traces do not correlate with the evolution and magnitude of earthquakes, including major aftershocks. Conversely, our radon measurements obtained by utilizing three automatic stations deployed along the regional NW-SE faulting system, seem to be, in one case, more efficient. In fact, the timeseries collected on the NW-SE Paganica fracture recorded marked variations and peaks that occurred during and prior moderate aftershocks (with ML > 3). The Paganica monitoring station (PGN) seems to better responds to active seismicity due to the fact that the radon detector was placed directly within the bedrock of an active fault. It is suggested that future networks for radon monitoring of active seismicity should preferentially implement this setting.

  2. Nonlinear Viscoelastic Stress Transfer As a Possible Aftershock Triggering Mechanism

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Shcherbakov, R.

    2014-12-01

    The earthquake dynamics can be modelled by employing the spring-block system [Burridge and Knopoff, 1967]. In this approach the earthquake fault is modelled by an array of blocks coupling the loading plate and the lower plate. The dynamics of the system is governed by the system of equations of motion for each block. It is possible to map this system into a cellular automata model, where the stress acting on each block is increased in each time step, and the failing process (frictional slip) is described by stress transfer rules [Olami et al, 1992]. The OFC model produces a power-law distribution for avalanche statistics but it is not capable of producing robust aftershock sequences which follow Omori's law.We propose a nonlinear viscoelastic stress transfer mechanism in the aftershock triggering. In a basic spring-block model setting, we introduce the nonlinear viscoelastic stress transfer between neighbouring blocks, as well as between blocks and the top loading plate. The shear stress of the viscous component is a power-law function of the velocity gradient with an exponent smaller or greater than 1 for the nonlinear viscoelasticity, or 1 for the linear case. The stress transfer function of this nonlinear viscoelastic model has a power-law time-dependent form. It features an instantaneous stress transmission triggering an instantaneous avalanche, which is the same as the original spring-block model; and a power-law relaxation term, which could trigger further aftershocks. We incorporate this nonlinear viscoelasticity mechanism in a lattice cellular automata model. The model could exhibit both the Gutenberg-Richter scaling for the frequency-magnitude distribution and a power-law time decay of aftershocks, which is in accordance with Omori's law. Our study suggests that the stress transfer function may play an important role in the aftershock triggering. We have found that the time decay curve of aftershocks is affected by the shape of the stress transfer function

  3. The Importance of Small Aftershocks for Earthquake Triggering

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Meier, M.; Werner, M. J.; Wiemer, S.

    2011-12-01

    The thousands of aftershocks after large earthquakes illustrate how the stress state of the lithosphere is regionally altered during large events. To date, however, the exact physical mechanism for this triggering remains unclear. A popular and intuitive model is Coulomb stress change theory, which quantifies how the static stress changes induced by nearby earthquakes alter the likelihood of brittle failure on potential aftershock fault planes. Several assumptions are made to facilitate the calculation of stress changes; here, we challenge the typical neglect of the stress changes induced by the small but numerous and strongly clustered aftershocks during the evolution of the sequence. Both empirical observations and a simple scaling law suggest that this neglect may not be justified. In this study, we estimate the evolution of Coulomb stress changes during the 1992 Mw 7.3 Landers earthquake sequence by including the effect of the detected aftershocks with available focal mechanisms. Our calculations suggest that the small events strongly dominate static stress redistribution in isolated secondary aftershock clusters. However, their relative importance strongly varies over space and is, on average, smaller than the mainshock's. Nonetheless, neglecting the cumulative effect of small earthquakes can locally substantially alter the estimated stress change. We also find that the overall percentage of aftershocks in agreement with Coulomb triggering decreases upon the inclusion of the small events. However, the uncertainties in stress change calculations are even larger for small earthquakes than for a mainshock: focal mechanisms are incomplete and poorly constrained; a fault plane must be inferred; slips needs to be estimated from local magnitude; etc. To examine the role of the uncertainties in the available focal mechanisms, we generate perturbed catalogs based on estimated focal mechanism uncertainties and attempt to quantify their significance for the Coulomb

  4. Aftershocks and triggered events of the Great 1906 California earthquake

    USGS Publications Warehouse

    Meltzner, A.J.; Wald, D.J.

    2003-01-01

    and an M ???5.0 event under or near Santa Monica Bay, 11.3 and 31.3 hr after the San Francisco mainshock, respectively. The western Arizona event is inferred to have been triggered dynamically. In general, the largest aftershocks occurred at the ends of the 1906 rupture or away from the rupture entirely; very few significant aftershocks occurred along the mainshock rupture itself. The total number of large aftershocks was less than predicted by a generic model based on typical California mainshock-aftershock statistics, and the 1906 sequence appears to have decayed more slowly than average California sequences. Similarities can be drawn between the 1906 aftershock sequence and that of the 1857 (Mw 7.9) San Andreas fault earthquake.

  5. International Aftershock Forecasting: Lessons from the Gorkha Earthquake

    NASA Astrophysics Data System (ADS)

    Michael, A. J.; Blanpied, M. L.; Brady, S. R.; van der Elst, N.; Hardebeck, J.; Mayberry, G. C.; Page, M. T.; Smoczyk, G. M.; Wein, A. M.

    2015-12-01

    Following the M7.8 Gorhka, Nepal, earthquake of April 25, 2015 the USGS issued a series of aftershock forecasts. The initial impetus for these forecasts was a request from the USAID Office of US Foreign Disaster Assistance to support their Disaster Assistance Response Team (DART) which coordinated US Government disaster response, including search and rescue, with the Government of Nepal. Because of the possible utility of the forecasts to people in the region and other response teams, the USGS released these forecasts publicly through the USGS Earthquake Program web site. The initial forecast used the Reasenberg and Jones (Science, 1989) model with generic parameters developed for active deep continental regions based on the Garcia et al. (BSSA, 2012) tectonic regionalization. These were then updated to reflect a lower productivity and higher decay rate based on the observed aftershocks, although relying on teleseismic observations, with a high magnitude-of-completeness, limited the amount of data. After the 12 May M7.3 aftershock, the forecasts used an Epidemic Type Aftershock Sequence model to better characterize the multiple sources of earthquake clustering. This model provided better estimates of aftershock uncertainty. These forecast messages were crafted based on lessons learned from the Christchurch earthquake along with input from the U.S. Embassy staff in Kathmandu. Challenges included how to balance simple messaging with forecasts over a variety of time periods (week, month, and year), whether to characterize probabilities with words such as those suggested by the IPCC (IPCC, 2010), how to word the messages in a way that would translate accurately into Nepali and not alarm the public, and how to present the probabilities of unlikely but possible large and potentially damaging aftershocks, such as the M7.3 event, which had an estimated probability of only 1-in-200 for the week in which it occurred.

  6. Rupture Processes of the Mw8.3 Sea of Okhotsk Earthquake and Aftershock Sequences from 3-D Back Projection Imaging

    NASA Astrophysics Data System (ADS)

    Jian, P. R.; Hung, S. H.; Meng, L.

    2014-12-01

    On May 24, 2013, the largest deep earthquake ever recorded in history occurred on the southern tip of the Kamchatka Island, where the Pacific Plate subducts underneath the Okhotsk Plate. Previous 2D beamforming back projection (BP) of P- coda waves suggests the mainshock ruptured bilaterally along a horizontal fault plane determined by the global centroid moment tensor solution. On the other hand, the multiple point source inversion of P and SH waveforms argued that the earthquake comprises a sequence of 6 subevents not located on a single plane but actually distributed in a zone that extends 64 km horizontally and 35 km in depth. We then apply a three-dimensional MUSIC BP approach to resolve the rupture processes of the manishock and two large aftershocks (M6.7) with no a priori setup of preferential orientations of the planar rupture. The maximum pseudo-spectrum of high-frequency P wave in a sequence of time windows recorded by the densely-distributed stations from US and EU Array are used to image 3-D temporal and spatial rupture distribution. The resulting image confirms that the nearly N-S striking but two antiparallel rupture stages. The first subhorizontal rupture initially propagates toward the NNE direction, while at 18 s later it directs reversely to the SSW and concurrently shifts downward to 35 km deeper lasting for about 20 s. The rupture lengths in the first NNE-ward and second SSW-ward stage are about 30 km and 85 km; the estimated rupture velocities are 3 km/s and 4.25 km/s, respectively. Synthetic experiments are undertaken to assess the capability of the 3D MUSIC BP for the recovery of spatio-temporal rupture processes. Besides, high frequency BP images based on the EU-Array data show two M6.7 aftershocks are more likely to rupture on the vertical fault planes.

  7. Quantitative Mapping of Precursory Seismic Quiescence Before Large Aftershocks

    NASA Astrophysics Data System (ADS)

    Neukomm, S.; Wiemer, S.; Giardini, D.

    2002-12-01

    A relative decrease of aftershock activity before the occurrence of large aftershocks to M6+ mainshocks is one of only few earthquake precursors accepted for the IASPEI preliminary list of significant earthquake precursors. If one considers earthquake rate to be dependent on stressing rate, aftershocks sequences offer in fact an ideal environment to detect precursory quiescence before large earthquakes: The numerous aftershocks allow a much higher spatial and temporal resolution of transients in seismicity than possible with the average background rate of micro-earthquakes. Past studies of precursory quiescence before larger aftershocks, however, have largely been based on bulk value. The aim of this study is to map the temporal and spatial variability of activity rate within several rich aftershock sequences, and, possibly, exploit the results for improving real time probabilistic aftershock hazard assessment. We introduce a new algorithm based on fitting the modified Omori law to the aftershock sequences. At arbitrarily chosen grid points, the Omori parameters of the sub-samples containing all aftershock within 5 or 10 km of the node are estimated at time t. We calculate the number of aftershocks N +/- dN in the time interval t + dt using the relevant four Omori parameters (p, c and k) parameters and their corresponding standard deviations estimated using a bootstrap analysis. The difference between the forecasted and the observed number of aftershocks, normalized by the standard deviation of the forecast, is our estimator of rate change. The algorithm is tested on synthetic aftershock sequences containing artificial quiescences in order to calibrate the free parameters for optimal detection of precursory quiescence. We then perform our spatial and temporal mapping for several prominent Californian and Japanese aftershock sequences (Landers, Hector Mine, Northridge, Loma Prieta, Kobe, Western Tottori and Hokkaido). Preliminary results suggest that we cannot

  8. Analysing the 1811-1812 New Madrid earthquakes with recent instrumentally recorded aftershocks

    USGS Publications Warehouse

    Mueller, K.; Hough, S.E.; Bilham, R.

    2004-01-01

    Although dynamic stress changes associated with the passage of seismic waves are thought to trigger earthquakes at great distances, more than 60 per cent of all aftershocks appear to be triggered by static stress changes within two rupture lengths of a mainshock. The observed distribution of aftershocks may thus be used to infer details of mainshock rupture geometry. Aftershocks following large mid-continental earthquakes, where background stressing rates are low, are known to persist for centuries, and models based on rate-and-state friction laws provide theoretical support for this inference. Most past studies of the New Madrid earthquake sequence have indeed assumed ongoing microseismicity to be a continuing aftershock sequence. Here we use instrumentally recorded aftershock locations and models of elastic stress change to develop a kinematically consistent rupture scenario for three of the four largest earthquakes of the 1811-1812 New Madrid sequence. Our results suggest that these three events occurred on two contiguous faults, producing lobes of increased stress near fault intersections and end points, in areas where present-day microearthquakes have been hitherto interpreted as evidence of primary mainshock rupture. We infer that the remaining New Madrid mainshock may have occurred more than 200 km north of this region in the Wabash Valley of southern Indiana and Illinois-an area that contains abundant modern microseismicity, and where substantial liquefaction was documented by historic accounts. Our results suggest that future large midplate earthquake sequences may extend over a much broader region than previously suspected.

  9. Forecasting aftershock activity: 1. Adaptive estimates based on the Omori and Gutenberg-Richter laws

    NASA Astrophysics Data System (ADS)

    Baranov, S. V.; Shebalin, P. N.

    2016-05-01

    The method for forecasting the intensity of the aftershock processes after strong earthquakes in different magnitude intervals is considered. The method is based on the joint use of the time model of the aftershock process and the Gutenberg-Richter law. The time model serves for estimating the intensity of the aftershock flow with a magnitude larger than or equal to the magnitude of completeness. The Gutenberg-Richter law is used for magnitude scaling. The suggested approach implements successive refinement of the parameters of both components of the method, which is the main novelty distinguishing it from the previous ones. This approach, to a significant extent, takes into account the variations in the parameters of the frequency-magnitude distribution, which often show themselves by the decreasing fraction of stronger aftershocks with time. Testing the method on eight aftershock sequences in the regions with different patterns of seismicity demonstrates the high probability of successful forecasts. The suggested technique can be employed in seismological monitoring centers for forecasting the aftershock activity of a strong earthquake based on the results of operational processing.

  10. Nontrivial decay of aftershock density with distance in Southern California

    NASA Astrophysics Data System (ADS)

    Moradpour, Javad; Hainzl, Sebastian; Davidsen, Jörn

    2014-07-01

    The decay of the aftershock density with distance plays an important role in the discussion of the dominant underlying cause of earthquake triggering. Here, we provide evidence that its form is more complicated than typically assumed and that in particular a transition in the power law decay occurs at length scales comparable to the thickness of the crust. This is supported by an analysis of a very recent high-resolution catalog for Southern California (SC) and surrogate catalogs generated by the Epidemic-Type Aftershock Sequence (ETAS) model, which take into account inhomogeneous background activity, short-term aftershock incompleteness, anisotropic triggering, and variations in the observational magnitude threshold. Our findings indicate specifically that the asymptotic decay in the aftershock density with distance is characterized by an exponent larger than 2, which is much bigger than the observed exponent of approximately 1.35 observed for shorter distances ranging from the main shock rupture length up to a length scale comparable to the thickness of the crust. This has also important consequences for time-dependent seismic hazard assessment based on the ETAS model.

  11. Evidence Against the New Madrid Long-Lived Aftershock Hypothesis

    NASA Astrophysics Data System (ADS)

    Page, M. T.; Hough, S. E.

    2014-12-01

    It has been suggested that continuing seismicity in the New Madrid, central U.S. region is primarily composed of the continuing long-lived aftershock sequence of the 1811-1812 sequence, and thus cannot be taken as an indication of present-day strain accrual in the region. We examine historical and instrumental seismicity in the New Madrid region to determine if such a model is feasible given 1) the observed protracted nature of past New Madrid sequences, with multiple mainshocks with apparently similar magnitudes; 2) historical rates of M≥6 earthquakes after the initial activity in 1811-1812; and 3) the modern seismicity rate in the region. We use ETAS modeling to search for sub-critical sets of direct Omori parameters that are consistent with all of these datasets, given a realistic consideration of their uncertainties. High aftershock productivity is required both to match the observation of multiple mainshocks and to explain the modern level of activity as aftershocks; synthetic sequences consistent with these observations substantially overpredict the number of events of M≥6 that were observed in the past 200 years. Our results imply that ongoing background seismicity in the New Madrid region is driven by ongoing strain accrual processes and that, despite low deformation rates, seismic activity in the zone is not decaying with time.

  12. The 2010 Haiti earthquake sequence: new insight of the tectonic pattern from aftershocks and marine geophysical data : Haiti-OBS cruise

    NASA Astrophysics Data System (ADS)

    Mercier de Lepinay, B. F.; Mazabraud, Y.; Klingelhoefer, F.; Clouard, V.; Hello, Y.; Graindorge, D.; Marcaillou, B.; Crozon, J.; Saurel, J.; Charvis, P.; Mildor, B. S.; Deschamps, A.; Bouin, M.; Perrot, J.

    2010-12-01

    The devastating 2010 Haiti earthquake ruptured only a relatively short segment (~50km) of the Enriquillo-Plantain Garden fault (EPGF) a 600km long strike-slip fault running onland and offshore from Jamaica to Dominican Republic, with apparently no major surface rupture in the epicentral area. Considering the general behavior of such strike-slip fault (i.e. North Anatolian fault, San Andreas fault), we can expect that, following the 2010 earthquake, other large earthquakes will occur in the near future on adjacent segments. To contribute to the multinational scientific effort for a better understanding of the rupture process and the stress relaxation of this earthquake, we organized the Haiti-OBS cruise of the R/V L'Atalante few weeks after the catastrophe (Feb.5 to Feb.15, 2010, from and to Pointe-a-Pitre, Guadeloupe). Our goal was 1) to deploy a temporary network of seismologic stations -21 OBS, Ocean Bottom Seismometer, and 4 onland stations- and 2) to survey the detailed sea-floor features in relation with the deformation pattern of the area (multibeam bathymetry and mud-penetrator). We show that the distribution pattern of the aftershocks as well as the compressive surface structures observed in the geology and onshore/offshore morphology of the area are consistent with a deformation model implying a major left-lateral component along the EPGF, and a strong reverse component. The January 12, 2010 mainshock has been shown as very complex. However, in the first order, the mainshock and the distribution of the aftershocks, better localized by our temporary network, can be explained by the interaction between the strike-slip EPGF system and a blind folds-and-thrusts system. Thus, the general geological setting shows a southern extension until the southern part of the Canal du Sud area of the well-known fold and thrust system of the Hispaniola main block.

  13. Mechanical origin of aftershocks

    PubMed Central

    Lippiello, E.; Giacco, F.; Marzocchi, W.; Godano, C.; de Arcangelis, L.

    2015-01-01

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering. PMID:26497720

  14. Mechanical origin of aftershocks.

    PubMed

    Lippiello, E; Giacco, F; Marzocchi, W; Godano, C; de Arcangelis, L

    2015-10-26

    Aftershocks are the most striking evidence of earthquake interactions and the physical mechanisms at the origin of their occurrence are still intensively debated. Novel insights stem from recent results on the influence of the faulting style on the aftershock organisation in magnitude and time. Our study shows that the size of the aftershock zone depends on the fault geometry. We find that positive correlations among parameters controlling aftershock occurrence in time, energy and space are a stable feature of seismicity independently of magnitude range and geographic areas. We explain the ensemble of experimental findings by means of a description of the Earth Crust as an heterogeneous elastic medium coupled with a Maxwell viscoelastic asthenosphere. Our results show that heterogeneous stress distribution in an elastic layer combined with a coupling to a viscous flow are sufficient ingredients to describe the physics of aftershock triggering.

  15. Nonparametric Combinatorial Sequence Models

    NASA Astrophysics Data System (ADS)

    Wauthier, Fabian L.; Jordan, Michael I.; Jojic, Nebojsa

    This work considers biological sequences that exhibit combinatorial structures in their composition: groups of positions of the aligned sequences are "linked" and covary as one unit across sequences. If multiple such groups exist, complex interactions can emerge between them. Sequences of this kind arise frequently in biology but methodologies for analyzing them are still being developed. This paper presents a nonparametric prior on sequences which allows combinatorial structures to emerge and which induces a posterior distribution over factorized sequence representations. We carry out experiments on three sequence datasets which indicate that combinatorial structures are indeed present and that combinatorial sequence models can more succinctly describe them than simpler mixture models. We conclude with an application to MHC binding prediction which highlights the utility of the posterior distribution induced by the prior. By integrating out the posterior our method compares favorably to leading binding predictors.

  16. Data sensitivity in a hybrid STEP/Coulomb model for aftershock forecasting

    NASA Astrophysics Data System (ADS)

    Steacy, S.; Jimenez Lloret, A.; Gerstenberger, M.

    2014-12-01

    Operational earthquake forecasting is rapidly becoming a 'hot topic' as civil protection authorities seek quantitative information on likely near future earthquake distributions during seismic crises. At present, most of the models in public domain are statistical and use information about past and present seismicity as well as b-value and Omori's law to forecast future rates. A limited number of researchers, however, are developing hybrid models which add spatial constraints from Coulomb stress modeling to existing statistical approaches. Steacy et al. (2013), for instance, recently tested a model that combines Coulomb stress patterns with the STEP (short-term earthquake probability) approach against seismicity observed during the 2010-2012 Canterbury earthquake sequence. They found that the new model performed at least as well as, and often better than, STEP when tested against retrospective data but that STEP was generally better in pseudo-prospective tests that involved data actually available within the first 10 days of each event of interest. They suggested that the major reason for this discrepancy was uncertainty in the slip models and, in particular, in the geometries of the faults involved in each complex major event. Here we test this hypothesis by developing a number of retrospective forecasts for the Landers earthquake using hypothetical slip distributions developed by Steacy et al. (2004) to investigate the sensitivity of Coulomb stress models to fault geometry and earthquake slip, and we also examine how the choice of receiver plane geometry affects the results. We find that the results are strongly sensitive to the slip models and moderately sensitive to the choice of receiver orientation. We further find that comparison of the stress fields (resulting from the slip models) with the location of events in the learning period provides advance information on whether or not a particular hybrid model will perform better than STEP.

  17. The stress shadow problem in physics-based aftershock forecasting: Does incorporation of secondary stress changes help?

    NASA Astrophysics Data System (ADS)

    Segou, M.; Parsons, T.

    2014-06-01

    Main shocks are calculated to cast stress shadows across broad areas where aftershocks occur. Thus, a key problem with stress-based operational forecasts is that they can badly underestimate aftershock occurrence in the shadows. We examine the performance of two physics-based earthquake forecast models (Coulomb rate/state (CRS)) based on Coulomb stress changes and a rate-and-state friction law for their predictive power on the 1989 Mw = 6.9 Loma Prieta aftershock sequence. The CRS-1 model considers the stress perturbations associated with the main shock rupture only, whereas CRS-2 uses an updated stress field with stresses imparted by M ≥ 3.5 aftershocks. Including secondary triggering effects slightly improves predictability, but physics-based models still underestimate aftershock rates in locations of initial negative stress changes. Furthermore, CRS-2 does not explain aftershock occurrence where secondary stress changes enhance the initial stress shadow. Predicting earthquake occurrence in calculated stress shadow zones remains a challenge for stress-based forecasts, and additional triggering mechanisms must be invoked.

  18. A Jurassic Shock-Aftershock Earthquake Sequence Recorded by Small Clastic Pipes and Dikes within Dune Cross-Strata, Zion National Park, Utah

    NASA Astrophysics Data System (ADS)

    Loope, D. B.; Zlotnik, V. A.; Kettler, R. M.; Pederson, D. T.

    2012-12-01

    dune lee slope through a pipe, the erupted sand dried and was buried by climbing wind-ripple strata as the large dune continued to advance downwind. The mapped cluster recording eight distinct seismic events lies within thin-laminated sediment that was deposited by wind ripples during 1 m (~ 1 year) of southeastward dune migration. We conclude that the small pipes and dikes of our study sites are products of numerous >MM 5 earthquakes, some of which recurred at intervals of less than 2 months. We interpret one small cluster of pipes and dikes with well-defined upward terminations as a distinct shock-aftershock sequence. Because the largest modern earthquakes can produce surface liquefaction only up to about 175 km from their epicenters, the Jurassic epicenters must have been well within that distance. The tendency of modern plate boundaries to produce high-frequency aftershocks suggests that the epicenter for this Jurassic sequence lay to the southwest, within the plate boundary zone (not within continental rocks to the east). As eolian dunes steadily migrate over interdune surfaces underlain by water-saturated dune cross-strata, the thin, distinct laminae produced by the wind ripples that occupy dune toes can faithfully record high-frequency seismic events.

  19. Relation between aftershock parameters and geodetic slip models: Case study of the 2010 Mw8.8 Maule (Chile) and the 2011 Mw9.0 Tohoku-oki (Japan) earthquakes

    NASA Astrophysics Data System (ADS)

    Zakharova, Olga; Hainzl, Sebastian; Lange, Dietrich; Enescu, Bogdan

    2016-04-01

    The distribution of local stresses, which represents as well crustal heterogeneity, is the main factor for aftershock triggering. Though neither local stresses nor crustal heterogeneity are known in detail, some information of their distribution is implicitly represented by slip and coupling values on the mainshock fault interface. Taking these two concepts as the main assumptions, we perform a comprehensive analysis of the relation between aftershock characteristics and geodetic measurements on the mainshock fault interface. As a case study we select two megathrust events, the 2010 Mw8.8 Maule (Chile) and the 2011 Mw9.0 Tohoku-oki (Japan), due to the availability of rich aftershock data as well as of geodetic inversion models. To investigate the dependency between these data sets we firstly estimated the aftershock parameter distribution, using a modified ETAS model, which allows to take into account the mainshock rupture extension. Secondly we calculate the correlation between aftershock parameters and coseismic/postseismic slip and interseismic coupling. We find: (1) aftershocks tend to occur in the areas of high coseismic slip gradient, afterslip and interseismic coupling; (2) aftershock seismic moment is released preferentially in regions of large coseismic slip, coseismic slip gradient and interseismically locked areas; (3) anomalous aftershock parameters occur in the areas of reactivated fault systems. Moreover, we show that modified ETAS model outperforms the classical one in the cases when the mainshock rupture extension cannot be neglected and represented as a point source. One of the main restriction in the presented analysis is related to the large uncertainties of the inversion models, which limit the significance of our results.

  20. Some statistical features of the aftershock temporal behavior after the M7.4 Izmit earthquake of august 17, 1999 in Turkey

    NASA Astrophysics Data System (ADS)

    Gospodinov, D.; Fajtin, H.; Rangelov, B.; Marekova, E.

    2009-04-01

    An earthquake of magnitude Mw=7.4 struck 8 km. southeast of Izmit, Turkey at 3:02 AM local time on August 17, 1999. The earthquake occurred on one of the world's longest and best studied strike-slip (horizontal motion) faults - the east-west trending North Anatolian fault. Seismologists are not able to predict the timing and sizes of individual aftershocks but stochastic modeling allows determinationof probabilities for aftershocks and larger mainshocks duringintervals following the mainshock. The most widely applied stochastic model to depict aftershocks temporal distribution is the non- homogenous Poisson process with a decaying intensity, which follows the Modified Omori Formula (MOF) (Utsu, 1961). A more complex model, considering the triggering potential of each aftershock was developed by Ogata (1988) and it was named Epidemic Type Aftershock Sequence (ETAS) model. Gospodinov and Rotondi (2006) elaborated a Restricted Epidemic Type Aftershock Sequence (RETAS) model. The latter follows the general idea that only aftershocks stronger than some cut-off magnitude possess the capability to induce secondary aftershock activity. In this work we shall consider the Restricted Epidemic Type Aftershock Sequence (RETAS) model, for which the conditional intensity function turns out to be ‘ K0eα(Mi-M0)- λ (t|Ht) = + (t- ti + c)p ti < t Mi ≥ Mth (1) Here the summation occurs for all aftershocks with magnitude bigger than or equal to Mth, which took place before time. Leaving Mth to take all possible values, one can examine all RETAS model versions between the MOF and the ETAS model on the basis of the Akaike Information Criterion AIC (Akaike, 1974) AIC = - 2max log L+ 2k (2) where k is the number of parameters used in the model and logL is the logarithm of the likelihood function. Then for the model providing the best fit, we choose the one with the smallest AIC value. The purpose of this paper is to verify versions of the RETAS model (including the MOF and the

  1. Some facts about aftershocks to large earthquakes in California

    USGS Publications Warehouse

    Jones, Lucile M.; Reasenberg, Paul A.

    1996-01-01

    Earthquakes occur in clusters. After one earthquake happens, we usually see others at nearby (or identical) locations. To talk about this phenomenon, seismologists coined three terms foreshock , mainshock , and aftershock. In any cluster of earthquakes, the one with the largest magnitude is called the mainshock; earthquakes that occur before the mainshock are called foreshocks while those that occur after the mainshock are called aftershocks. A mainshock will be redefined as a foreshock if a subsequent event in the cluster has a larger magnitude. Aftershock sequences follow predictable patterns. That is, a sequence of aftershocks follows certain global patterns as a group, but the individual earthquakes comprising the group are random and unpredictable. This relationship between the pattern of a group and the randomness (stochastic nature) of the individuals has a close parallel in actuarial statistics. We can describe the pattern that aftershock sequences tend to follow with well-constrained equations. However, we must keep in mind that the actual aftershocks are only probabilistically described by these equations. Once the parameters in these equations have been estimated, we can determine the probability of aftershocks occurring in various space, time and magnitude ranges as described below. Clustering of earthquakes usually occurs near the location of the mainshock. The stress on the mainshock's fault changes drastically during the mainshock and that fault produces most of the aftershocks. This causes a change in the regional stress, the size of which decreases rapidly with distance from the mainshock. Sometimes the change in stress caused by the mainshock is great enough to trigger aftershocks on other, nearby faults. While there is no hard "cutoff" distance beyond which an earthquake is totally incapable of triggering an aftershock, the vast majority of aftershocks are located close to the mainshock. As a rule of thumb, we consider earthquakes to be

  2. Apparent triggering function of aftershocks resulting from rate-dependent incompleteness of earthquake catalogs

    NASA Astrophysics Data System (ADS)

    Hainzl, Sebastian

    2016-09-01

    The onset of the aftershock decay after main shocks is controversial. Physical models predict that the onset time is stress dependent, and catalog analysis shows a clear increase of the c value of the Omori-Utsu law with increasing main shock magnitude. However, earthquake catalogs are known to have variable quality and completeness levels; in particular, they miss events directly after main shocks. Thus, it has been also argued that the delayed onset of recorded aftershock activity triggered by large earthquakes is simply an artifact of the time-varying completeness. Here I utilize a recent approach describing the detection probability of earthquakes as function of the actual earthquake rate. I derive an analytical relation between apparent and true earthquake rate which only depends on the blind time of detection algorithms after the occurrence of an earthquake. This relation is tested and verified for synthetic simulations of Omori-type aftershock sequences. For a comparison, I analyze earthquake sequences occurred in Southern California and Taiwan, finding that the derived analytical decay function consistently explains the empirical aftershock activity in the catalogs. This indicates that the observed scaling of the Omori c value is mainly related to catalog incompleteness and not to any underlying physical process.

  3. The Mw 5.8 Virginia Earthquake of August 23, 2011 and its Aftershocks: A Shallow High Stress Drop Event

    NASA Astrophysics Data System (ADS)

    Ellsworth, W. L.; Imanishi, K.; Luetgert, J. H.; Kruger, J.; Hamilton, J.

    2011-12-01

    We analyze the hypocentral distribution and source parameters of the aftershocks of the Virginia Earthquake of August 23, 2011 using a temporary array of telemetered instruments deployed within 20 km of the main shock. Our data come from four USGS NetQuakes accelerometers and seven IRIS/PASSCAL seismometers that were established within a few days of the earthquake. Aftershock seismograms at these near-source stations are characterized by impulsive, high-frequency P and S phases at most sites. In addition, we use the five closest permanent stations (60 - 310 km distance) to analyze the main shock. Hypocenters, crustal velocity model and station corrections were determined using the program VELEST (Kissling, et al, 1994). The aftershocks define a 10-km-long, N 30 degree E striking, 45 degree ESE dipping fault. This fault plane agrees well with the USGS moment tensor solutions for the main shock. Aftershock depths range from 2.5 to 8 km, placing the sequence in the Cambrian metamorphic rocks of the Eastern Piedmont thrust sheet. We relocated the main shock relative to a well-located Mw 3.5 aftershock using the P-wave arrival times at the five permanent stations. The main shock epicenter lies in the middle of the aftershock zone. Its focal depth, although not well constrained, is similar to the aftershocks. A crustal-scale seismic reflection profile was acquired by the USGS in 1981 along I-64 just 4 km southwest of the nearest aftershocks. This profile runs nearly parallel to the dip direction of the aftershock zone and has been interpreted to contain many ESE-dipping reverse faults in the allochthonous upper crust (Harris et al., 1986; Pratt, et al., 1988). When projected onto the reflection profile the aftershocks locate within a relatively non-reflective zone bounded above and below by prominent bands of more shallowly dipping reflectors reported by Pratt et al. (1988) raising the question whether or not the earthquake reactivated a pre-existing fault. Seismic

  4. The Prediction of Spatial Aftershock Probabilities (PRESAP)

    NASA Astrophysics Data System (ADS)

    McCloskey, J.

    2003-12-01

    extent to which this is scientifically feasible in terms of our understanding of the physical phenomena which control the variation of seismicity following a large event due to stress redistribution and practically possible given present limitations on data availability, data quality and computational or data transfer speeds. The project is divided into a number of elements designed to reflect the temporal sequence of tasks that must be undertaken for the prediction of aftershock hazard. These tasks include determining a time-indexed sequence of slip distributions for both real and synthetic events, calculating a suite of time-indexed stress perturbations and quantitatively comprising predicted and observed aftershock distributions, and developing techniques for predicting likely strong ground motion from the predicted spatial distribution of aftershocks.

  5. Plate coupling strength inferred from aftershock area expansion patterns and associated plate age

    NASA Astrophysics Data System (ADS)

    Tajima, F. C.

    2010-12-01

    Fault zone heterogeneity or plate boundary coupling in subduction zones has been debated repeatedly in numerous studies to understand the mechanisms that control characteristics of earthquake occurrence, i.e., typical moment release and degree of complexity of a mainshock rupture, and subsequent aftershock activity. Here we revisit a global survey of aftershock area expansion patterns of shallow large earthquakes (M≥˜7.5) focusing on the plate subduction boundaries (Tajima and Kanamori, 1985a,b), and attempt to relate the plate coupling strength to the sea floor age data compiled recently (Müller et al., 2008). The aftershock area S(t) (km2) was determined applying an objective method to draw contour maps for the seismic energy released from an aftershock sequence (i.e., 1015.6erg/100km2/day for the one-day aftershock area). Then, the expansion patterns are investigated as a function of time t (day) after the first day of aftershock activity, by the ratio of the aftershock area η(t) = S(t)/S(1) as well as the ratio of its length L(t) (km), ηl(t) = L(t)/L(1). The survey determined distinct regional variation that was interpreted in terms of plate coupling strength. In the subduction zones of Mexico, Alaska and parts of the South America the aftershock areas of large to great earthquakes show little expansion, and the coupling of the subducting and overlying plates is considered to be strong. In these regions relatively young (≤Miocene) plates are subducting beneath continents. In the Kuriles the aftershock area expansion of large events is widthwise indicating distinct boundaries lengthwise. The subduction zones are interpreted to be characterized by moderate to strong interplate coupling of two oceanic plates of a similar age (˜Cretaceus). Repeated large earthquakes in the Kuriles may have created “mature faults” of relatively loose mechanical coupling within distinct boundaries of strong coupling (asperities and barriers). In contrast, the aftershock

  6. Aftershock relocation and frequency-size distribution, stress inversion and seismotectonic setting of the 7 August 2013 M = 5.4 earthquake in Kallidromon Mountain, central Greece

    NASA Astrophysics Data System (ADS)

    Ganas, Athanassios; Karastathis, Vassilios; Moshou, Alexandra; Valkaniotis, Sotirios; Mouzakiotis, Evangelos; Papathanassiou, George

    2014-03-01

    On August 7, 2013 a moderate earthquake (NOA ML = 5.1, NOA Mw = 5.4) occurred in central Kallidromon Mountain, in the Pthiotis region of central Greece. 2270 aftershocks were relocated using a modified 1-D velocity model for this area. The b-value of the aftershock sequence was b = 0.85 for a completeness magnitude of Mc = 1.7. The rate of aftershock decay was determined at p = 0.63. The spatial distribution of the aftershock sequence points towards the reactivation of a N70° ± 10°E striking normal fault at crustal depths between 8 and 13 km. A NNW-SSE cross-section imaged the activation of a steep, south dipping normal fault. A stress inversion analysis of 12 focal mechanisms showed that the minimum horizontal stress is extensional at N173°E. No primary surface ruptures were observed in the field; however, the earthquake caused severe damage in the villages of the Kallidromon area. The imaged fault strike and the orientation of the long-axis of the aftershock sequence distribution are both at a high-angle to the strike of known active faults in this area of central Greece. We interpret the Kallidromon seismic sequence as release of extensional seismic strain on secondary, steep faults inside the Fokida-Viotia crustal block.

  7. Source modeling of the 2015 Mw 7.8 Nepal (Gorkha) earthquake sequence: Implications for geodynamics and earthquake hazards

    USGS Publications Warehouse

    McNamara, Daniel E.; Yeck, William; Barnhart, William D.; Schulte-Pelkum, V.; Bergman, E.; Adhikari, L. B.; Dixit, Amod; Hough, S.E.; Benz, Harley M.; Earle, Paul

    2016-01-01

    The Gorkha earthquake on April 25th, 2015 was a long anticipated, low-angle thrust-faulting event on the shallow décollement between the India and Eurasia plates. We present a detailed multiple-event hypocenter relocation analysis of the Mw 7.8 Gorkha Nepal earthquake sequence, constrained by local seismic stations, and a geodetic rupture model based on InSAR and GPS data. We integrate these observations to place the Gorkha earthquake sequence into a seismotectonic context and evaluate potential earthquake hazard.Major results from this study include (1) a comprehensive catalog of calibrated hypocenters for the Gorkha earthquake sequence; (2) the Gorkha earthquake ruptured a ~ 150 × 60 km patch of the Main Himalayan Thrust (MHT), the décollement defining the plate boundary at depth, over an area surrounding but predominantly north of the capital city of Kathmandu (3) the distribution of aftershock seismicity surrounds the mainshock maximum slip patch; (4) aftershocks occur at or below the mainshock rupture plane with depths generally increasing to the north beneath the higher Himalaya, possibly outlining a 10–15 km thick subduction channel between the overriding Eurasian and subducting Indian plates; (5) the largest Mw 7.3 aftershock and the highest concentration of aftershocks occurred to the southeast the mainshock rupture, on a segment of the MHT décollement that was positively stressed towards failure; (6) the near surface portion of the MHT south of Kathmandu shows no aftershocks or slip during the mainshock. Results from this study characterize the details of the Gorkha earthquake sequence and provide constraints on where earthquake hazard remains high, and thus where future, damaging earthquakes may occur in this densely populated region. Up-dip segments of the MHT should be considered to be high hazard for future damaging earthquakes.

  8. Asymmetric Earthquake Aftershock Distributions Resulting from Timing Within the Seismic Cycle

    NASA Astrophysics Data System (ADS)

    McGuire, J. J.; Collins, J. A.; Boettcher, M. S.; Roland, E. C.

    2010-12-01

    Aftershock sequences are a well documented result of changes in the crustal stress-field resulting from nearby large earthquakes, yet there is typically little (or no) constraint on the initial stress level of the “receiver fault” where the triggered aftershock occurs. Thus, many popular physical and stochastic models of aftershock triggering do not account for the absolute stress-level on a receiver fault, and the importance of this stress level (relative to a fault’s failure threshold) is not easily studied. In 2008 we recorded a series of westward propagating ruptures that marked the end of the most recent seismic cycle on the Gofar transform fault using an array of Ocean Bottom Seismometers (OBSs). The end of the 2002-2008 seismic cycle on the Gofar fault included a series of 4 major rupture events (either M6 earthquakes or large seismic swarms) that propagated ~90 km along the strike of the fault from east to west over the course of 1.5 years. Our OBS dataset covered the last 3 of these events and recorded over 200,000 microearthquakes. Each of the 3 rupture events produced a spatially asymmetric aftershock distribution. On the eastern side of each slipping zone, where the stress is lower because the fault has already ruptured in its cycle-ending event, the large rupture events do not change the seismicity-rate. In contrast, on the western side, where stress is high because the area is nearing the end of it’s seismic cycle, there is a clear increase in seismicity rate (i.e. aftershocks). This asymmetry demonstrates the importance of absolute stress-levels in earthquake triggering. This observation contrasts with the Rate-State seismicity model (Dieterich, 1994), which predicts that seismicity-rate increases will depend only on stressing-rate and the magnitude of a static stress change. Since static stress changes from large ruptures are fairly symmetric along a geometrically simple strike slip fault, like Gofar, the observed aftershock asymmetry

  9. Early aftershocks and afterslip surrounding the 2015 Mw 8.4 Illapel rupture

    NASA Astrophysics Data System (ADS)

    Huang, Hui; Xu, Wenbin; Meng, Lingsen; Bürgmann, Roland; Baez, Juan Carlos

    2017-01-01

    On 16 September 2015, the Mw 8.4 Illapel earthquake ruptured a section of the subduction thrust on the west coast of central Chile. The mainshock was followed by numerous aftershocks including some normal-faulting events near the trench. We apply a template matching approach to improve the completeness of early aftershocks within one month of the mainshock. To constrain the distribution of afterslip, we utilize repeating earthquakes among the aftershocks and perform a joint slip inversion of postseismic GPS and InSAR data. The results show that the aftershock zone abruptly expands to the south ∼14 h after the mainshock while growing relatively continuously to the north within the first day. The repeating earthquakes accompanying the early expansion suggest that aseismic afterslip on the subduction thrust surrounding the coseismic rupture is an important triggering mechanism of aftershocks in addition to stress transfer or poroelastic effects. An energetic earthquake sequence near the trench initiated with a M 4.6 event ∼3.5 h after the mainshock, suggesting delayed triggering by the static or dynamic stress changes induced by the mainshock. The spatial distribution of repeating earthquakes and the geodetic-inverted afterslip are consistent and appear to wrap around the large coseismic slip patch. Both data sets suggest that the largest cumulative afterslip is located at ∼30.5°S to the north of the mainshock rupture zone. The estimated postseismic moment released in the first ∼24 days of afterslip is equivalent to an earthquake of Mw 7.5. The afterslip illuminates the velocity strengthening sections of the plate interface that surround the mainshock rupture, consistent with plate coupling models inferred from interseismic GPS velocities.

  10. The aftershock processes of strong earthquakes in the Western Caucasus

    NASA Astrophysics Data System (ADS)

    Baranov, S. V.; Gabsatarova, I. P.

    2015-05-01

    The aftershock processes of the four strong earthquakes that occurred in the Western Caucasus from 1991 to June 2013 are considered. The main shocks of these earthquakes include the first Racha earthquake (April 29, 1991, Ms = 6.9); second Racha earthquake (June 15, 1991, Ms = 6.2); Oni earthquake (September 7, 2009, Ms = 5.8); and East Black Sea earthquake (December 23, 2012, Ms = 5.6). Based on the simulations with the LPL relaxation model and the ETAS model of triggered seismicity, the differences in the properties of the aftershock processes and the characteristics of the fault zones accommodating the main shocks are revealed. The nonrelaxation character of the aftershocks from the East Black Sea earthquake is established. It is hypothesized and validated that this is a result of the violation of the fluid-dynamic equilibrium in the fault zone due to the destruction of the gas hydrate layer by the main shock and strong aftershocks.

  11. Foreshocks and aftershocks of the Great 1857 California earthquake

    USGS Publications Warehouse

    Meltzner, A.J.; Wald, D.J.

    1999-01-01

    The San Andreas fault is the longest fault in California and one of the longest strike-slip faults anywhere in the world, yet we know little about many aspects of its behavior before, during, and after large earthquakes. We conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 M 7.9 Fort Tejon earthquake on the central and southern segments of the fault. We began by searching archived first-hand accounts from 1857 through 1862, by grouping felt reports temporally, and by assigning modified Mercalli intensities to each site. We then used a modified form of the grid-search algorithm of Bakum and Wentworth, derived from empirical analysis of modern earthquakes, to find the location and magnitude most consistent with the assigned intensities for each of the largest events. The result confirms a conclusion of Sieh that at least two foreshocks ('dawn' and 'sunrise') located on or near the Parkfield segment of the San Andreas fault preceded the mainshock. We estimate their magnitudes to be M ~ 6.1 and M ~ 5.6, respectively. The aftershock rate was below average but within one standard deviation of the number of aftershocks expected based on statistics of modern southern California mainshock-aftershock sequences. The aftershocks included two significant events during the first eight days of the sequence, with magnitudes M ~ 6.25 and M ~ 6.7, near the southern half of the rupture; later aftershocks included a M ~ 6 event near San Bernardino in December 1858 and a M ~ 6.3 event near the Parkfield segment in April 1860. From earthquake logs at Fort Tejon, we conclude that the aftershock sequence lasted a minimum of 3.75 years.

  12. Active Tectonics in the Central Chilean Andes: 3D Tomography Based on the Aftershock Sequence of the 28 August 2004 Shallow Crustal Earthquake

    NASA Astrophysics Data System (ADS)

    Comte, D.; Farias, M.; Charrier, R.; Gonzalez, A.

    2008-12-01

    Most of the seismological research in the Andes has been mainly oriented to the detection and understanding of the seismicity associated with megathrust earthquakes that characterize the subduction environment that governs the Andean tectonics. However, deployments of temporary networks have allowed the detection of intense crustal seismicity beneath the Chilean forearc-arc region. The temporary seismic network deployed along the Las Leñas and Pangal river valleys (34°25'S), between January and May 2004 permitted to better constrain the abundant shallow intra-continental seismicity previously detected in that region. Although most of the seismicity is randomly distributed in the region, several microearthquakes occur along the trace of the major El Fierro fault-system. This system is well recognized between 33°30' and 35°15'S and is located at or close to the eastern contact between Mesozoic and Cenozoic deposits in the Principal Cordillera and, locally, below active volcanoes, being considered to have participated in the extension and tectonic inversion of a widely extended (>600 km long) Cenozoic basin along the Principal Cordillera. Further south, at 35°S, a Mw=6.5 strike-slip shallow earthquake occurred on August 28, 2004, near of the headwater of the Teno river, close to the Planchon volcano. A 3D detailed Vp and Vs velocities determination was obtained along the 2004 earthquake aftershock area. The aftershocks are distributed along one branch of the El Fierro fault system, with a NNE-SSW direction and depths lower than 15 km. The rupture zone coincides with a sharp contrast in Vp and Vs, also in coincidence with the presence of hydrothermal fluids, gypsum diapers and the volcanic arc, suggesting rheological contrast controlling deformation. At the surface, this zone present an intense contractive deformation produced during the Neogene, which differs from what can be observed in other regions. Present day deformation related to seismicity has no

  13. Single-link cluster analysis of earthquake aftershocks: Decay laws and regional variations

    SciTech Connect

    Davis, S.D.; Frohlich, C. )

    1991-04-10

    Using single-link cluster analysis, the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth. For International Seismological Centre earthquakes of m{sub b}{ge}4.8, they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences. Even after accounting for differences in detectability and maximum magnitude, they find that ridge-transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes. Among different subduction zones, they find that zones with high moment release rates possess larger aftershock sequences. Comparing ridge-transform zones, they find those with slower spreading rates possess larger aftershock sequences. By transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero, they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means. Secondary events determined by single-link cluster analysis follow a modified Omori's (power law) decay for time separations of 0.1 day to 20 days from the parent event, with p values ranging from 0.539 {plus minus} 0.022 (intermediate- and deep-focus earthquakes) to 0.928 {plus minus} 0.024 (ridge-transform earthquakes). They find that earthquake foreshocks and multiplets also follow a modified Omori's law. At greater times from the main shock the decay is steeper than a power law decay, more like an exponential decay. Aftershocks in the Adak catalog (m{sub b}{ge}2.0) show a marked decrease in activity between 40 and 50 km depth. They speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures.

  14. Spatial correlation of aftershock locations and on-fault main shock properties

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Schorlemmer, D.; Wiemer, S.; Mai, P. M.

    2006-08-01

    We quantify the correlation between spatial patterns of aftershock hypocenter locations and the distribution of coseismic slip and stress drop on a main shock fault plane using two nonstandard statistical tests. Test T1 evaluates if aftershock hypocenters are located in low-slip regions (hypothesis H1), test T2 evaluates if aftershock hypocenters occur in regions of increased shear stress (hypothesis H2). In the tests, we seek to reject the null hypotheses H0: Aftershock hypocenters are not correlated with (1) low-slip regions or (2) regions of increased shear stress, respectively. We tested the hypotheses on four strike-slip events for which multiple earthquake catalogs and multiple finite fault source models of varying accuracy exist. Because we want to retain earthquake clustering as the fundamental feature of aftershock seismicity, we generate slip distributions using a random spatial field model and derive the stress drop distributions instead of generating seismicity catalogs. We account for uncertainties in the aftershock locations by simulating them within their location error bounds. Our findings imply that aftershocks are preferentially located in regions of low-slip (u ≤ ?umax) and of increased shear stress (Δσ < 0). In particular, the correlation is more significant for relocated than for general network aftershock catalogs. However, the results show that stress drop patterns provide less information content on aftershock locations. This implies that static shear stress change of the main shock may not be the governing process for aftershock genesis.

  15. The global aftershock zone

    USGS Publications Warehouse

    Parsons, Thomas E.; Margaret Segou,; Warner Marzocchi,

    2014-01-01

    The aftershock zone of each large (M ≥ 7) earthquake extends throughout the shallows of planet Earth. Most aftershocks cluster near the mainshock rupture, but earthquakes send out shivers in the form of seismic waves, and these temporary distortions are large enough to trigger other earthquakes at global range. The aftershocks that happen at great distance from their mainshock are often superposed onto already seismically active regions, making them difficult to detect and understand. From a hazard perspective we are concerned that this dynamic process might encourage other high magnitude earthquakes, and wonder if a global alarm state is warranted after every large mainshock. From an earthquake process perspective we are curious about the physics of earthquake triggering across the magnitude spectrum. In this review we build upon past studies that examined the combined global response to mainshocks. Such compilations demonstrate significant rate increases during, and immediately after (~ 45 min) M > 7.0 mainshocks in all tectonic settings and ranges. However, it is difficult to find strong evidence for M > 5 rate increases during the passage of surface waves in combined global catalogs. On the other hand, recently published studies of individual large mainshocks associate M > 5 triggering at global range that is delayed by hours to days after surface wave arrivals. The longer the delay between mainshock and global aftershock, the more difficult it is to establish causation. To address these questions, we review the response to 260 M ≥ 7.0 shallow (Z ≤ 50 km) mainshocks in 21 global regions with local seismograph networks. In this way we can examine the detailed temporal and spatial response, or lack thereof, during passing seismic waves, and over the 24 h period after their passing. We see an array of responses that can involve immediate and widespread seismicity outbreaks, delayed and localized earthquake clusters, to no response at all. About 50% of the

  16. Postseismic relaxation and aftershocks

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Yu, S.-B.

    2007-01-01

    Perfettini et al. (2005) suggested that the temporal dependence of surface displacements u(t) measured in the epicentral area following an earthquake is related to N(t), the cumulative number of aftershocks, by the equation u(t) = a + bt + cN(t) + d(1 - e-??t), where a, b, c, d, and ?? are constants chosen to fit the data and t is the postearthquake time. N(t) appears in the expression for u(t) because both the aftershocks and a portion of u(t) are thought to be driven by the same source, postseismic fault creep at subseismogenic depths on the downdip extension of the coseismic rupture. We show that this equation with the actually observed N(t) fits the postseismic displacements recorded on several baselines following each of five earthquakes: 1999 M7.6 Chi-Chi (Taiwan), 1999 M7.1 Hector Mine (southern California), 2002 M7.9 Denali (central Alaska), 2003 M6.5 San Simeon (central California), and 2004 M6.0 Parkfield (central California) earthquakes. Although there are plausible physical interpretations for each of the terms in the expression for u(t), the large number of adjustable constants (a, b, c, d, and ??) involved in fitting the rather simple postseismic displacements diminishes the significance of the fit. Because the observed N(t) is well fit by the modified Omori's law, fault creep at depth presumably exhibits the same temporal dependence. That dependence could be explained if the rheology of the fault downdip from the coseismic rupture is consistent with ordinary transient creep. Montesi (2004) demonstrated that power law creep across a shear zone at depth would also produce that temporal signal.

  17. A Fluid-driven Earthquake Cycle, Omori's Law, and Fluid-driven Aftershocks

    NASA Astrophysics Data System (ADS)

    Miller, S. A.

    2015-12-01

    Few models exist that predict the Omori's Law of aftershock rate decay, with rate-state friction the only physically-based model. ETAS is a probabilistic model of cascading failures, and is sometimes used to infer rate-state frictional properties. However, the (perhaps dominant) role of fluids in the earthquake process is being increasingly realised, so a fluid-based physical model for Omori's Law should be available. In this talk, I present an hypothesis for a fluid-driven earthquake cycle where dehydration and decarbonization at depth provides continuous sources of buoyant high pressure fluids that must eventually make their way back to the surface. The natural pathway for fluid escape is along plate boundaries, where in the ductile regime high pressure fluids likely play an integral role in episodic tremor and slow slip earthquakes. At shallower levels, high pressure fluids pool at the base of seismogenic zones, with the reservoir expanding in scale through the earthquake cycle. Late in the cycle, these fluids can invade and degrade the strength of the brittle crust and contribute to earthquake nucleation. The mainshock opens permeable networks that provide escape pathways for high pressure fluids and generate aftershocks along these flow paths, while creating new pathways by the aftershocks themselves. Thermally activated precipitation then seals up these pathways, returning the system to a low-permeability environment and effective seal during the subsequent tectonic stress buildup. I find that the multiplicative effect of an exponential dependence of permeability on the effective normal stress coupled with an Arrhenius-type, thermally activated exponential reduction in permeability results in Omori's Law. I simulate this scenario using a very simple model that combines non-linear diffusion and a step-wise increase in permeability when a Mohr Coulomb failure condition is met, and allow permeability to decrease as an exponential function in time. I show very

  18. Decay of aftershock density with distance indicates triggering by dynamic stress

    USGS Publications Warehouse

    Felzer, K.R.; Brodsky, E.E.

    2006-01-01

    The majority of earthquakes are aftershocks, yet aftershock physics is not well understood. Many studies suggest that static stress changes trigger aftershocks, but recent work suggests that shaking (dynamic stresses) may also play a role. Here we measure the decay of aftershocks as a function of distance from magnitude 2-6 mainshocks in order to clarify the aftershock triggering process. We find that for short times after the mainshock, when low background seismicity rates allow for good aftershock detection, the decay is well fitted by a single inverse power law over distances of 0.2-50 km. The consistency of the trend indicates that the same triggering mechanism is working over the entire range. As static stress changes at the more distant aftershocks are negligible, this suggests that dynamic stresses may be triggering all of these aftershocks. We infer that the observed aftershock density is consistent with the probability of triggering aftershocks being nearly proportional to seismic wave amplitude. The data are not fitted well by models that combine static stress change with the evolution of frictionally locked faults. ?? 2006 Nature Publishing Group.

  19. Aftershock process of Chu earthquake

    NASA Astrophysics Data System (ADS)

    Emanov, Alexey; Leskova, Ekaterina; Emanov, Aleksandr; Kolesnikov, Yury; Fateyev, Aleksandr

    2010-05-01

    Chu earthquake of 27.09.2003, Ms =7.3 occurred in joint zone of Chagan-Uzun raised block with North-Chu ridge. Epicentral zone cover a series of contrast geological structures of Mountain Altai (two hollows: Chu and Kurai, devided by Chagan-Uzun block, and mountain range, franking them,: Nort-Chu, Kurai, South-Chu, Aigulak). The seismic process occurred in zone of expressive block structure, and this is embodied in its space-time structure. The high accuracy of hypocental construction in epicenral zone of Chu earthquake is provided by local network of seismological stations (fifteen stations) and experiments with temporary station network in this zone (20-50 stations). The first stage of aftershock process formation is connected with Chagan-Uzun block. The second large aftershock of 01.10.2003 changes cardinally spatial pattern of aftershock process. Instead of round area an elongate aftershock area is formed along boundary of Kurai hollow with North-Chu ridge. In the following process spread out in north-west angle of Chu hollow. Linear elongate aftershock area is subdivided into four elements. The north-west element has form of horse tail, starting as a line in area of outlet of Aktru River in Kurai hollow, and ramifies short of settlement Chibit. Slope of plane of aftershocks for this element is determined from hollow under North-Chu ridge. The seismic process is going not along boundary hollow-mountain ridge, but displaced in hollow side. The central part of element - this are mainly horizontal shift faults, and outlying districts have pronounced vertical components of displacements. The second element stretches from Aktru River to Chagan-Uzun block. Earthquake epicenters in plane make two curved parallel lines. In the angle of Chagan-Uzun block are ceiling amount of uplifts. The third element is the boundary of Chagan-Uzun block with North-Chu ridge. The forth element is formed by aftershocks, leaving in range of Chu hollow. Areal dispersal of earthquakes is

  20. Coseismic deformation fields and a fault slip model for the Mw7.8 mainshock and Mw7.3 aftershock of the Gorkha-Nepal 2015 earthquake derived from Sentinel-1A SAR interferometry

    NASA Astrophysics Data System (ADS)

    Zuo, Ronghu; Qu, Chunyan; Shan, XinJian; Zhang, Guohong; Song, Xiaogang

    2016-08-01

    Coseismic deformation fields caused by the moment magnitude (Mw)7.8 mainshock and Mw7.3 aftershock of the 2015 Gorkha-Nepal earthquake are obtained by analyzing Sentinel-1A/IW ascending and descending interferometry data. Results show that the deformation field associated with the Mw7.8 mainshock roughly resembles a prolate ellipse, extending from the epicenter about 20° east by south. The main region of deformation is about 160 km by 110 km, comprising a large southern area of uplift, and a small northern area of subsidence. Assuming that rupture occurred in a homogeneous elastic half-space, the coseismic fault slip models of the mainshock and aftershock are inverted based on a shallow dip fault constrained by the three data sets, Sentinel-1A/IW descending data, ascending data, and ALOS-2 descending data, separately or in combination. Mainshock slip distributions generated from all three data sets are similar, and inversion constrained by all three in combination reveal a comprehensive fault slip model. Indeed, coseismic slip is mainly distributed within a narrow 40 km zone to the north of the Main Frontal Trust (MFT), and at 6-15 km subsurface depth. In addition, the maximum slip in this event was about 5.1 m, the Mw7.8 mainshock ruptured the deep part of the seismogenic zone, while the region between the southern boundary of the rupture area and the MFT remained locked. Therefore, a considerable earthquake risk remains to the south of Kathmandu. The inverted coseismic slip of the Mw7.3 aftershock was concentrated in a small area, close to, and southeast of the epicenter, with maximum displacement of about 3 m. Finally, because there is no overlap between the two slip areas of the mainshock and aftershock, the gap between them, about 15 km in length, has additional potential to generate future earthquakes.

  1. Magnitude estimates of two large aftershocks of the 16 December 1811 New Madrid earthquake

    USGS Publications Warehouse

    Hough, S.E.; Martin, S.

    2002-01-01

    The three principal New Madrid mainshocks of 1811-1812 were followed by extensive aftershock sequences that included numerous felt events. Although no instrumental data are available for either the mainshocks or the aftershocks, available historical accounts do provide information that can be used to estimate magnitudes and locations for the large events. In this article we investigate two of the largest aftershocks: one near dawn following the first mainshock on 16 December 1811, and one near midday on 17 December 1811. We reinterpret original felt reports to obtain a set of 48 and 20 modified Mercalli intensity values of the two aftershocks, respectively. For the dawn aftershock, we infer a Mw of approximately 7.0 based on a comparison of its intensities with those of the smallest New Madrid mainshock. Based on a detailed account that appears to describe near-field ground motions, we further propose a new fault rupture scenario for the dawn aftershock. We suggest that the aftershock had a thrust mechanism and occurred on a southeastern limb of the Reelfoot fault. For the 17 December 1811 aftershock, we infer a Mw of approximately 6.1 ?? 0.2. This value is determined using the method of Bakun et al. (2002), which is based on a new calibration of intensity versus distance for earthquakes in central and eastern North America. The location of this event is not well constrained, but the available accounts suggest an epicenter beyond the southern end of the New Madrid Seismic Zone.

  2. Stress shadows of the 2011 Mw=9.0 Tohoku-oki, Japan, earthquake: Suppressed aftershocks of the 2008 Mw=6.6 Iwate-Miyagi inland earthquake

    NASA Astrophysics Data System (ADS)

    Suzuki, Y.; Toda, S.

    2013-12-01

    Numerous papers of stress triggering have been published since 1990s. Among them, only a few studies have evidently shown that seismicity shut down or suppression associated with static Coulomb stress decrease (hereinafter 'stress shadow'). The reason only fewer reports exist is its restrictive conditions to detect stress shadow. To prove statistical significance, the following conditions are satisfied: (i) high seismicity rate before a disturbance, (ii) long elapsed time required since the disturbance, (iii) negative Coulomb stress on most of the pre-existing faults in the area. A preceding aftershocks before the disturbance is often used to satisfy the condition (i) (e.g. Toda and Stein, 2003). But one must strictly consider a temporal decay of aftershocks to fairly compare the post-disturbance rate with the pre-disturbance rate. To calibrate such potential bias, we employ the Epidemic-Type Aftershock Sequence (ETAS) model (Ogata, 1988) which can simulate the temporal decay and effect of secondary aftershocks. Here, we use the Japan Meteorological Agency (JMA) earthquake catalog from 2000 to June 2013 (depth≤25km) and examine any deviation of observed rate from theoretical seismicity predicted by the ETAS model after the 2011 Tohoku-oki earthquake. We here focus on aftershock areas of the 2008 Iwate-Miyagi inland earthquake (Mw 6.6), the 2003 North-Miyagi earthquake (Mw 6.0) and the 2010 Fukushima earthquake (Mw 5.5), all of which are mostly supposed to satisfy all the conditions. To detect seismicity rate change between before and after a stress perturbation, one must estimate the minimum magnitude of completeness (Mc) throughout the testing period. Based on a report of JMA (2012) and our own magnitude-frequency plots, we set Mc=3.0 in the Iwate-Miyagi inland earthquake and the North-Miyagi earthquake, and Mc=2.0 in the Fukushima earthquake regions. To rigorously define their aftershock zones, we calculate seismicity rate before (Rb) and after (Ra) their own

  3. Tsunamigenic Aftershocks From Large Strike-Slip Earthquakes: An Example From the November 16, 2000 Mw=8.0 New Ireland, Papua New Guinea, Earthquake

    NASA Astrophysics Data System (ADS)

    Geist, E.; Parsons, T.; Hirata, K.; Hirata, K.

    2001-12-01

    Two reverse mechanism earthquakes (M > 7) were triggered by the November 16, 2000 Mw=8.0 New Ireland (Papua New Guinea) left-lateral, strike-slip earthquake. The mainshock rupture initiated in the Bismarck Sea and propagated unilaterally to the southeast through the island of New Ireland and into the Solomon Sea. Although the mainshock caused a local seiche in the bay near Rabaul (New Britain) with a maximum runup of 0.9 m, the main tsunami observed on the south coast of New Britain, New Ireland, and Bougainville (maximum runup approximately 2.5-3 m), appears to have been caused by the Mw=7.4 aftershock 2.8 hours following the mainshock. It is unclear whether the second Mw=7.6 aftershock on November 17, 2000 (40 hours after the mainshock) also generated a tsunami. Analysis and modeling of the available tsunami information can constrain the source parameters of the tsunamigenic aftershock(s) and further elucidated the triggering mechanism. Preliminary stress modeling indicates that because the location of the first Mw=7.4 aftershock is located near the rupture termination of the mainshock, stress calculations are especially sensitive to the location of both ruptures and the assumed coefficient of friction. A similar example of a triggered tsunamigenic earthquake occurred following the 1812 Wrightwood (M ~7.5) earthquake in southern California as discussed by Deng and Sykes (1996, GRL, p. 1155-1158). In this case, they show that strike-slip rupture on the San Andreas fault produced coseismic stress changes that triggered the Santa Barbara Channel earthquake (M ~7.1), 13 days later. The mechanism for the Santa Barbara Channel event appears to have been an oblique thrust event. The November 2000 New Ireland earthquake sequence provides an important analog for studying the potential for tsunamigenic aftershocks following large San Andreas earthquakes in southern California.

  4. Aftershock communication during the Canterbury Earthquakes, New Zealand: implications for response and recovery in the built environment

    USGS Publications Warehouse

    Julia Becker,; Wein, Anne; Sally Potter,; Emma Doyle,; Ratliff, Jamie L.

    2015-01-01

    On 4 September 2010, a Mw7.1 earthquake occurred in Canterbury, New Zealand. Following the initial earthquake, an aftershock sequence was initiated, with the most significant aftershock being a Mw6.3 earthquake occurring on 22 February 2011. This aftershock caused severe damage to the city of Christchurch and building failures that killed 185 people. During the aftershock sequence it became evident that effective communication of aftershock information (e.g., history and forecasts) was imperative to assist with decision making during the response and recovery phases of the disaster, as well as preparedness for future aftershock events. As a consequence, a joint JCDR-USGS research project was initiated to investigate: • How aftershock information was communicated to organisations and to the public; • How people interpreted that information; • What people did in response to receiving that information; • What information people did and did not need; and • What decision-making challenges were encountered relating to aftershocks. Research was conducted by undertaking focus group meetings and interviews with a range of information providers and users, including scientists and science advisors, emergency managers and responders, engineers, communication officers, businesses, critical infrastructure operators, elected officials, and the public. The interviews and focus group meetings were recorded and transcribed, and key themes were identified. This paper focuses on the aftershock information needs for decision-making about the built environment post-earthquake, including those involved in response (e.g., for building assessment and management), recovery/reduction (e.g., the development of new building standards), and readiness (e.g. between aftershocks). The research has found that the communication of aftershock information varies with time, is contextual, and is affected by interactions among roles, by other information, and by decision objectives. A number

  5. Larger aftershocks happen farther away: nonseparability of magnitude and spatial distributions of aftershocks

    USGS Publications Warehouse

    Van Der Elst, Nicholas; Shaw, Bruce E.

    2015-01-01

    Aftershocks may be driven by stress concentrations left by the main shock rupture or by elastic stress transfer to adjacent fault sections or strands. Aftershocks that occur within the initial rupture may be limited in size, because the scale of the stress concentrations should be smaller than the primary rupture itself. On the other hand, aftershocks that occur on adjacent fault segments outside the primary rupture may have no such size limitation. Here we use high-precision double-difference relocated earthquake catalogs to demonstrate that larger aftershocks occur farther away than smaller aftershocks, when measured from the centroid of early aftershock activity—a proxy for the initial rupture. Aftershocks as large as or larger than the initiating event nucleate almost exclusively in the outer regions of the aftershock zone. This observation is interpreted as a signature of elastic rebound in the earthquake catalog and can be used to improve forecasting of large aftershocks.

  6. Aftershock Prediction for High-Frequency Financial Markets' Dynamics

    NASA Astrophysics Data System (ADS)

    Baldovin, Fulvio; Camana, Francesco; Caraglio, Michele; Stella, Attilio L.; Zamparo, Marco

    The occurrence of aftershocks following a major financial crash manifests the critical dynamical response of financial markets. Aftershocks put additional stress on markets, with conceivable dramatic consequences. Such a phenomenon has been shown to be common to most financial assets, both at high and low frequency. Its present-day description relies on an empirical characterization proposed by Omori at the end of 1800 for seismic earthquakes. We point out the limited predictive power in this phenomenological approach and present a stochastic model, based on the scaling symmetry of financial assets, which is potentially capable to predict aftershocks occurrence, given the main shock magnitude. Comparisons with S&P high-frequency data confirm this predictive potential.

  7. Seismotectonic framework of the 2010 February 27 Mw 8.8 Maule, Chile earthquake sequence

    USGS Publications Warehouse

    Hayes, Gavin P.; Bergman, Eric; Johnson, Kendra J.; Benz, Harley M.; Brown, Lucy; Meltzer, Anne S.

    2013-01-01

    After the 2010 Mw 8.8 Maule earthquake, an international collaboration involving teams and instruments from Chile, the US, the UK, France and Germany established the International Maule Aftershock Deployment temporary network over the source region of the event to facilitate detailed, open-access studies of the aftershock sequence. Using data from the first 9-months of this deployment, we have analyzed the detailed spatial distribution of over 2500 well-recorded aftershocks. All earthquakes have been relocated using a hypocentral decomposition algorithm to study the details of and uncertainties in both their relative and absolute locations. We have computed regional moment tensor solutions for the largest of these events to produce a catalogue of 465 mechanisms, and have used all of these data to study the spatial distribution of the aftershock sequence with respect to the Chilean megathrust. We refine models of co-seismic slip distribution of the Maule earthquake, and show how small changes in fault geometries assumed in teleseismic finite fault modelling significantly improve fits to regional GPS data, implying that the accuracy of rapid teleseismic fault models can be substantially improved by consideration of existing fault geometry model databases. We interpret all of these data in an integrated seismotectonic framework for the Maule earthquake rupture and its aftershock sequence, and discuss the relationships between co-seismic rupture and aftershock distributions. While the majority of aftershocks are interplate thrust events located away from regions of maximum co-seismic slip, interesting clusters of aftershocks are identified in the lower plate at both ends of the main shock rupture, implying internal deformation of the slab in response to large slip on the plate boundary interface. We also perform Coulomb stress transfer calculations to compare aftershock locations and mechanisms to static stress changes following the Maule rupture. Without the

  8. Felt reports and intensity assignments for aftershocks and triggered events of the great 1906 California earthquake

    USGS Publications Warehouse

    Meltzner, Aron J.; Wald, David J.

    2002-01-01

    The San Andreas fault is the longest fault in California and one of the longest strikeslip faults in the world, yet little is known about the aftershocks following the most recent great event on the San Andreas, the M 7.8 San Francisco earthquake, on 18 April 1906. This open-file report is a compilation of first-hand accounts (felt reports) describing aftershocks and triggered events of the 1906 earthquake, for the first twenty months of the aftershock sequence (through December 1907). The report includes a chronological catalog. For the larger events, Modified Mercalli intensities (MMIs) have been assigned based on the descriptions judged to be the most reliable.

  9. Seismological evidence of an active footwall shortcut thrust in the Northern Itoigawa-Shizuoka Tectonic Line derived by the aftershock sequence of the 2014 M 6.7 Northern Nagano earthquake

    NASA Astrophysics Data System (ADS)

    Panayotopoulos, Yannis; Hirata, Naoshi; Hashima, Akinori; Iwasaki, Takaya; Sakai, Shin'ichi; Sato, Hiroshi

    2016-06-01

    A destructive M 6.7 earthquake struck Northern Nagano prefecture on November 22, 2014. The main shock occurred on the Kamishiro fault segment of the northern Itoigawa-Shizuoka Tectonic Line (ISTL). We used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between November 18 and November 30, 2014. To estimate hypocenters, we assigned low Vp models to stations within the Northern Fossa Magna (NFM) basin thus accounting for large lateral crustal heterogeneities across the Kamishiro fault. In order to further improve accuracy, the final hypocenter locations were recalculated inside a 3D velocity model using the double-difference method. We used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock. Our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the Kamishiro fault and dips 30°-45° SE, while the deeper part of the source fault corresponds to the downdip portion of the Otari-Nakayama fault, a high angle fault dipping 50°-65° SE that formed during the opening of the NFM basin in the Miocene. Along its surface trace the Otari-Nakayama fault has been inactive during the late Quaternary. We verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half-space model and comparing it to observed surface deformation from satellite interferometry, assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity. Shallowing of the source fault from 50°-65° to 30°-45° in the upper 4 km, in the areas where both surface fault traces are visible, is a result of footwall shortcut thrusting by the Kamishiro fault off the Otari-Nakayama fault.

  10. Simulating Aftershocks for an On Site Inspection (OSI) Exercise

    SciTech Connect

    Sweeney, J. J.; Ford, S. R.

    2015-10-05

    The experience of IFE14 emphasizes the need for a better way to simulate aftershocks during an OSI exercise. The obvious approach is to develop a digital model of aftershocks that can be used either for a real field exercise or for a computer simulation that can be done in an office, for training for example. However, this approach involves consideration of several aspects, such as how and when to introduce waveforms in a way that maximizes the realism of the data and that will be convincing to a savvy, experienced seismic analyst. The purpose of this report is to outline a plan for how this approach can be implemented.

  11. Spatial patterns of aftershocks of shallow focus earthquakes in California and implications for deep focus earthquakes

    USGS Publications Warehouse

    Michael, A.J.

    1989-01-01

    Previous workers have pioneered statistical techniques to study the spatial distribution of aftershocks with respect to the focal mechanism of the main shock. Application of these techniques to deep focus earthquakes failed to show clustering of aftershocks near the nodal planes of the main shocks. To better understand the behaviour of these statistics, this study applies them to the aftershocks of six large shallow focus earthquakes in California (August 6, 1979, Coyote Lake; May 2, 1983, Coalinga; April 24, 1984, Morgan Hill; August 4, 1985, Kettleman Hills; July 8, 1986, North Palm Springs; and October 1, 1987, Whittier Narrows). The large number of aftershocks accurately located by dense local networks allows us to treat these aftershock sequences individually instead of combining them, as was done for the deep earthquakes. The results for individual sequences show significant clustering about the closest nodal plane and the strike direction for five of the sequences and about the presumed fault plane for all six sequences. This implies that the previously developed method does work properly. The reasons for the lack of clustering about main shock nodal planes for deep focus aftershocks are discussed. -from Author

  12. The Iquique earthquake sequence of April 2014: Bayesian modeling accounting for prediction uncertainty

    NASA Astrophysics Data System (ADS)

    Duputel, Z.; Jiang, J.; Jolivet, R.; Simons, M.; Rivera, L.; Ampuero, J.-P.; Riel, B.; Owen, S. E.; Moore, A. W.; Samsonov, S. V.; Ortega Culaciati, F.; Minson, S. E.

    2015-10-01

    The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. On 1 April 2014, this region was struck by a large earthquake following a two week long series of foreshocks. This study combines a wide range of observations, including geodetic, tsunami, and seismic data, to produce a reliable kinematic slip model of the Mw=8.1 main shock and a static slip model of the Mw=7.7 aftershock. We use a novel Bayesian modeling approach that accounts for uncertainty in the Green's functions, both static and dynamic, while avoiding nonphysical regularization. The results reveal a sharp slip zone, more compact than previously thought, located downdip of the foreshock sequence and updip of high-frequency sources inferred by back-projection analysis. Both the main shock and the Mw=7.7 aftershock did not rupture to the trench and left most of the seismic gap unbroken, leaving the possibility of a future large earthquake in the region.

  13. The Iquique earthquake sequence of April 2014: Bayesian modeling accounting for prediction uncertainty

    USGS Publications Warehouse

    Duputel, Zacharie; Jiang, Junle; Jolivet, Romain; Simons, Mark; Rivera, Luis; Ampuero, Jean-Paul; Riel, Bryan; Owen, Susan E; Moore, Angelyn W; Samsonov, Sergey V; Ortega Culaciati, Francisco; Minson, Sarah E.

    2016-01-01

    The subduction zone in northern Chile is a well-identified seismic gap that last ruptured in 1877. On 1 April 2014, this region was struck by a large earthquake following a two week long series of foreshocks. This study combines a wide range of observations, including geodetic, tsunami, and seismic data, to produce a reliable kinematic slip model of the Mw=8.1 main shock and a static slip model of the Mw=7.7 aftershock. We use a novel Bayesian modeling approach that accounts for uncertainty in the Green's functions, both static and dynamic, while avoiding nonphysical regularization. The results reveal a sharp slip zone, more compact than previously thought, located downdip of the foreshock sequence and updip of high-frequency sources inferred by back-projection analysis. Both the main shock and the Mw=7.7 aftershock did not rupture to the trench and left most of the seismic gap unbroken, leaving the possibility of a future large earthquake in the region.

  14. Self-similar aftershock rates

    NASA Astrophysics Data System (ADS)

    Davidsen, Jörn; Baiesi, Marco

    2016-08-01

    In many important systems exhibiting crackling noise—an intermittent avalanchelike relaxation response with power-law and, thus, self-similar distributed event sizes—the "laws" for the rate of activity after large events are not consistent with the overall self-similar behavior expected on theoretical grounds. This is particularly true for the case of seismicity, and a satisfying solution to this paradox has remained outstanding. Here, we propose a generalized description of the aftershock rates which is both self-similar and consistent with all other known self-similar features. Comparing our theoretical predictions with high-resolution earthquake data from Southern California we find excellent agreement, providing particularly clear evidence for a unified description of aftershocks and foreshocks. This may offer an improved framework for time-dependent seismic hazard assessment and earthquake forecasting.

  15. Self-similar aftershock rates.

    PubMed

    Davidsen, Jörn; Baiesi, Marco

    2016-08-01

    In many important systems exhibiting crackling noise-an intermittent avalanchelike relaxation response with power-law and, thus, self-similar distributed event sizes-the "laws" for the rate of activity after large events are not consistent with the overall self-similar behavior expected on theoretical grounds. This is particularly true for the case of seismicity, and a satisfying solution to this paradox has remained outstanding. Here, we propose a generalized description of the aftershock rates which is both self-similar and consistent with all other known self-similar features. Comparing our theoretical predictions with high-resolution earthquake data from Southern California we find excellent agreement, providing particularly clear evidence for a unified description of aftershocks and foreshocks. This may offer an improved framework for time-dependent seismic hazard assessment and earthquake forecasting.

  16. High-resolution spatial and temporal analysis of the aftershock sequence of the 23 August 2011 Mw 5.8 Mineral, Virginia, earthquake

    NASA Astrophysics Data System (ADS)

    Hilfiker, Stephen Glenn

    Low-earth orbit (LEO) contains plasma which can impact satellite charging and radio frequency (RF) communications. Quantifying both the composition and movement of ions in LEO can improve efficiency of the forecasting models that predict the impact plasma will have on satellite communications and accuracy of global positioning satellite measurements. Two instruments known as the Retarding Potential Analyzer (RPA) and the Ion Drift Meter (IDM) have been used in tandem to measure ionospheric properties including ion temperature, velocity, and density. These instruments are costly and occupy large areas on a spacecraft. In recent years, space mission budgets have diminished. This change has driven innovation towards creating new instruments which are compatible with smaller and cheaper satellites yet still yield measurements of comparable quality. This thesis presents the design of a new instrument that encompasses the functionality of both the RPA and IDM, known as the Plasma Velocity Vector Instrument for Small Satellites (PVVISS). PVVISS has compact form factor and low power requirements, making it a viable option for smaller, low cost nano-satellite sized missions. Missions utilizing the PVVISS sensor will allow increased exploration of the ionospheric impact on satellite communications.

  17. Aftershocks illuminate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

    USGS Publications Warehouse

    Horton, Jr., J. Wright; Shah, Anjana K.; McNamara, Daniel E.; Snyder, Stephen L.; Carter, Aina M

    2015-01-01

    Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

  18. RNA sequence analysis using covariance models.

    PubMed Central

    Eddy, S R; Durbin, R

    1994-01-01

    We describe a general approach to several RNA sequence analysis problems using probabilistic models that flexibly describe the secondary structure and primary sequence consensus of an RNA sequence family. We call these models 'covariance models'. A covariance model of tRNA sequences is an extremely sensitive and discriminative tool for searching for additional tRNAs and tRNA-related sequences in sequence databases. A model can be built automatically from an existing sequence alignment. We also describe an algorithm for learning a model and hence a consensus secondary structure from initially unaligned example sequences and no prior structural information. Models trained on unaligned tRNA examples correctly predict tRNA secondary structure and produce high-quality multiple alignments. The approach may be applied to any family of small RNA sequences. Images PMID:8029015

  19. Assessment of Quantitative Aftershock Productivity Potential in Mining-Induced Seismicity

    NASA Astrophysics Data System (ADS)

    Kozłowska, Maria; Orlecka-Sikora, Beata

    2017-03-01

    Strong mining-induced earthquakes exhibit various aftershock patterns. The aftershock productivity is governed by the geomechanical properties of rock in the seismogenic zone, mining-induced stress and coseismic stress changes related to the main shock's magnitude, source geometry and focal mechanism. In order to assess the quantitative aftershock productivity potential in the mining environment we apply a forecast model based on natural seismicity properties, namely constant tectonic loading and the Gutenberg-Richter frequency-magnitude distribution. Although previous studies proved that mining-induced seismicity does not obey the simple power law, here we apply it as an approximation of seismicity distribution to resolve the number of aftershocks, not considering their magnitudes. The model used forecasts the aftershock productivity based on the background seismicity level estimated from an average seismic moment released per earthquake and static stress changes caused by a main shock. Thus it accounts only for aftershocks directly triggered by coseismic process. In this study we use data from three different mines, Mponeng (South Africa), Rudna and Bobrek (Poland), representing different geology, exploitation methods and aftershock patterns. Each studied case is treated with individual parameterization adjusted to the data specifics. We propose the modification of the original model, i.e. including the non-uniformity of M 0, resulting from spatial correlation of mining-induced seismicity with exploitation. The results show that, even when simplified seismicity distribution parameters are applied, the modified model predicts the number of aftershocks for each analyzed case well and accounts for variations between these values. Such results are thus another example showing that coseismic processes of mining-induced seismicity reflect features of natural seismicity and that similar models can be applied to study the aftershock rate in both the natural and the

  20. Assessment of Quantitative Aftershock Productivity Potential in Mining-Induced Seismicity

    NASA Astrophysics Data System (ADS)

    Kozłowska, Maria; Orlecka-Sikora, Beata

    2016-12-01

    Strong mining-induced earthquakes exhibit various aftershock patterns. The aftershock productivity is governed by the geomechanical properties of rock in the seismogenic zone, mining-induced stress and coseismic stress changes related to the main shock's magnitude, source geometry and focal mechanism. In order to assess the quantitative aftershock productivity potential in the mining environment we apply a forecast model based on natural seismicity properties, namely constant tectonic loading and the Gutenberg-Richter frequency-magnitude distribution. Although previous studies proved that mining-induced seismicity does not obey the simple power law, here we apply it as an approximation of seismicity distribution to resolve the number of aftershocks, not considering their magnitudes. The model used forecasts the aftershock productivity based on the background seismicity level estimated from an average seismic moment released per earthquake and static stress changes caused by a main shock. Thus it accounts only for aftershocks directly triggered by coseismic process. In this study we use data from three different mines, Mponeng (South Africa), Rudna and Bobrek (Poland), representing different geology, exploitation methods and aftershock patterns. Each studied case is treated with individual parameterization adjusted to the data specifics. We propose the modification of the original model, i.e. including the non-uniformity of M 0, resulting from spatial correlation of mining-induced seismicity with exploitation. The results show that, even when simplified seismicity distribution parameters are applied, the modified model predicts the number of aftershocks for each analyzed case well and accounts for variations between these values. Such results are thus another example showing that coseismic processes of mining-induced seismicity reflect features of natural seismicity and that similar models can be applied to study the aftershock rate in both the natural and the

  1. Spatiotemporal Aftershock Complexity in the November 8th 2011, Prague, OK Earthquake: Insights into the Role of Damage Zones in the Seismic Cycle

    NASA Astrophysics Data System (ADS)

    Savage, H. M.; Keranen, K. M.; Schaff, D. P.; Dieck, C. C. M.

    2014-12-01

    Although most faults are surrounded by a halo of fractured rock known as a damage zone, it is not clear what role damage zones play during the seismic cycle on mature faults. Here, we present a superbly-located foreshock-mainshock-aftershock sequence surrounding the November 8, M5 Prague Oklahoma earthquake, which demonstrates most aftershocks are located within the damage zone surrounding the fault. The 2011 Prague, Oklahoma sequence included three M5+ earthquakes along three different faults over a three-day period. The November 8th event was third in the sequence and captured with an array of nine seismometers with ~2 km spacing, allowing for precise event location. We located more than 1000 foreshocks and aftershocks within a 14 hour time window, and relocated these aftershocks using waveform cross correlation and HypoDD. Because of the location precision, we can use these events to investigate spatial and temporal complexity of the foreshock and aftershock sequences. First, we compare the aftershock distribution to fracture distributions within damage zones surrounding faults. The aftershock sequence localizes to a reasonable damage zone thickness given the rupture length of the event, according to previously documented scaling between fault length and damage zone thickness. Furthermore, the aftershock density is constant within the fault zone, but falls off precipitously outside of the damage zone. Most aftershocks in this sequence occur within the first hour after the mainshock, and there is some indication of temporal migration of aftershocks away from the fault. Finally, foreshock activity along this fault was limited to the intersection with the fault that had hosted a M5.7 earthquake two days prior. Because this earthquake is potentially linked to fluid waste disposal, we interpret our results in terms of hydraulic pressure changes during the foreshock-mainshock-aftershock sequence.

  2. Delayed Triggering of Early Aftershocks by Multiple Waves Circling the Earth

    NASA Astrophysics Data System (ADS)

    Sullivan, B.; Peng, Z.

    2011-12-01

    It is well known that direct surface waves of large earthquakes are capable of triggering shallow earthquakes and deep tremor at long-range distances. Recent studies have shown that multiple surface waves circling the earth could also remotely trigger microearthquakes [Peng et al., 2011]. However, it is still not clear whether multiple surface waves returning back to the mainshock epicenters could also trigger/modulate aftershock activities. Here we conduct a study to search for evidence of such triggering by systematically examining aftershock activities of 20 magnitude-8-or-higher earthquakes since 1990 that are capable of producing surface waves circling the globe repeatedly. We compute the magnitude of completeness for each sequence, and stack all the sequences together to compute the seismicity and moment rates by sliding data windows. The sequences are also shuffled randomly and these rates are compared to the actual data as well as synthetic aftershock sequences to estimate the statistical significance of the results. We also compare them with varying stacks of magnitude 7-8 earthquakes to better understand the possible biases that could be introduced by our rate calculation method. Our preliminary results suggest that there is some moderate increase of early aftershock activity after a few hours when the surface waves return to the epicentral region. However, we could not completely rule out the possibility that such an increase is purely due to random fluctuations of aftershocks or caused by missing aftershocks in the first few hours after the mainshock. We plan to examine continuous waveform data of selected sequences to obtain a better understanding of the multiple surface waves and aftershock activity.

  3. Aftershock decay, productivity, and stress rates in Hawaii: Indicators of temperature and stress from magma sources

    USGS Publications Warehouse

    Klein, Fred W.; Wright, Tom; Nakata, Jennifer

    2006-01-01

    We examined dozens of aftershock sequences in Hawaii in terms of Gutenberg-Richter and modified Omori law parameters. We studied p, the rate of aftershock decay; Ap, the aftershock productivity, defined as the observed divided by the expected number of aftershocks; and c, the time delay when aftershock rates begin to fall. We found that for earthquakes shallower than 20 km, p values >1.2 are near active magma centers. We associate this high decay rate with higher temperatures and faster stress relaxation near magma reservoirs. Deep earthquakes near Kilauea's inferred magma transport path show a range of p values, suggesting the absence of a large, deep magma reservoir. Aftershock productivity is >4.0 for flank earthquakes known to be triggered by intrusions but is normal (0.25 to 4.0) for isolated main shocks. We infer that continuing, post-main shock stress from the intrusion adds to the main shock's stress step and causes higher Ap. High Ap in other zones suggests less obvious intrusions and pulsing magma pressure near Kilauea's feeding conduit. We calculate stress rates and stress rate changes from pre-main shock and aftershock rates. Stress rate increased after many intrusions but decreased after large M7–8 earthquakes. Stress rates are highest in the seismically active volcano flanks and lowest in areas far from volcanic centers. We found sequences triggered by intrusions tend to have high Ap, high (>0.10 day) c values, a stress rate increase, and sometimes a peak in aftershock rate hours after the main shock. We interpret these values as indicating continuing intrusive stress after the main shock.

  4. Prediction of seismic moment release of aftershocks by a kinetic law

    NASA Astrophysics Data System (ADS)

    Daminelli, Rosastella; Marcellini, Alberto

    2013-04-01

    We modelled the temporal behaviour of the cumulative seismic moment releases of aftershock sequences by a kinetic approach of the fracture mechanism. This approach considers that the relation between applied stress and time-to-break is conditioned by two competing phenomena occurring in the fracture zone: the breakage of unbroken elements and the reformation of broken elements. With respect to the familiar log-linear relation between stress and fracture time of static fatigue, the present approach also considers the damage evolution of the material during the fracture process. From a math point of view it means a modification of the log-linear relation by the introduction in the equation of a new factor that represents the fraction of integrity of the materials: the result is a better fit of experimental data. The aftershock model we derived has been applied to seven aftershock sequences of Californian earthquakes selected from the SCEC database: the mainshocks range from M=5.45 to M=7.3. We considered a total time interval of 120 days following the mainshock, but for Whittier Narrows (110 days), with the same magnitude threshold (M=1.8) for all the sequences. The total number of events considered ranges from the 470 of Whittier Narrows (October 1, 1987) to the 12573 of Landers (June 28, 1992). To check the predictive validity of the model we analysed the forecast of the cumulative seismic moment release as a function of time: we defined ? as the elapsed time, since the mainshock, required to evaluate the costants of the equation sufficient to obtain predictions of the cumulative seismic moment with maximum error of 3 days for the whole remaining sequence. We obtained ? = 2.8 days for Whittier Narrows, ? = 3 days for Landers, ? = 15 hours for Northridge (January 17, 1994), ? = 9 days for North Palm Springs (July 8, 1986) and ? = 6 days for Hector Mine (October 16, 1999). Unfortunately two sequences, Ridgecrest (September 20, 1995) and Oceanside (July 13, 1986

  5. Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century

    USGS Publications Warehouse

    Klein, F.W.; Wright, Tim

    2008-01-01

    The remarkable catalog of Hawaiian earthquakes going back to the 1820s is based on missionary diaries, newspaper accounts, and instrumental records and spans the great M7.9 Kau earthquake of April 1868 and its aftershock sequence. The earthquake record since 1868 defines a smooth curve complete to M5.2 of the declining rate into the 21st century, after five short volcanic swarms are removed. A single aftershock curve fits the earthquake record, even with numerous M6 and 7 main shocks and eruptions. The timing of some moderate earthquakes may be controlled by magmatic stresses, but their overall long-term rate reflects one of aftershocks of the Kau earthquake. The 1868 earthquake is, therefore, the largest and most controlling stress event in the 19th and 20th centuries. We fit both the modified Omori (power law) and stretched exponential (SE) functions to the earthquakes. We found that the modified Omori law is a good fit to the M ??? 5.2 earthquake rate for the first 10 years or so and the more rapidly declining SE function fits better thereafter, as supported by three statistical tests. The switch to exponential decay suggests that a possible change in aftershock physics may occur from rate and state fault friction, with no change in the stress rate, to viscoelastic stress relaxation. The 61-year exponential decay constant is at the upper end of the range of geodetic relaxation times seen after other global earthquakes. Modeling deformation in Hawaii is beyond the scope of this paper, but a simple interpretation of the decay suggests an effective viscosity of 1019 to 1020 Pa s pertains in the volcanic spreading of Hawaii's flanks. The rapid decline in earthquake rate poses questions for seismic hazard estimates in an area that is cited as one of the most hazardous in the United States.

  6. Aftershock triggering by complete Coulomb stress changes

    USGS Publications Warehouse

    Kilb, Debi; Gomberg, J.; Bodin, P.

    2002-01-01

    We examine the correlation between seismicity rate change following the 1992, M7.3, Landers, California, earthquake and characteristics of the complete Coulomb failure stress (CFS) changes (??CFS(t)) that this earthquake generated. At close distances the time-varying "dynamic" portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement. The permanent "static" portion (??CFS) depends only on the final coseismic displacement. ??CFS diminishes much more rapidly with distance than the transient, dynamic stress changes. A common interpretation of the strong correlation between ??CFS and aftershocks is that load changes can advance or delay failure. Stress changes may also promote failure by physically altering properties of the fault or its environs. Because it is transient, ??CFS(t) can alter the failure rate only by the latter means. We calculate both ??CFS and the maximum positive value of ??CFS(t) (peak ??CFS(t)) using a reflectivity program. Input parameters are constrained by modeling Landers displacement seismograms. We quantify the correlation between maps of seismicity rate changes and maps of modeled ??CFS and peak ??CFS(t) and find agreement for both models. However, rupture directivity, which does not affect ??CFS, creates larger peak ??CFS(t) values northwest of the main shock. This asymmetry is also observed in seismicity rate changes but not in ??CFS. This result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed.

  7. A Quantitative Test for the Spatial Relationship Between Aftershock Distributions and Mainshock Rupture Properties

    NASA Astrophysics Data System (ADS)

    Woessner, J.; Ripperger, J.; Mai, M. P.; Wiemer, S.

    2004-12-01

    Correlating the properties of the mainshock rupture with the location of corresponding aftershocks may provide insight into the relationship between mainshock-induced static stress changes and aftershock occurrence. In this study, we develop a rigorous statistical test to quantify the spatial pattern of aftershock locations with the corresponding distributions of coseismic slip and stress-drop. Well-located aftershock hypocenters are projected onto the mainshock fault plane and coseismic slip and stress drop values are interpolated to their respective location. The null hypothesis H0 for the applied test statistic is: Aftershock hypocenters are randomly distributed on the mainshock fault plane and are not correlated with mainshock properties. Because we want to maintain spatial earthquake clustering as one of the important observed features of seismicity, we synthesize slip distributions using a random spatial field model from which we then compute the respective stress-drop distributions. For each simulation of earthquake slip, we compute the test statistic for the slip and stress-drop distribution, testing whether or not an apparent correlation between mainshock properties and aftershock locations exists. Uncertainties in the aftershock locations are accounted for by simulating a thousand catalogues for which we randomize the location of the aftershocks within their given location error bounds. We then determine the number of aftershocks in low-slip or negative stress-drop regions for simulated slip distributions, and compare those to the measurements obtained for finite-source slip inversions. We apply the test to crustal earthquakes in California and Japan. If possible, we use different source models and earthquake catalogues with varying accuracy to investigate the dependence of the test results on, for example, the location uncertainties of aftershocks. Contrary to the visual impression, we find that for some strike-slip earthquakes or segments of the

  8. Foreshocks and aftershocks of Pisagua 2014 earthquake: time and space evolution of megathrust event.

    NASA Astrophysics Data System (ADS)

    Fuenzalida Velasco, Amaya; Rietbrock, Andreas; Wollam, Jack; Thomas, Reece; de Lima Neto, Oscar; Tavera, Hernando; Garth, Thomas; Ruiz, Sergio

    2016-04-01

    The 2014 Pisagua earthquake of magnitude 8.2 is the first case in Chile where a foreshock sequence was clearly recorded by a local network, as well all the complete sequence including the mainshock and its aftershocks. The seismicity of the last year before the mainshock include numerous clusters close to the epicentral zone (Ruiz et al; 2014) but it was on 16th March that this activity became stronger with the Mw 6.7 precursory event taking place in front of Iquique coast at 12 km depth. The Pisagua earthquake arrived on 1st April 2015 breaking almost 120 km N-S and two days after a 7.6 aftershock occurred in the south of the rupture, enlarging the zone affected by this sequence. In this work, we analyse the foreshocks and aftershock sequence of Pisagua earthquake, from the spatial and time evolution for a total of 15.764 events that were recorded from the 1st March to 31th May 2015. This event catalogue was obtained from the automatic analyse of seismic raw data of more than 50 stations installed in the north of Chile and the south of Peru. We used the STA/LTA algorithm for the detection of P and S arrival times on the vertical components and then a method of back propagation in a 1D velocity model for the event association and preliminary location of its hypocenters following the algorithm outlined by Rietbrock et al. (2012). These results were then improved by locating with NonLinLoc software using a regional velocity model. We selected the larger events to analyse its moment tensor solution by a full waveform inversion using ISOLA software. In order to understand the process of nucleation and propagation of the Pisagua earthquake, we also analysed the evolution in time of the seismicity of the three months of data. The zone where the precursory events took place was strongly activated two weeks before the mainshock and remained very active until the end of the analysed period with an important quantity of the seismicity located in the upper plate and having

  9. Complex faulting associated with the 22 December 2003 Mw 6.5 San Simeon California, earthquake, aftershocks and postseismic surface deformation

    USGS Publications Warehouse

    McLaren, M.K.; Hardebeck, J.L.; van der Elst, N.; Unruh, J.R.; Bawden, G.W.; Blair, J.L.

    2008-01-01

    We use data from two seismic networks and satellite interferometric synthetic aperture radar (InSAR) imagery to characterize the 22 December 2003 Mw 6.5 San Simeon earthquake sequence. Absolute locations for the mainshock and nearly 10,000 aftershocks were determined using a new three-dimensional (3D) seismic velocity model; relative locations were obtained using double difference. The mainshock location found using the 3D velocity model is 35.704?? N, 121.096?? W at a depth of 9.7 ?? 0.7 km. The aftershocks concentrate at the northwest and southeast parts of the aftershock zone, between the mapped traces of the Oceanic and Nacimiento fault zones. The northwest end of the mainshock rupture, as defined by the aftershocks, projects from the mainshock hypocenter to the surface a few kilometers west of the mapped trace of the Oceanic fault, near the Santa Lucia Range front and the > 5 mm postseismic InSAR imagery contour. The Oceanic fault in this area, as mapped by Hall (1991), is therefore probably a second-order synthetic thrust or reverse fault that splays upward from the main seismogenic fault at depth. The southeast end of the rupture projects closer to the mapped Oceanic fault trace, suggesting much of the slip was along this fault, or at a minimum is accommodating much of the postseismic deformation. InSAR imagery shows ???72 mm of postseismic uplift in the vicinity of maximum coseismic slip in the central section of the rupture, and ???48 and ???45 mm at the northwest and southeast end of the aftershock zone, respectively. From these observations, we model a ???30-km-long northwest-trending northeast-dipping mainshock rupture surface - called the mainthrust - which is likely the Oceanic fault at depth, a ???10-km-long southwest-dipping backthrust parallel to the mainthrust near the hypocenter, several smaller southwest-dipping structures in the southeast, and perhaps additional northeast-dipping or subvertical structures southeast of the mainshock plane

  10. The Use of Explosion Aftershock Probabilities for Planning and Deployment of Seismic Aftershock Monitoring System for an On-site Inspection

    NASA Astrophysics Data System (ADS)

    Labak, P.; Ford, S. R.; Sweeney, J. J.; Smith, A. T.; Spivak, A.

    2011-12-01

    One of four elements of CTBT verification regime is On-site inspection (OSI). Since the sole purpose of an OSI shall be to clarify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out, inspection activities can be conducted and techniques used in order to collect facts to support findings provided in inspection reports. Passive seismological monitoring, realized by the seismic aftershock monitoring (SAMS) is one of the treaty allowed techniques during an OSI. Effective planning and deployment of SAMS during the early stages of an OSI is required due to the nature of possible events recorded and due to the treaty related constrains on size of inspection area, size of inspection team and length of an inspection. A method, which may help in planning the SAMS deployment is presented. An estimate of aftershock activity due to a theoretical underground nuclear explosion is produced using a simple aftershock rate model (Ford and Walter, 2010). The model is developed with data from the Nevada Test Site and Semipalatinsk Test Site, which we take to represent soft- and hard-rock testing environments, respectively. Estimates of expected magnitude and number of aftershocks are calculated using the models for different testing and inspection scenarios. These estimates can help to plan the SAMS deployment for an OSI by giving a probabilistic assessment of potential aftershocks in the Inspection Area (IA). The aftershock assessment combined with an estimate of the background seismicity in the IA and an empirically-derived map of threshold magnitude for the SAMS network could aid the OSI team in reporting. We tested the hard-rock model to a scenario similar to the 2008 Integrated Field Exercise 2008 deployment in Kazakhstan and produce an estimate of possible recorded aftershock activity.

  11. Afterslip and Aftershocks Triggered by Moderate Events on the San-Jacinto Fault

    NASA Astrophysics Data System (ADS)

    Inbal, A.; Ampuero, J. P.; Avouac, J.

    2013-12-01

    The San-Jacinto Fault (SJF) is one of the most active faults in southern California, which together with the southern San-Andreas Fault accommodates a large fraction of the total accumulated strain within the plate boundary. Seismicity along the SJF is distributed over several fault segments with distinct spatio-temporal characteristics. One of these segments, also known as the Anza seismic gap, is a 20 km long strand of the fault almost devoid of seismicity. Several M>6 events occurred along the SJF over the past 100 years, none of which is thought to have ruptured the gap (Sanders and Kanamori, 1984). In recent years, four M4-5 events occurred south of the gap. Despite their moderate magnitudes, these earthquakes triggered rich aftershock sequences and pronounced post-seismic slip. This complex pattern of seismic and aseismic deformation along the SJF has important implications for seismic hazard estimation, and may also entail clues about the physical processes that govern fault slip at depth. Here we perform a joint inversion of the aftershocks and geodetic data sets in order to recover the evolution of post-seismic slip on the SJF. We analyze continuous strain records from PBO borehole instruments installed within a few kilometres from the trace of the SJF. These sites recorded an abrupt, weeks long increase in strain rate following three M4-5 events that occurred in 2005, 2010, and 2013. A similar, yet shorter response was observed following the 2010 M7.2 El Mayor-Cucapah earthquake. These episodes were accompanied by increased seismicity rates which decayed to the background level according to the modified Omori law. The aftershocks data set is used to improve the limited sensitivity of geodetic data sets to deep fault slip. Our approach is based on the Dieterich's (1994) aftershock model for the response of a fault governed by rate-and-state friction to a stress perturbation. Based on this formulation, we are able to infer the stress time-histories of

  12. Stress history controls the spatial pattern of aftershocks: case studies from strike-slip earthquakes

    NASA Astrophysics Data System (ADS)

    Utkucu, Murat; Durmuş, Hatice; Nalbant, Süleyman

    2016-09-01

    Earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates with the following seismicity. Here we have documented five cases of the mainshock-aftershock sequences generated by the strike-slip faults from different tectonic environments of world in order to demonstrate that the stress changes resulting from large preceding earthquakes decades before effect spatial distribution of the aftershocks of the current mainshocks. The studied mainshock-aftershock sequences are the 15 October 1979 Imperial Valley earthquake (Mw = 6.4) in southern California, the 27 November 1979 Khuli-Boniabad (Mw = 7.1), the 10 May 1997 Qa'enat (Mw = 7.2) and the 31 March 2006 Silakhor (Mw = 6.1) earthquakes in Iran and the 13 March 1992 Erzincan earthquake (Mw = 6.7) in Turkey. In the literature, we have been able to find only these mainshocks that are mainly characterized by dense and strong aftershock activities along and beyond the one end of their ruptures while rare aftershock occurrences with relatively lower magnitude reported for the other end of their ruptures. It is shown that the stress changes resulted from earlier mainshock(s) that are close in both time and space might be the reason behind the observed aftershock patterns. The largest aftershocks of the mainshocks studied tend to occur inside the stress-increased lobes that were also stressed by the background earthquakes and not to occur inside the stress-increased lobes that fall into the stress shadow of the background earthquakes. We suggest that the stress shadows of the previous mainshocks may persist in the crust for decades to suppress aftershock distribution of the current mainshocks. Considering active researches about use of the Coulomb stress change maps as a practical tool to forecast spatial distribution of the upcoming aftershocks for earthquake risk mitigation purposes in near-real time, it is further suggested that

  13. Sensitivity study of forecasted aftershock seismicity based on Coulomb stress calculation and rate- and state-dependent frictional response

    NASA Astrophysics Data System (ADS)

    Cocco, M.; Hainzl, S.; Catalli, F.; Enescu, B.; Lombardi, A. M.; Woessner, J.

    2010-05-01

    We use the Dieterich (1994) physics-based approach to simulate the spatiotemporal evolution of seismicity caused by stress changes applied to an infinite population of nucleating patches modeled through a rate- and state-dependent friction law. According to this model, seismicity rate changes depend on the amplitude of stress perturbation, the physical constitutive properties of faults (represented by the parameter Aσ), the stressing rate, and the background seismicity rate of the study area. In order to apply this model in a predictive manner, we need to understand the impact of physical model parameters and the correlations between them. First, we discuss different definitions of the reference seismicity rate and show their impact on the computed rate of earthquake production for the 1992 Landers earthquake sequence as a case study. Furthermore, we demonstrate that all model parameters are strongly correlated for physical and statistical reasons. We discuss this correlation, emphasizing that the estimations of the background seismicity rate, stressing rate, and Aσ are strongly correlated to reproduce the observed aftershock productivity. Our analytically derived relation demonstrates the impact of these model parameters on the Omori-like aftershock decay: the c value and the productivity of the Omori law, implying a p value smaller than or equal to 1. Finally, we discuss an optimal strategy to constrain model parameters for near-real-time forecasts.

  14. The enigma of the Arthur's Pass, New Zealand, earthquake 1. Reconciling a variety of data for an unusual earthquake sequence

    USGS Publications Warehouse

    Abercrombie, R.E.; Webb, T.H.; Robinson, R.; McGinty, P.J.; Mori, J.J.; Beavan, R.J.

    2000-01-01

    The 1994 Arthur's Pass earthquake (Mw6.7) is the largest in a recent sequence of earthquakes in the central South Island, New Zealand. No surface rupture was observed the aftershock distribution was complex, and routine methods of obtaining the faulting orientation of this earthquake proved contradictory. We use a range of data and techniques to obtain our preferred solution, which has a centroid depth of 5 km, Mo=1.3??1019 N m, and a strike, dip, and rake of 221??, 47??, 112??, respectively. Discrepancies between this solution and the Harvard centroid moment tensor, together with the Global Positioning System (GPS) observations and unusual aftershock distribution, suggest that the rupture may not have occurred on a planar fault. A second, strike slip, subevent on a more northerly striking plane is suggested by these data but neither the body wave modeling nor regional broadband recordings show any complexity or late subevents. We relocate the aftershocks using both one-dimensional and three-dimensional velocity inversions. The depth range of the aftershocks (1-10 km) agrees well with the preferred mainshock centroid depth. The aftershocks near the hypocenter suggest a structure dipping toward the NW, which we interpret to be the mainshock fault plane. This structure and the Harper fault, ???15 km to the south appear to have acted as boundaries to the extensive aftershock zone trending NNW-SSE Most of the ML???5 aftershocks, including the two largest (ML6.1 and ML5.7), clustered near the Harper fault and have strike slip mechanisms consistent with motion on this fault and its conjugates. Forward modeling of the GPS data suggests that a reverse slip mainshock, combined with strike slip aftershock faulting in the south, is able to match the observed displacements. The occurrence of this earthquake sequence implies that the level of seismic hazard in the central South Island is greater than previous estimates. Copyright 2000 by the American Geophysical Union.

  15. Constraints on recent earthquake source parameters, fault geometry and aftershock characteristics in Oklahoma

    NASA Astrophysics Data System (ADS)

    McNamara, D. E.; Benz, H.; Herrmann, R. B.; Bergman, E. A.; McMahon, N. D.; Aster, R. C.

    2014-12-01

    In late 2009, the seismicity of Oklahoma increased dramatically. The largest of these earthquakes was a series of three damaging events (Mw 4.8, 5.6, 4.8) that occurred over a span of four days in November 2011 near the town of Prague in central Oklahoma. Studies suggest that these earthquakes were induced by reactivation of the Wilzetta fault due to the disposal of waste water from hydraulic fracturing ("fracking") and other oil and gas activities. The Wilzetta fault is a northeast trending vertical strike-slip fault that is a well known structural trap for oil and gas. Since the November 2011 Prague sequence, thousands of small to moderate (M2-M4) earthquakes have occurred throughout central Oklahoma. The most active regions are located near the towns of Stillwater and Medford in north-central Oklahoma, and Guthrie, Langston and Jones near Oklahoma City. The USGS, in collaboration with the Oklahoma Geological Survey and the University of Oklahoma, has responded by deploying numerous temporary seismic stations in the region in order to record the vigorous aftershock sequences. In this study we use data from the temporary seismic stations to re-locate all Oklahoma earthquakes in the USGS National Earthquake Information Center catalog using a multiple-event approach known as hypo-centroidal decomposition that locates earthquakes with decreased uncertainty relative to one another. Modeling from this study allows us to constrain the detailed geometry of the reactivated faults, as well as source parameters (focal mechanisms, stress drop, rupture length) for the larger earthquakes. Preliminary results from the November 2011 Prague sequence suggest that subsurface rupture lengths of the largest earthquakes are anomalously long with very low stress drop. We also observe very high Q (~1000 at 1 Hz) that explains the large felt areas and we find relatively low b-value and a rapid decay of aftershocks.

  16. High-Resolution Low Power, Intergrated Aftershock and Microzonation System

    NASA Astrophysics Data System (ADS)

    Zimakov, L.; Passmore, P.

    2012-04-01

    Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system. The detailed specifications and performance are presented and discussed

  17. Sequence modelling and an extensible data model for genomic database

    SciTech Connect

    Li, Peter Wei-Der |

    1992-01-01

    The Human Genome Project (HGP) plans to sequence the human genome by the beginning of the next century. It will generate DNA sequences of more than 10 billion bases and complex marker sequences (maps) of more than 100 million markers. All of these information will be stored in database management systems (DBMSs). However, existing data models do not have the abstraction mechanism for modelling sequences and existing DBMS`s do not have operations for complex sequences. This work addresses the problem of sequence modelling in the context of the HGP and the more general problem of an extensible object data model that can incorporate the sequence model as well as existing and future data constructs and operators. First, we proposed a general sequence model that is application and implementation independent. This model is used to capture the sequence information found in the HGP at the conceptual level. In addition, abstract and biological sequence operators are defined for manipulating the modelled sequences. Second, we combined many features of semantic and object oriented data models into an extensible framework, which we called the ``Extensible Object Model``, to address the need of a modelling framework for incorporating the sequence data model with other types of data constructs and operators. This framework is based on the conceptual separation between constructors and constraints. We then used this modelling framework to integrate the constructs for the conceptual sequence model. The Extensible Object Model is also defined with a graphical representation, which is useful as a tool for database designers. Finally, we defined a query language to support this model and implement the query processor to demonstrate the feasibility of the extensible framework and the usefulness of the conceptual sequence model.

  18. Sequence modelling and an extensible data model for genomic database

    SciTech Connect

    Li, Peter Wei-Der Lawrence Berkeley Lab., CA )

    1992-01-01

    The Human Genome Project (HGP) plans to sequence the human genome by the beginning of the next century. It will generate DNA sequences of more than 10 billion bases and complex marker sequences (maps) of more than 100 million markers. All of these information will be stored in database management systems (DBMSs). However, existing data models do not have the abstraction mechanism for modelling sequences and existing DBMS's do not have operations for complex sequences. This work addresses the problem of sequence modelling in the context of the HGP and the more general problem of an extensible object data model that can incorporate the sequence model as well as existing and future data constructs and operators. First, we proposed a general sequence model that is application and implementation independent. This model is used to capture the sequence information found in the HGP at the conceptual level. In addition, abstract and biological sequence operators are defined for manipulating the modelled sequences. Second, we combined many features of semantic and object oriented data models into an extensible framework, which we called the Extensible Object Model'', to address the need of a modelling framework for incorporating the sequence data model with other types of data constructs and operators. This framework is based on the conceptual separation between constructors and constraints. We then used this modelling framework to integrate the constructs for the conceptual sequence model. The Extensible Object Model is also defined with a graphical representation, which is useful as a tool for database designers. Finally, we defined a query language to support this model and implement the query processor to demonstrate the feasibility of the extensible framework and the usefulness of the conceptual sequence model.

  19. Tests of remote aftershock triggering by small mainshocks using Taiwan's earthquake catalog

    NASA Astrophysics Data System (ADS)

    Peng, W.; Toda, S.

    2014-12-01

    To understand earthquake interaction and forecast time-dependent seismic hazard, it is essential to evaluate which stress transfer, static or dynamic, plays a major role to trigger aftershocks and subsequent mainshocks. Felzer and Brodsky focused on small mainshocks (2≤M<3) and their aftershocks, and then argued that only dynamic stress change brings earthquake-to-earthquake triggering, whereas Richards-Dingers et al. (2010) claimed that those selected small mainshock-aftershock pairs were not earthquake-to-earthquake triggering but simultaneous occurrence of independent aftershocks following a larger earthquake or during a significant swarm sequence. We test those hypotheses using Taiwan's earthquake catalog by taking the advantage of lacking any larger event and the absence of significant seismic swarm typically seen with active volcano. Using Felzer and Brodsky's method and their standard parameters, we only found 14 mainshock-aftershock pairs occurred within 20 km distance in Taiwan's catalog from 1994 to 2010. Although Taiwan's catalog has similar number of earthquakes as California's, the number of pairs is about 10% of the California catalog. It may indicate the effect of no large earthquakes and no significant seismic swarm in the catalog. To fully understand the properties in the Taiwan's catalog, we loosened the screening parameters to earn more pairs and then found a linear aftershock density with a power law decay of -1.12±0.38 that is very similar to the one in Felzer and Brodsky. However, none of those mainshock-aftershock pairs were associated with a M7 rupture event or M6 events. To find what mechanism controlled the aftershock density triggered by small mainshocks in Taiwan, we randomized earthquake magnitude and location. We then found that those density decay in a short time period is more like a randomized behavior than mainshock-aftershock triggering. Moreover, 5 out of 6 pairs were found in a swarm-like temporal seismicity rate increase

  20. Scaling Relations Between Mainshock Source Parameters and Aftershock Distributions for Use in Aftershock Forecasting

    NASA Astrophysics Data System (ADS)

    Donovan, J.; Jordan, T. H.

    2010-12-01

    Aftershocks are often used to delineate the mainshock rupture zone retrospectively. In aftershock forecasting on the other hand, the problem is to use mainshock rupture area to determine the aftershock zone prospectively. The procedures for this type of prediction are not as well developed and have been restricted to simple parameterizations such as the Utsu-Seki (1955) scaling relation between mainshock energy and aftershock area (Ogata and Zhueng, 2006). With a focus on improving current forecasting methods, we investigate the relationship between spatial source parameters that can be rapidly computed (spatial centroid and characteristic dimensions) and corresponding spatial measures of the aftershock distribution. For a set of about 30 large events, we either extracted source parameters from the McGuire et al (2002) finite moment tensor (FMT) catalog, or computed them from the online SRCMOD database (Mai, 2004). We identified aftershocks with windowing and scale-free methods, and computed both L1 and L2 measures of their distributions. Our comparisons produce scaling relations among the characteristic dimensions that can be used to initiate aftershock forecasts. By using rapidly-determined source parameters, we can decrease the forecasting latency and thus improve the probability gain of the forecasting methods.

  1. Using aftershocks to Image the Subducting Pacific Plate in a Region of Deep Slow Slip, Hikurangi Margin, New Zealand

    NASA Astrophysics Data System (ADS)

    Jacobs, K. M.; Hirschberg, H.; Louie, J. N.; Savage, M. K.; Bannister, S. C.

    2014-12-01

    We present seismic migrations using aftershocks of two M>6 earthquakes as sources. The Southern Cook Strait earthquake sequence, beginning on 19 July 2013, included the 21 July M=6.5 and 16 August M=6.6 2013 earthquakes, which were the largest shallow earthquakes to strike the Wellington region since 1942. Following the two largest earthquakes we began the Seddon Earthquake Aftershock Structural Investigation (SEASI) and deployed a line of 21 seismometers stretching approximately 400 km along the strike of the Hikurangi subduction zone in order to use aftershocks to illuminate the structure of the subducted Pacific slab. The SEASI line ties into the SAHKE line, which was an array of up to 900 seismometers that recorded air gun and explosion shots in deployments from 2009-2011. The SAHKE project characterized the structures perpendicular to the strike of the subduction zone. Our results use the SAHKE line as a starting point and look for strike-parallel variations in the depth of the Moho and other structures. Previous studies have suggested potential changes along strike in this region, and deep slow slip events (> 35 km) are also observed north of Wellington, further indicating that variation in properties exists along slab strike. We have used 246 M > 3 earthquakes that occurred from September 2013 through January 2014 to create common receiver gathers. Multicomponent prestack depth migration of these receiver gathers, with operator antialiasing control and prestack coherency filtering, produces reflectivity sections using a 1-D velocity model derived from the SAHKE project. Relocation of aftershocks of the Seddon earthquakes using the deployment of a temporary array by New Zealand GeoNet facilitates the migration. An initial P-P migration shows a north-dipping reflector at 15-25 km depth under the earthquake sequence, and suggests the Moho at 20-25 km depth. From Wellington, a reflector dips very gently south from 25-35 km depth, which is probably the slab

  2. A neurocomputational model of automatic sequence production.

    PubMed

    Helie, Sebastien; Roeder, Jessica L; Vucovich, Lauren; Rünger, Dennis; Ashby, F Gregory

    2015-07-01

    Most behaviors unfold in time and include a sequence of submovements or cognitive activities. In addition, most behaviors are automatic and repeated daily throughout life. Yet, relatively little is known about the neurobiology of automatic sequence production. Past research suggests a gradual transfer from the associative striatum to the sensorimotor striatum, but a number of more recent studies challenge this role of the BG in automatic sequence production. In this article, we propose a new neurocomputational model of automatic sequence production in which the main role of the BG is to train cortical-cortical connections within the premotor areas that are responsible for automatic sequence production. The new model is used to simulate four different data sets from human and nonhuman animals, including (1) behavioral data (e.g., RTs), (2) electrophysiology data (e.g., single-neuron recordings), (3) macrostructure data (e.g., TMS), and (4) neurological circuit data (e.g., inactivation studies). We conclude with a comparison of the new model with existing models of automatic sequence production and discuss a possible new role for the BG in automaticity and its implication for Parkinson's disease.

  3. Clustering metagenomic sequences with interpolated Markov models

    PubMed Central

    2010-01-01

    Background Sequencing of environmental DNA (often called metagenomics) has shown tremendous potential to uncover the vast number of unknown microbes that cannot be cultured and sequenced by traditional methods. Because the output from metagenomic sequencing is a large set of reads of unknown origin, clustering reads together that were sequenced from the same species is a crucial analysis step. Many effective approaches to this task rely on sequenced genomes in public databases, but these genomes are a highly biased sample that is not necessarily representative of environments interesting to many metagenomics projects. Results We present SCIMM (Sequence Clustering with Interpolated Markov Models), an unsupervised sequence clustering method. SCIMM achieves greater clustering accuracy than previous unsupervised approaches. We examine the limitations of unsupervised learning on complex datasets, and suggest a hybrid of SCIMM and supervised learning method Phymm called PHYSCIMM that performs better when evolutionarily close training genomes are available. Conclusions SCIMM and PHYSCIMM are highly accurate methods to cluster metagenomic sequences. SCIMM operates entirely unsupervised, making it ideal for environments containing mostly novel microbes. PHYSCIMM uses supervised learning to improve clustering in environments containing microbial strains from well-characterized genera. SCIMM and PHYSCIMM are available open source from http://www.cbcb.umd.edu/software/scimm. PMID:21044341

  4. Model of evolution of molecular sequences

    NASA Astrophysics Data System (ADS)

    Luo, Liaofu; Tsai, Lu; Lee, Weijiang

    1990-05-01

    A simplified model of the evolution of molecular sequences is proposed. An ensemble of strings is considered that consists of two letters and undergoes random point mutations and natural selections. A set of evolution equations is deduced. From the solution it is found that the first-order (second-order) informational parameters (redundancies) D1 decrease (D2 increase) in the course of evolution. Furthermore, the statistical correlations of the letters (bases) in the sequences are investigated in detail and the short-distance correlation is demonstrated. These results give a preliminary explanation of some physical aspects in the evolution of nucleic acid sequences.

  5. Aftershocks and on-site inspections under a test ban: A progress report

    SciTech Connect

    Smith, A.T.; Schultz, C.; Zucca, J.J.

    1995-09-01

    An ambiguous seismic event detected remotely under a comprehensive test ban (CTB) may require an on-site inspection to determine the nature of the event. Provided they are present, aftershocks and microseismic events could play a key role in narrowing the inspection area and focusing the efforts of the inspectors. Of particular interest are the low-frequency, emergent aftershocks that have been observed after underground nuclear explosions at the Nevada Test Site. If these events can be shown to have unique characteristics, their detection could greatly increase the chances for a successful inspection. The authors have been characterizing aftershock swarms from underground explosive events and from other events that may be encountered during an inspection. This report summarizes an analysis of aftershocks following an underground explosion and microseismic events associated with routine operations at the block-caving Henderson Mine in Colorado. They used as their example of a smaller, single-point explosion the Non-Proliferation Experiment (NPE), a one-kiloton, chemical, overburied, single-point explosion whose aftershock sequence is similar to an underground nuclear explosion. They were interested in studying the Henderson mine because the caving operation is an apparent analog to the chimney formation following an nuclear event and could give rise to similar microseismic events. Mine operations at Henderson result in both low-frequency emergent events and high-frequency impulsive events. The emergent events (hundreds per day) are apparently associated with rockfalls into the crater produced by the caving operations and have many similar characteristics to the low-frequency events from the NPE; however, the low-frequency NPE aftershocks are relatively much more impulsive than those of the Henderson Mine. Unlike the NPE or nuclear events, location of Henderson low-frequency events is extremely difficult using arrival-time methods because of their very gradual onset.

  6. The earthquake and its aftershocks from May 2 through September 30, 1983

    SciTech Connect

    Eaton, J.P.

    1990-01-01

    Analysis of the Coalinga earthquake sequence, based on the Allen/Ellis real-time-processor (RTP) automatic P-phase-onset times and duration measurements, provides hypocentral and magnitude determinations for more than 6,000 events from May 2 through September 30, 1983. Focal mechanisms and local magnitudes of more than 140 of the larger aftershocks were calculated from more detailed observations obtained from magnetic-tape playbacks from both the temporary Coalinga seismic network and the permanent telemetered central California seismic network (Calnet). The combined catalog appears to be substantially complete for events of M {ge} 3 within about 3 hours, and for events of M {ge} 1.7 within about 1 day, after the main shock. The first-motion plot of the main shock offers two choices for the main-shock fault; a thrust fault striking N. 53{degree}W. and dipping 23{degree}SW. (the preferred fault plane), or a high-angle reverse fault striking N. 53{degree}W. and dipping 67{degree}NE. Focal mechanisms of the larger aftershocks also indicate predominantly thrust or reverse faulting. The long axis of the aftershock zone, which is 35 km long and 15 to 20 km wide, coincides with the axis of the Anticline Ridge-Guijarral Hills structure at the Coast Ranges-Great Valley boundary northeast of Coalinga. A transverse (southwest to northeast) quiet band with very few events crosses the aftershock zone where northwest-trending Anticline Ridge joins broader, east-west-trending Joaquin Ridge just northwest of the main shock. The smaller aftershocks occur mostly in the hanging-wall blocks above the faults outlined by the larger aftershocks.

  7. An improved space-time ETAS model for inverting the rupture geometry from seismicity triggering

    NASA Astrophysics Data System (ADS)

    Guo, Yicun; Zhuang, Jiancang; Zhou, Shiyong

    2015-05-01

    This study incorporates the rupture geometry of big earthquakes in the formulation of the Epidemic-Type Aftershock Sequence (ETAS) model, which is a point process model widely applied in the study of spatiotemporal seismicity, rather than regarding every earthquake occurring at a point in space and time. We apply the new model to the catalog from Sichuan province, China, between 1990 and 2013, during which the Wenchuan Mw7.9 earthquake occurred in May 2008. Our results show that the modified model has better performance in both data fitting and aftershock simulation, confirming that the elliptic aftershock zone is caused by the superposition of the isotropic triggering effect from each patch of the rupture zone. Moreover, using the technique of stochastic reconstruction, we inverted the fault geometry and verified that direct aftershocks of the main shock more likely occur in the transitive parts from high-slip parts to low/median slip parts of the main shock fault area.

  8. Regional and stress drop effects on aftershock productivity of large megathrust earthquakes

    NASA Astrophysics Data System (ADS)

    Wetzler, Nadav; Brodsky, Emily E.; Lay, Thorne

    2016-12-01

    The total number of aftershocks increases with main shock magnitude, resulting in an overall well-defined relationship. Observed variations from this trend prompt questions regarding influences of regional environment and individual main shock rupture characteristics. We investigate how aftershock productivity varies regionally and with main shock source parameters for large (Mw ≥ 7.0) circum-Pacific megathrust earthquakes within the past 25 years, drawing on extant finite-fault rupture models. Aftershock productivity is found to be higher for subduction zones of the western circum-Pacific than for subduction zones in the eastern circum-Pacific. This appears to be a manifestation of differences in faulting susceptibility between island arcs and continental arcs. Surprisingly, events with relatively large static stress drop tend to produce fewer aftershocks than comparable magnitude events with lower stress drop; however, for events with similar coseismic rupture area, aftershock productivity increases with stress drop and radiated energy, indicating a significant impact of source rupture process on productivity.

  9. On the origin of diverse aftershock mechanisms following the 1989 Loma Prieta earthquake

    USGS Publications Warehouse

    Kilb, Debi; Ellis, M.; Gomberg, J.; Davis, S.

    1997-01-01

    We test the hypothesis that the origin of the diverse suite of aftershock mechanisms following the 1989 M 7.1 Loma Prieta, California, earthquake is related to the post-main-shock static stress field. We use a 3-D boundary-element algorithm to calculate static stresses, combined with a Coulomb failure criterion to calculate conjugate failure planes at aftershock locations. The post-main-shock static stress field is taken as the sum of a pre-existing stress field and changes in stress due to the heterogeneous slip across the Loma Prieta rupture plane. The background stress field is assumed to be either a simple shear parallel to the regional trend of the San Andreas fault or approximately fault-normal compression. A suite of synthetic aftershock mechanisms from the conjugate failure planes is generated and quantitatively compared (allowing for uncertainties in both mechanism parameters and earthquake locations) to well-constrained mechanisms reported in the US Geological Survey Northern California Seismic Network catalogue. We also compare calculated rakes with those observed by resolving the calculated stress tensor onto observed focal mechanism nodal planes, assuming either plane to be a likely rupture plane. Various permutations of the assumed background stress field, frictional coefficients of aftershock fault planes, methods of comparisons, etc. explain between 52 and 92 per cent of the aftershock mechanisms. We can explain a similar proportion of mechanisms however by comparing a randomly reordered catalogue with the various suites of synthetic aftershocks. The inability to duplicate aftershock mechanisms reliably on a one-to-one basis is probably a function of the combined uncertainties in models of main-shock slip distribution, the background stress field, and aftershock locations. In particular we show theoretically that any specific main-shock slip distribution and a reasonable background stress field are able to generate a highly variable suite of failure

  10. Determination of dip direction for the 2007 Chuetsu-oki earthquake from relocation of aftershocks using arrival times determined by cross-correlation

    NASA Astrophysics Data System (ADS)

    Mori, Jim

    2008-11-01

    Waveform correlations were used to redetermine P arrival times at 31 stations for a selected set of 321 aftershocks of the 2007 Chuetsu-oki earthquake. These data were used with several different relocation techniques, 1-D velocity structure, 3-D velocity structure using SIMULPS12, 1-D velocity structure using hypoDD, and 3-D velocity structure using tomoDD. The results from all of these methods show a consistent southeast dipping trend for the entire aftershock sequence. The same pattern is also seen for the time period before the largest aftershock. These results indicate that the mainshock fault dips to the southeast.

  11. Numerical testing of certain features of probabilistic aftershock hazard assessment

    NASA Astrophysics Data System (ADS)

    Gallovic, F.; Brokesova, J.

    2005-12-01

    Probabilistic aftershock hazard assessment (PAHA, Wiemer, 2000), provided for California in the frame of the STEP project, is based on a methodology having features, two of which are addressed in detail: 1) independence of parameter c in the Omori's law on a lower magnitude cut-off, and, 2) application attenuation relations in the expression for the probability of PGA exceedance. Concerning the first point, in STEP, c is assumed constant with respect to magnitude. However, in paper by Shcherbakov et al. (2004) the authors conclude that c scales with a lower magnitude cut-off. We show, using Japanese attenuation relations and four different earthquake models, that this modification change the hazard curves for very early time interval (<1 day) after the mainshock substantially. For later times (>1 day), the effect is minimal. As regards the second point, we try to substitute attenuation relations and their uncertainties by strong ground motion simulations for a set of scenarios. The main advantage of such an approach is that the simulations account for details of the aftershock source effects (faulting style, slip distribution, position of the nucleation point, etc.). Mean PGAs and their variances are retrieved from the simulations and they are used for the PAHA analysis at a station under study. The method is tested for the Izmit A25 aftershock (Mw=5.8) that occurred 26 days after the main shock. The resulting PAHA maps are compared with those obtained by the use of attenuation relations. We conclude that the two types of the PAHA maps do not differ significantly provided equal occurrence probability is assigned to each nucleation point location. However, possible constraint on this location (e.g., occurrence within the red Coulomb stress change areas) would change the maps considerably.

  12. Seismogenesis and earthquake triggering during the 2010-2011 Rigan (Iran) earthquake sequence

    NASA Astrophysics Data System (ADS)

    Mohammadi, Hiwa; Bayliss, Thomas J.; Nekouei Ghachkanlu, Esmaeil

    2017-02-01

    This study assesses the aftershock activity of two earthquakes that occurred on December 20, 2010 with magnitude of MN 6.5 (Global CMT Mw 6.5) and January 27, 2011 with magnitude of MN 6.0 (Global CMT Mw 6.2) in the Rigan region of southeastern Iran. This study has been done by assessing the statistical properties of the aftershock sequences associated with each of these earthquakes, namely b-value of Gutenberg-Richter relation, partitioning of radiated seismic energy, p-value of modified Omori law and the DC -value associated with the fractal dimension. The b-values of b = 0.89 ± 0.08 and b = 0.88 ± 0.08 were calculated for first main shock and second main shock sequence respectively. This suggests that this region is characterized by large differential stress; the genesis of large aftershock activity in a short time interval gives power this. Further, 2.2% of the whole energy is related with the aftershocks activity for first main shock sequence while 97.8% is associated with main shock; for second sequence, 20% of the total energy is associated with the aftershocks activity while 80% is associated with main shock. The p-values of 1.1 ± 0.12 and 1.1 ± 0.1 were calculated for first and second main shocks sequence respectively, which imply fast decay rate of aftershocks and high surface heat flux. A value of the spatial fractal dimension (Dc) equal to 2.34 ± 0.03 and 2.54 ± 0.02 for first and second main shocks sequence respectively, which reveals random spatial distribution and source in a two-dimensional plane that is being filled-up by fractures. Moreover, we then use the models to calculate the Coulomb stress change to appraise coming seismic hazard by inspecting the static Coulomb stress field due to these two main shocks for the recognition of the conceivable regions of aftershocks activity. The first main shock increased stress by more than 0.866 bars at the hypocenter of the second main shock, thus promoting the failure. In addition, the cumulative

  13. Seismotectonics and seismogenesis of Mw7.8 Gorkha earthquake and its aftershocks

    NASA Astrophysics Data System (ADS)

    Arora, B. R.; Bansal, B. K.; Prajapati, Sanjay K.; Sutar, Anup K.; Nayak, Shailesh

    2017-01-01

    The April 25, 2015, Mw7.8 Gorkha earthquake in central Nepal was followed by intense aftershock activity, including Mw6.7 shock on April 26, 2015 and Mw7.3 shock on May 12, 2015. Synthesis of the focal mechanisms, space-time distribution of seismic activity in relation to previously imaged crustal velocity and resistivity structures reveals focusing of the Mw7.8 Gorkha earthquake near the upper surface of the thin fluid-filled low velocity and high conducting layer immediately above the plane of the detachment. On the geophysical sections, the detachment is identified as a sharp positive velocity interface. Modulation of frictional coupling and mechanical weakening by high-pore pressure fluids counteract the arc-normal stresses creating conditions for failure and nucleation of the Gorkha earthquakes on a plane sub-parallel with the detachment. Spatio-temporal patterns in aftershock activity indicate rapid alteration of main shock-induced stress fields, triggering a strong aftershock of Mw6.7. Large stress drop and increased energy released by the Mw6.7 event facilitates upward injection of high pore-pressure fluid fluxes into the hidden out-of-sequence thrust. It is suggested that decrease in shear strength along the hidden thrust plane due to the diffusion of high pore pressure fluids created conditions favourable to trigger Mw7.3 aftershock.

  14. Towards Practical, Real-Time Estimation of Spatial Aftershock Probabilities: A Feasibility Study in Earthquake Hazard

    NASA Astrophysics Data System (ADS)

    Morrow, P.; McCloskey, J.; Steacy, S.

    2001-12-01

    extent to which this is scientifically feasible in terms of our understanding of the physical phenomena which control the variation of seismicity following a large event due to stress redistribution and practically possible given present limitations on data availability, data quality and computational or data transfer speeds. The project is divided into a number of elements designed to reflect the temporal sequence of tasks that must be undertaken for the prediction of aftershock hazard. These tasks include determining a time-indexed sequence of slip distributions for both real and synthetic events, calculating a suite of time-indexed stress perturbations and quantitatively comparing predicted and observed aftershock distributions, and developing techniques for predicting likely strong ground motion from the predicted spatial distribution of aftershocks.

  15. Triggering of earthquake aftershocks by dynamic stresses

    USGS Publications Warehouse

    Kilb, Debi; Gomberg, J.; Bodin, P.

    2000-01-01

    It is thought that small 'static' stress changes due to permanent fault displacement can alter the likelihood of, or trigger, earthquakes on nearby faults. Many studies of triggering in the nearfield, particularly of aftershocks, rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault. Here we report a comparison of the aftershock pattern of the moment magnitude MW = 7.3 Landers earthquake, not only with static stress changes but also with transient, oscillatory stress changes transmitted as seismic waves (that is, 'dynamic' stresses). Dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone. These dynamically weakened faults may fail after the seismic waves have passed by, and might even cause earthquakes that would not otherwise have occurred. We find similar asymmetries in the aftershock and dynamic stress patterns, the latter being due to rupture propagation, whereas the static stress changes lack this asymmetry. Previous studies have shown that dynamic stresses can promote failure at remote distances, but here we show that they can also do so nearby.

  16. Do aftershock probabilities decay with time?

    USGS Publications Warehouse

    Michael, Andrew J.

    2012-01-01

    So, do aftershock probabilities decay with time? Consider a thought experiment in which we are at the time of the mainshock and ask how many aftershocks will occur a day, week, month, year, or even a century from now. First we must decide how large a window to use around each point in time. Let's assume that, as we go further into the future, we are asking a less precise question. Perhaps a day from now means 1 day 10% of a day, a week from now means 1 week 10% of a week, and so on. If we ignore c because it is a small fraction of a day (e.g., Reasenberg and Jones, 1989, hereafter RJ89), and set p = 1 because it is usually close to 1 (its value in the original Omori law), then the rate of earthquakes (K=t) decays at 1=t. If the length of the windows being considered increases proportionally to t, then the number of earthquakes at any time from now is the same because the rate decrease is canceled by the increase in the window duration. Under these conditions we should never think "It's a bit late for this to be an aftershock."

  17. Forecasting large aftershocks within one day after the main shock

    PubMed Central

    Omi, Takahiro; Ogata, Yosihiko; Hirata, Yoshito; Aihara, Kazuyuki

    2013-01-01

    Forecasting the aftershock probability has been performed by the authorities to mitigate hazards in the disaster area after a main shock. However, despite the fact that most of large aftershocks occur within a day from the main shock, the operational forecasting has been very difficult during this time-period due to incomplete recording of early aftershocks. Here we propose a real-time method for efficiently forecasting the occurrence rates of potential aftershocks using systematically incomplete observations that are available in a few hours after the main shocks. We demonstrate the method's utility by retrospective early forecasting of the aftershock activity of the 2011 Tohoku-Oki Earthquake of M9.0 in Japan. Furthermore, we compare the results by the real-time data with the compiled preliminary data to examine robustness of the present method for the aftershocks of a recent inland earthquake in Japan. PMID:23860594

  18. Static stress triggering explains the empirical aftershock distance decay

    NASA Astrophysics Data System (ADS)

    Hainzl, Sebastian; Moradpour, Javad; Davidsen, Jörn

    2014-12-01

    The shape of the spatial aftershock decay is sensitive to the triggering mechanism and thus particularly useful for discriminating between static and dynamic stress triggering. For California seismicity, it has been recently recognized that its form is more complicated than typically assumed consisting of three different regimes with transitions at the scale of the rupture length and the thickness of the crust. The intermediate distance range is characterized by a relative small decay exponent of 1.35 previously declared to relate to dynamic stress triggering. We perform comprehensive simulations of a simple clock-advance model, in which the number of aftershocks is just proportional to the Coulomb-stress change, to test whether the empirical result can be explained by static stress triggering. Similarly to the observations, the results show three scaling regimes. For simulations adapted to the depths and focal mechanisms observed in California, we find a remarkable agreement with the observation over the whole distance range for a fault distribution with fractal dimension of 1.8, which is shown to be in good agreement with an independent analysis of California seismicity.

  19. Mixture of a seismicity model based on the rate-and-state friction and ETAS model

    NASA Astrophysics Data System (ADS)

    Iwata, T.

    2015-12-01

    Currently the ETAS model [Ogata, 1988, JASA] is considered to be a standard model of seismicity. However, because the ETAS model is a purely statistical one, the physics-based seismicity model derived from the rate-and-state friction (hereafter referred to as Dieterich model) [Dieterich, 1994, JGR] is frequently examined. However, the original version of the Dieterich model has several problems in the application to real earthquake sequences and therefore modifications have been conducted in previous studies. Iwata [2015, Pageoph] is one of such studies and shows that the Dieterich model is significantly improved as a result of the inclusion of the effect of secondary aftershocks (i.e., aftershocks caused by previous aftershocks). However, still the performance of the ETAS model is superior to that of the improved Dieterich model. For further improvement, the mixture of the Dieterich and ETAS models is examined in this study. To achieve the mixture, the seismicity rate is represented as a sum of the ETAS and Dieterich models of which weights are given as k and 1-k, respectively. This mixture model is applied to the aftershock sequences of the 1995 Kobe and 2004 Mid-Niigata sequences which have been analyzed in Iwata [2015]. Additionally, the sequence of the Matsushiro earthquake swarm in central Japan 1965-1970 is also analyzed. The value of k and parameters of the ETAS and Dieterich models are estimated by means of the maximum likelihood method, and the model performances are assessed on the basis of AIC. For the two aftershock sequences, the AIC values of the ETAS model are around 3-9 smaller (i.e., better) than those of the mixture model. On the contrary, for the Matsushiro swarm, the AIC value of the mixture model is 5.8 smaller than that of the ETAS model, indicating that the mixture of the two models results in significant improvement of the seismicity model.

  20. Fetal akinesia deformation sequence: an animal model.

    PubMed

    Moessinger, A C

    1983-12-01

    Rat fetuses were paralyzed by daily transuterine injections of curare from day 18 of gestation until term (day 21). The following anomalies were noted at the time of delivery: multiple joint contractures, pulmonary hypoplasia, micrognathia, fetal growth retardation, short umbilical cords, and polyhydramnios. Neither sham-operated nor untouched littermate control fetuses had any of these anomalies. The group of anomalies (or deformation sequence) obtained with this animal model is presumed to result from the paralytic effect of curare. This phenotype bears a striking resemblance to the syndrome of ankyloses, facial anomalies, and pulmonary hypoplasia (also known as Pena and Shokeir I), presumably inherited in an autosomal recessive manner. It is suggested that this phenotype is not specific but, rather, represents a deformation sequence which results from fetal immobilization or akinesia. Diagnostic evaluation of patients with this group of anomalies should include the identification of the underlying pathologic process (etiology of the akinesia) to allow for proper classification and genetic counseling.

  1. Increasing lengths of aftershock zones with depths of moderate-size earthquakes on the San Jacinto Fault suggests triggering of deep creep in the middle crust

    NASA Astrophysics Data System (ADS)

    Meng, Xiaofeng; Peng, Zhigang

    2016-01-01

    Recent geodetic studies along the San Jacinto Fault (SJF) in southern California revealed a shallower locking depth than the seismogenic depth outlined by microseismicity. This disagreement leads to speculations that creeping episodes drive seismicity in the lower part of the seismogenic zone. Whether deep creep occurs along the SJF holds key information on how fault slips during earthquake cycle and potential seismic hazard imposed to southern California. Here we apply a matched filter technique to 10 M > 4 earthquake sequences along the SJF since 2000 and obtain more complete earthquake catalogues. We then systematic investigate spatio-temporal evolutions of these aftershock sequences. We find anomalously large aftershock zones for earthquakes occurred below the geodetically inferred locking depth (i.e. 11-12 km), while aftershock zones of shallower main shocks are close to expectations from standard scaling relationships. Although we do not observe clear migration of aftershocks, most aftershock zones do expand systematically with logarithmic time since the main shock. All the evidences suggest that aftershocks near or below the locking depth are likely driven by deep creep following the main shock. The presence of a creeping zone below 11-12 km may have significant implications on the maximum sizes of events in this region.

  2. Power-law Distributions of Offspring and Generation Numbers in Branching Models of Earthquake Triggering

    NASA Astrophysics Data System (ADS)

    Saichev, A.; Helmstetter, A.; Sornette, D.

    2005-06-01

    We consider a general stochastic branching process,which is relevant to earthquakes as well as to many other systems, and we study the distributions of the total number of offsprings (direct and indirect aftershocks in seismicity) and of the total number of generations before extinction. We apply our results to a branching model of triggered seismicity, the ETAS (epidemic-type aftershock sequence) model. The ETAS model assumes that each earthquake can trigger other earthquakes (“aftershocks”). An aftershock sequence results in this model from the cascade of aftershocks of each past earthquake. Due to the large fluctuations of the number of aftershocks triggered directly by any earthquake (“fertility”), there is a large variability of the total number of aftershocks from one sequence to another, for the same mainshock magnitude. We study the regime in which the distribution of fertilities μ is characterized by a power law ~1/μ1+γ. For earthquakes we expect such a power-distribution of fertilities with γ=b/α based on the Gutenberg-Richter magnitude distribution ~ 10-bm and on the increase ~ 10-αm of the number of aftershocks with the mainshock magnitude m. We derive the asymptotic distributions pr(r) and pg(g) of the total number r of offsprings and of the total number g of generations until extinction following a mainshock. In the regime γ < 2 for which the distribution of fertilities has an infinite variance, we find This should be compared with the distributions obtained for standard branching processes with finite variance. These predictions are checked by numerical simulations. Our results apply directly to the ETAS model whose preferred values α=0.8 1 and b=1 puts it in the regime where the distribution of fertilities has an infinite variance. More generally, our results apply to any stochastic branching process with a power-law distribution of offsprings per mother

  3. Local near instantaneously dynamically triggered aftershocks of large earthquakes.

    PubMed

    Fan, Wenyuan; Shearer, Peter M

    2016-09-09

    Aftershocks are often triggered by static- and/or dynamic-stress changes caused by mainshocks. The relative importance of the two triggering mechanisms is controversial at near-to-intermediate distances. We detected and located 48 previously unidentified large early aftershocks triggered by earthquakes with magnitudes between ≥7 and 8 within a few fault lengths (approximately 300 kilometers), during times that high-amplitude surface waves arrive from the mainshock (less than 200 seconds). The observations indicate that near-to-intermediate-field dynamic triggering commonly exists and fundamentally promotes aftershock occurrence. The mainshocks and their nearby early aftershocks are located at major subduction zones and continental boundaries, and mainshocks with all types of faulting-mechanisms (normal, reverse, and strike-slip) can trigger early aftershocks.

  4. Joint inversion of teleseismic body-waves and geodetic data for the Mw6.8 aftershock of the Balochistan earthquake with refined epicenter location

    NASA Astrophysics Data System (ADS)

    Wei, S.; Wang, T.; Jonsson, S.; Avouac, J. P.; Helmberger, D. V.

    2014-12-01

    Aftershocks of the 2013 Balochistan earthquake are mainly concentrated along the northeastern end of the mainshock rupture despite of much larger coseismic slip to the southwest. The largest event among them is an Mw6.8 earthquake which occurred three days after the mainshock. A kinematic slip model of the mainshock was obtained by joint inversion of the teleseismic body-waves and horizontal static deformation field derived from remote sensing optical and SAR data, which is composed of seven fault segments with gradually changing strikes and dips [Avouac et al., 2014]. The remote sensing data provide well constraints on the fault geometry and spatial distribution of slip but no timing information. Meanwhile, the initiation of the teleseismic waveform is very sensitive to fault geometry of the epicenter segment (strike and dip) and spatial slip distribution but much less sensitive to the absolute location of the epicenter. The combination of the two data sets allows a much better determination of the absolute epicenter location, which is about 25km to the southwest of the NEIC epicenter location. The well located mainshock epicenter is used to establish path calibrations for teleseismic P-waves, which are essential for relocating the Mw6.8 aftershock. Our grid search shows that the refined epicenter is located right at the northeastern end of the mainshock rupture. This is confirmed by the SAR offsets calculated from images acquired after the mainshock. The azimuth and range offsets display a discontinuity across the rupture trace of the mainshock. Teleseismic only and static only, as well as joint inversions all indicate that the aftershock ruptured an asperity with 25km along strike and range from 8km to 20km in depth. The earthquake was originated in a positive Coulomb stress change regime due to the mainshock and has complementary slip distribution to the mainshock rupture at the northeastern end, suggesting that the entire seismic generic zone in the crust was

  5. Near real-time aftershock hazard maps for earthquakes

    NASA Astrophysics Data System (ADS)

    McCloskey, J.; Nalbant, S. S.

    2009-04-01

    Stress interaction modelling is routinely used to explain the spatial relationships between earthquakes and their aftershocks. On 28 October 2008 a M6.4 earthquake occurred near the Pakistan-Afghanistan border killing several hundred and causing widespread devastation. A second M6.4 event occurred 12 hours later 20km to the south east. By making some well supported assumptions concerning the source event and the geometry of any likely triggered event it was possible to map those areas most likely to experience further activity. Using Google earth, it would further have been possible to identify particular settlements in the source area which were particularly at risk and to publish their locations globally within about 3 hours of the first earthquake. Such actions could have significantly focused the initial emergency response management. We argue for routine prospective testing of such forecasts and dialogue between social and physical scientists and emergency response professionals around the practical application of these techniques.

  6. Aftershocks of the India Republic Day Earthquake: the MAEC/ISTAR Temporary Seismograph Network

    NASA Astrophysics Data System (ADS)

    Bodin, P.; Horton, S.; Johnston, A.; Patterson, G.; Bollwerk, J.; Rydelek, P.; Steiner, G.; McGoldrick, C.; Budhbhatti, K. P.; Shah, R.; Macwan, N.

    2001-05-01

    The MW=7.7 Republic Day (26 January, 2001) earthquake on the Kachchh in western India initiated a strong sequence of small aftershocks. Seventeen days following the mainshock, we deployed a network of portable digital event recorders as a cooperative project of the Mid America Earthquake Center in the US and the Institute for Scientific and Technological Advanced Research. Our network consisted of 8 event-triggered Kinemetrics K2 seismographs with 6 data channels (3 accelerometer, 3 Mark L-28/3d seismometer) sampled at 200 Hz, and one continuously-recording Guralp CMG40TD broad-band seismometer sampled at 220 Hz. This network was in place for 18 days. Underlying our network deployment was the notion that because of its tectonic and geologic setting the Republic Day earthquake and its aftershocks might have source and/or propagation characteristics common to earthquakes in stable continental plate-interiors rather than those on plate boundaries or within continental mobile belts. Thus, our goals were to provide data that could be used to compare the Republic Day earthquake with other earthquakes. In particular, the objectives of our network deployment were: (1) to characterize the spatial distribution and occurrence rates of aftershocks, (2) to examine source characteristics of the aftershocks (stress-drops, focal mechanisms), (3) to study the effect of deep unconsolidated sediment on wave propagation, and (4) to determine if other faults (notably the Allah Bundh) were simultaneously active. Most of our sites were on Jurassic bedrock, and all were either free-field, or on the floor of light structures built on rock or with a thin soil cover. However, one of our stations was on a section of unconsolidated sediments hundreds of meters thick adjacent to a site that was subjected to shaking-induced sediment liquefaction during the mainshock. The largest aftershock reported by global networks was an MW=5.9 event on January 28, prior to our deployment. The largest

  7. 3D imaging of crustal structure under the Piedmont province in central Virginia, from reflection RVSP processing of aftershock recordings from the August 23, 2011 Virginia earthquake

    NASA Astrophysics Data System (ADS)

    Quiros, D. A.; Brown, L. D.; Cabolova, A.; Davenport, K. K.; Hole, J. A.; Mooney, W. D.

    2013-12-01

    Aftershocks from the magnitude Mw 5.8 August 23, 2011, central Virginia earthquake were recorded using an unusually dense array of seismometers in what has been termed an AIDA (Aftershock Imaging with Dense Arrays) deployment. Over 200 stations were deployed in the epicentral region of this event to a) more precisely determine hypocentral locations, b) more accurately define velocity structure in the aftershock zone, c) characterize propagation characteristics of the crust in the area, and d) image geologic structures in the hypocentral volume with reflection techniques using aftershocks as sources. The AIDA-Virginia experiment successfully recorded a large number of aftershocks from which local tomographic velocity estimates and accurate hypocentral locations were obtained. These results facilitated the use of aftershocks as sources for reflection imaging. In this study we demonstrate how earthquake sources recorded by surface arrays can be treated using the imaging techniques associated with Vertical Seismic Profiling (VSP), in particular a variant known as Reverse VSP (RVSP). The central VSP processing algorithms used for this study are VSP normal moveout (VSPnmo) and VSP-to-Common Reflection Point (CRP). Applying these techniques to individual aftershocks from the Virginia experiment results in 3D reflection images of structural complexity in the immediate vicinity of the aftershocks. The most prominent feature observed on these 3D images is a strong moderately east-dipping reflector at a depth of approximately 6 to 8 km that directly underlies, and is continuous beneath, the more steeply dipping aftershock zone. We interpret this reflector as part of a complex imbricate thrust sequence associated with Paleozoic convergence during the Appalachian orogeny. Its apparent continuity beneath the fault zone implied by the aftershock's hypocenters suggests that this inferred fault zone has little or no cumulative offset, supporting the speculation that this event

  8. Teleseismic depth estimation of the 2015 Gorkha-Nepal aftershocks

    NASA Astrophysics Data System (ADS)

    Letort, Jean; Bollinger, Laurent; Lyon-Caen, Helene; Guilhem, Aurélie; Cano, Yoann; Baillard, Christian; Adhikari, Lok Bijaya

    2016-12-01

    The depth of 61 aftershocks of the 2015 April 25 Gorkha, Nepal earthquake, that occurred within the first 20 d following the main shock, is constrained using time delays between teleseismic P phases and depth phases (pP and sP). The detection and identification of these phases are automatically processed using the cepstral method developed by Letort et al., and are validated with computed radiation patterns from the most probable focal mechanisms. The events are found to be relatively shallow (13.1 ± 3.9 km). Because depth estimations could potentially be biased by the method, velocity model or selected data, we also evaluate the depth resolution of the events from local catalogues by extracting 138 events with assumed well-constrained depth estimations. Comparison between the teleseismic depths and the depths from local and regional catalogues helps decrease epistemic uncertainties, and shows that the seismicity is clustered in a narrow band between 10 and 15 km depth. Given the geometry and depth of the major tectonic structures, most aftershocks are probably located in the immediate vicinity of the Main Himalayan Thrust (MHT) shear zone. The mid-crustal ramp of the flat/ramp MHT system is not resolved indicating that its height is moderate (less than 5-10 km) in the trace of the sections that ruptured on April 25. However, the seismicity depth range widens and deepens through an adjacent section to the east, a region that failed on 2015 May 12 during an Mw 7.3 earthquake. This deeper seismicity could reflect a step-down of the basal detachment of the MHT, a lateral structural variation which probably acted as a barrier to the dynamic rupture propagation.

  9. Stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 Northridge, California, earthquake

    USGS Publications Warehouse

    Deng, J.; Hudnut, K.; Gurnis, M.; Hauksson, E.

    1999-01-01

    Following the M(w) 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.Following the Mw 6.7 Northridge earthquake, significant postseismic displacements were resolved with GPS. Using a three-dimensional viscoelastic model, we suggest that this deformation is mainly driven by viscous flow in the lower crust. Such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate. Most aftershocks within the rupture zone, especially those that occurred after the first several weeks of the main shock, may have been triggered by continuous stress loading from viscous flow. The long-term decay time of aftershocks (about 2 years) approximately matches the decay of viscoelastic loading, and thus is controlled by the viscosity of the lower crust. Our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow.

  10. Delineating complex spatiotemporal distribution of earthquake aftershocks: an improved Source-Scanning Algorithm

    NASA Astrophysics Data System (ADS)

    Liao, Yen-Che; Kao, Honn; Rosenberger, Andreas; Hsu, Shu-Kun; Huang, Bor-Shouh

    2012-06-01

    Conventional earthquake location methods depend critically on the correct identification of seismic phases and their arrival times from seismograms. Accurate phase picking is particularly difficult for aftershocks that occur closely in time and space, mostly because of the ambiguity of correlating the same phase at different stations. In this study, we introduce an improved Source-Scanning Algorithm (ISSA) for the purpose of delineating the complex distribution of aftershocks without time-consuming and labour-intensive phase-picking procedures. The improvements include the application of a ground motion analyser to separate P and S waves, the automatic adjustment of time windows for 'brightness' calculation based on the scanning resolution and a modified brightness function to combine constraints from multiple phases. Synthetic experiments simulating a challenging scenario are conducted to demonstrate the robustness of the ISSA. The method is applied to a field data set selected from the ocean-bottom-seismograph records of an offshore aftershock sequence southwest of Taiwan. Although visual inspection of the seismograms is ambiguous, our ISSA analysis clearly delineates two events that can best explain the observed waveform pattern.

  11. Simultaneous estimation of b-values and detection rates of earthquakes for the application to aftershock probability forecasting

    NASA Astrophysics Data System (ADS)

    Katsura, K.; Ogata, Y.

    2004-12-01

    Reasenberg and Jones [Science, 1989, 1994] proposed the aftershock probability forecasting based on the joint distribution [Utsu, J. Fac. Sci. Hokkaido Univ., 1970] of the modified Omori formula of aftershock decay and Gutenberg-Richter law of magnitude frequency, where the respective parameters are estimated by the maximum likelihood method [Ogata, J. Phys. Earth, 1983; Utsu, Geophys Bull. Hokkaido Univ., 1965, Aki, Bull. Earthq. Res. Inst., 1965]. The public forecast has been implemented by the responsible agencies in California and Japan. However, a considerable difficulty in the above procedure is that, due to the contamination of arriving seismic waves, detection rate of aftershocks is extremely low during a period immediately after the main shock, say, during the first day, when the forecasting is most critical for public in the affected area. Therefore, for the forecasting of a probability during such a period, they adopt a generic model with a set of the standard parameter values in California or Japan. For an effective and realistic estimation, I propose to utilize the statistical model introduced by Ogata and Katsura [Geophys. J. Int., 1993] for the simultaneous estimation of the b-values of Gutenberg-Richter law together with detection-rate (probability) of earthquakes of each magnitude-band from the provided data of all detected events, where the both parameters are allowed for changing in time. Thus, by using all detected aftershocks from the beginning of the period, we can estimate the underlying modified Omori rate of both detected and undetected events and their b-value changes, taking the time-varying missing rates of events into account. The similar computation is applied to the ETAS model for complex aftershock activity or regional seismicity where substantial missing events are expected immediately after a large aftershock or another strong earthquake in the vicinity. Demonstrations of the present procedure will be shown for the recent examples

  12. Mixture of experts models to exploit global sequence similarity on biomolecular sequence labeling

    PubMed Central

    Caragea, Cornelia; Sinapov, Jivko; Dobbs, Drena; Honavar, Vasant

    2009-01-01

    Background Identification of functionally important sites in biomolecular sequences has broad applications ranging from rational drug design to the analysis of metabolic and signal transduction networks. Experimental determination of such sites lags far behind the number of known biomolecular sequences. Hence, there is a need to develop reliable computational methods for identifying functionally important sites from biomolecular sequences. Results We present a mixture of experts approach to biomolecular sequence labeling that takes into account the global similarity between biomolecular sequences. Our approach combines unsupervised and supervised learning techniques. Given a set of sequences and a similarity measure defined on pairs of sequences, we learn a mixture of experts model by using spectral clustering to learn the hierarchical structure of the model and by using bayesian techniques to combine the predictions of the experts. We evaluate our approach on two biomolecular sequence labeling problems: RNA-protein and DNA-protein interface prediction problems. The results of our experiments show that global sequence similarity can be exploited to improve the performance of classifiers trained to label biomolecular sequence data. Conclusion The mixture of experts model helps improve the performance of machine learning methods for identifying functionally important sites in biomolecular sequences. PMID:19426452

  13. Seismic moment tensor inversion using 3D velocity model and its application to the 2013 Lushan earthquake sequence

    NASA Astrophysics Data System (ADS)

    Zhu, Lupei; Zhou, Xiaofeng

    2016-10-01

    Source inversion of small-magnitude events such as aftershocks or mine collapses requires use of relatively high frequency seismic waveforms which are strongly affected by small-scale heterogeneities in the crust. In this study, we developed a new inversion method called gCAP3D for determining general moment tensor of a seismic source using Green's functions of 3D models. It inherits the advantageous features of the "Cut-and-Paste" (CAP) method to break a full seismogram into the Pnl and surface-wave segments and to allow time shift between observed and predicted waveforms. It uses grid search for 5 source parameters (relative strengths of the isotropic and compensated-linear-vector-dipole components and the strike, dip, and rake of the double-couple component) that minimize the waveform misfit. The scalar moment is estimated using the ratio of L2 norms of the data and synthetics. Focal depth can also be determined by repeating the inversion at different depths. We applied gCAP3D to the 2013 Ms 7.0 Lushan earthquake and its aftershocks using a 3D crustal-upper mantle velocity model derived from ambient noise tomography in the region. We first relocated the events using the double-difference method. We then used the finite-differences method and reciprocity principle to calculate Green's functions of the 3D model for 20 permanent broadband seismic stations within 200 km from the source region. We obtained moment tensors of the mainshock and 74 aftershocks ranging from Mw 5.2 to 3.4. The results show that the Lushan earthquake is a reverse faulting at a depth of 13-15 km on a plane dipping 40-47° to N46° W. Most of the aftershocks occurred off the main rupture plane and have similar focal mechanisms to the mainshock's, except in the proximity of the mainshock where the aftershocks' focal mechanisms display some variations.

  14. Distribution of similar earthquakes in aftershocks of inland earthquakes

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Hiramatsu, Y.; Aftershock Observations Of 2007 Noto Hanto, G.

    2010-12-01

    Frictional properties control the slip behavior on a fault surface such as seismic slip and aseismic slip. Asperity, as a seismic slip area, is characterized by a strong coupling in the interseismic period and large coseismic slip. On the other hand, steady slip or afterslip occurs in an aseismic slip area around the asperity. If an afterslip area includes small asperities, a repeating rupture of single asperity can generate similar earthquakes due to the stress accumulation caused by the afterslip. We here investigate a detail distribution of similar earthquakes in the aftershocks of the 2007 Noto Hanto earthquake (Mjma 6.9) and the 2000 Western Tottori earthquake (Mjma 7.3), inland large earthquakes in Japan. We use the data obtained by the group for the aftershock observations of the 2007 Noto Hanto Earthquake and by the group for the aftershock observations of the 2000 Western Tottori earthquake. First, we select pairs of aftershocks whose cross correlation coefficients in 10 s time window of band-pass filtered waveforms of 1~4 Hz are greater than 0.95 at more than 5 stations and divide those into groups by a link of the cross correlation coefficients. Second, we reexamine the arrival times of P and S waves and the maximum amplitude for earthquakes of each group and apply the double-difference method (Waldhouser and Ellsworth, 2000) to relocate them. As a result of the analysis, we find 24 groups of similar earthquakes in the aftershocks on the source fault of the 2007 Noto Hanto Earthquake and 86 groups of similar earthquakes in the aftershocks on the source fault of the 2000 Western Tottori Earthquake. Most of them are distributed around or outside the asperity of the main shock. Geodetic studies reported that postseismic deformation was detected for the both earthquakes (Sagiya et al., 2002; Hashimoto et al., 2008). The source area of similar earthquakes seems to correspond to the afterslip area. These features suggest that the similar earthquakes observed

  15. Aftershocks of the western Argentina (Caucete) earthquake of 23 November 1977: some tectonic implications

    USGS Publications Warehouse

    Langer, C.J.; Bollinger, G.A.

    1988-01-01

    An aftershock survey, using a network of eight portable and two permanent seismographs, was conducted for the western Argentina (Caucete) earthquake (MS 7.3) of November 23, 1977. Monitoring began December 6, almost 2 weeks after the main shock and continued for 11 days. The data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km. The spatial distribution of those events occupied a volume of about 100 km long ??50 km wide ??30 km thick. The volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east- and west-dipping planar zones. Efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region. Our focal depth (25-35 km) and modeling studies lead us to prefer an east-dipping plane as causal. A previous interpretation by other investigators used a shallower focal depth (17 km) and similar modeling calculations in choosing a west-dipping plane. Our selection of the east-dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer (rather than in the middle of that layer) which requires fault propagation to be updip (rather than downdip). ?? 1988.

  16. Gravity and magnetic anomalies used to delineate geologic features associated with earthquakes and aftershocks in the central Virginia seismic zone

    NASA Astrophysics Data System (ADS)

    Shah, A. K.; Horton, J.; McNamara, D. E.; Spears, D.; Burton, W. C.

    2013-12-01

    Estimating seismic hazard in intraplate environments can be challenging partly because events are relatively rare and associated data thus limited. Additionally, in areas such as the central Virginia seismic zone, numerous pre-existing faults may or may not be candidates for modern tectonic activity, and other faults may not have been mapped. It is thus important to determine whether or not specific geologic features are associated with seismic events. Geophysical and geologic data collected in response to the Mw5.8 August 23, 2011 central Virginia earthquake provide excellent tools for this purpose. Portable seismographs deployed within days of the main shock showed a series of aftershocks mostly occurring at depths of 3-8 km along a southeast-dipping tabular zone ~10 km long, interpreted as the causative fault or fault zone. These instruments also recorded shallow (< 4 km) aftershocks clustered in several areas at distances of ~2-15 km from the main fault zone. We use new airborne geophysical surveys (gravity, magnetics, radiometrics, and LiDAR) to delineate the distribution of various surface and subsurface geologic features of interest in areas where the earthquake and aftershocks took place. The main (causative fault) aftershock cluster coincides with a linear, NE-trending gravity gradient (~ 2 mgal/km) that extends over 20 km in either direction from the Mw5.8 epicenter. Gravity modeling incorporating seismic estimates of Moho variations suggests the presence of a shallow low-density body overlying the main aftershock cluster, placing it within the upper 2-4 km of the main-fault hanging wall. The gravity, magnetic, and radiometric data also show a bend in generally NE-SW orientation of anomalies close to the Mw5.8 epicenter. Most shallow aftershock clusters occur near weaker short-wavelength gravity gradients of one to several km length. In several cases these gradients correspond to geologic contacts mapped at the surface. Along the gravity gradients, the

  17. Comparison of Short-term and Long-term Earthquake Forecast Models for Southern California

    NASA Astrophysics Data System (ADS)

    Helmstetter, A.; Kagan, Y. Y.; Jackson, D. D.

    2004-12-01

    Many earthquakes are triggered in part by preceding events. Aftershocks are the most obvious examples, but many large earthquakes are preceded by smaller ones. The large fluctuations of seismicity rate due to earthquake interactions thus provide a way to improve earthquake forecasting significantly. We have developed a model to estimate daily earthquake probabilities in Southern California, using the Epidemic Type Earthquake Sequence model [Kagan and Knopoff, 1987; Ogata, 1988]. The forecasted seismicity rate is the sum of a constant external loading and of the aftershocks of all past earthquakes. The background rate is estimated by smoothing past seismicity. Each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and which decreases with time following Omori's law. We use an isotropic kernel to model the spatial distribution of aftershocks for small (M≤5.5) mainshocks, and a smoothing of the location of early aftershocks for larger mainshocks. The model also assumes that all earthquake magnitudes follow the Gutenberg-Richter law with a unifom b-value. We use a maximum likelihood method to estimate the model parameters and tests the short-term and long-term forecasts. A retrospective test using a daily update of the forecasts between 1985/1/1 and 2004/3/10 shows that the short-term model decreases the uncertainty of an earthquake occurrence by a factor of about 10.

  18. Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

  19. Teleseismic Body Wave Analysis for the 27 September 2003 Altai, Earthquake (Mw7.4) and Large Aftershocks

    NASA Astrophysics Data System (ADS)

    Gomez-Gonzalez, J. M.; Mellors, R.

    2007-05-01

    We investigate the kinematics of the rupture process for the September 27, 2003, Mw7.3, Altai earthquake and its associated large aftershocks. This is the largest earthquake striking the Altai mountains within the last 50 years, which provides important constraints on the ongoing tectonics. The fault plane solution obtained by teleseismic body waveform modeling indicated a predominantly strike-slip event (strike=130, dip=75, rake 170), Scalar moment for the main shock ranges from 0.688 to 1.196E+20 N m, a source duration of about 20 to 42 s, and an average centroid depth of 10 km. Source duration would indicate a fault length of about 130 - 270 km. The main shock was followed closely by two aftershocks (Mw5.7, Mw6.4) occurred the same day, another aftershock (Mw6.7) occurred on 1 October , 2003. We also modeled the second aftershock (Mw6.4) to asses geometric similarities during their respective rupture process. This aftershock occurred spatially very close to the mainshock and possesses a similar fault plane solution (strike=128, dip=71, rake=154), and centroid depth (13 km). Several local conditions, such as the crustal model and fault geometry, affect the correct estimation of some source parameters. We perfume a sensitivity evaluation of several parameters, including centroid depth, scalar moment and source duration, based on a point and finite source modeling. The point source approximation results are the departure parameters for the finite source exploration. We evaluate the different reported parameters to discard poor constrained models. In addition, deformation data acquired by InSAR are also included in the analysis.

  20. Diversity of the 2014 Iquique's foreshocks and aftershocks: clues about the complex rupture process of a Mw 8.1 earthquake

    NASA Astrophysics Data System (ADS)

    León-Ríos, Sergio; Ruiz, Sergio; Maksymowicz, Andrei; Leyton, Felipe; Fuenzalida, Amaya; Madariaga, Raúl

    2016-10-01

    We study the foreshocks and aftershocks of the 1 April 2014 Iquique earthquake of Mw 8.1. Most of these events were recorded by a large digital seismic network that included the Northern Chile permanent network and up to 26 temporary broadband digital stations. We relocated and computed moment tensors for 151 events of magnitude Mw ≥ 4.5. Most of the foreshocks and aftershocks of the Iquique earthquake are distributed to the southwest of the rupture zone. These events are located in a band of about 50 km from the trench, an area where few earthquakes occur elsewhere in Chile. Another important group of aftershocks is located above the plate interface, similar to those observed during the foreshock sequence. The depths of these events were constrained by regional moment tensor (RMT) solutions obtained using the records of the dense broad band network. The majority of the foreshocks and aftershocks were associated to the interplate contact, with dip and strike angles in good agreement with the characteristics of horst and graben structures (>2000 m offset) typical of the oceanic Nazca Plate at the trench and in the outer rise region. We propose that the spatial distribution of foreshocks and aftershocks, and its seismological characteristics were strongly controlled by the rheological and tectonics conditions of the extreme erosive margin of Northern Chile.

  1. An improved space-time ETAS model for inverting the rupture geometry from seismicity triggering

    NASA Astrophysics Data System (ADS)

    Guo, Y.; Zhuang, J.; Zhou, S.; Gao, Y.

    2015-12-01

    This study incorporates the rupture geometry of big earthquakes in the formulation of theEpidemic-Type Aftershock Sequence (ETAS) model, which is a point process model widely applied in thestudy of spatiotemporal seismicity, rather than regarding every earthquake occurring at a point in space andtime. We apply the new model to the catalog from Sichuan province, China, between 1990 and 2013, duringwhich the Wenchuan Mw7.9 earthquake occurred in May 2008. Our results show that the modified modelhas better performance in both data fitting and aftershock simulation, confirming that the elliptic aftershockzone is caused by the superposition of the isotropic triggering effect from each patch of the rupture zone.Moreover, using the technique of stochastic reconstruction, we inverted the fault geometry and verifiedthat direct aftershocks of the main shock more likely occur in the transitive parts from high-slip parts tolow/median slip parts of the main shock fault area.

  2. Probabilistic models for semisupervised discriminative motif discovery in DNA sequences.

    PubMed

    Kim, Jong Kyoung; Choi, Seungjin

    2011-01-01

    Methods for discriminative motif discovery in DNA sequences identify transcription factor binding sites (TFBSs), searching only for patterns that differentiate two sets (positive and negative sets) of sequences. On one hand, discriminative methods increase the sensitivity and specificity of motif discovery, compared to generative models. On the other hand, generative models can easily exploit unlabeled sequences to better detect functional motifs when labeled training samples are limited. In this paper, we develop a hybrid generative/discriminative model which enables us to make use of unlabeled sequences in the framework of discriminative motif discovery, leading to semisupervised discriminative motif discovery. Numerical experiments on yeast ChIP-chip data for discovering DNA motifs demonstrate that the best performance is obtained between the purely-generative and the purely-discriminative and the semisupervised learning improves the performance when labeled sequences are limited.

  3. Analysis of rupture area of aftershocks caused by twin earthquakes (Case study: 11 April 2012 earthquakes of Aceh-North Sumatra)

    SciTech Connect

    Diansari, Angga Vertika Purwana, Ibnu; Subakti, Hendri

    2015-04-24

    The 11 April 2012 earthquakes off-shore Aceh-North Sumatra are unique events for the history of Indonesian earthquake. It is unique because that they have similar magnitude, 8.5 Mw and 8.1 Mw; close to epicenter distance, similar strike-slip focal mechanism, and occuring in outer rise area. The purposes of this research are: (1) comparing area of earthquakes base on models and that of calculation, (2) fitting the shape and the area of earthquake rupture zones, (3) analyzing the relationship between rupture area and magnitude of the earthquakes. Rupture area of the earthquake fault are determined by using 4 different formulas, i.e. Utsu and Seki (1954), Wells and Coppersmith (1994), Ellsworth (2003), and Christophersen and Smith (2000). The earthquakes aftershock parameters are taken from PGN (PusatGempabumiNasional or National Earthquake Information Center) of BMKG (Indonesia Agency Meteorology Climatology and Geophysics). The aftershock epicenters are plotted by GMT’s software. After that, ellipse and rectangular models of aftershock spreading are made. The results show that: (1) rupture areas were calculated using magnitude relationship which are larger than the the aftershock distributions model, (2) the best fitting model for that earthquake aftershock distribution is rectangular associated with Utsu and Seki (1954) formula, (3) the larger the magnitude of the earthquake, the larger area of the fault.

  4. Aftershock activity of the 2015 Gorkha, Nepal, earthquake determined using the Kathmandu strong motion seismographic array

    NASA Astrophysics Data System (ADS)

    Ichiyanagi, Masayoshi; Takai, Nobuo; Shigefuji, Michiko; Bijukchhen, Subeg; Sasatani, Tsutomu; Rajaure, Sudhir; Dhital, Megh Raj; Takahashi, Hiroaki

    2016-02-01

    The characteristics of aftershock activity of the 2015 Gorkha, Nepal, earthquake (Mw 7.8) were evaluated. The mainshock and aftershocks were recorded continuously by the international Kathmandu strong motion seismographic array operated by Hokkaido University and Tribhuvan University. Full waveform data without saturation for all events enabled us to clarify aftershock locations and decay characteristics. The aftershock distribution was determined using the estimated local velocity structure. The hypocenter distribution in the Kathmandu metropolitan region was well determined and indicated earthquakes located shallower than 12 km depth, suggesting that aftershocks occurred at depths shallower than the Himalayan main thrust fault. Although numerical investigation suggested less resolution for the depth component, the regional aftershock epicentral distribution of the entire focal region clearly indicated earthquakes concentrated in the eastern margin of the major slip region of the mainshock. The calculated modified Omori law's p value of 1.35 suggests rapid aftershock decay and a possible high temperature structure in the aftershock region.

  5. Thermodynamics-based models of transcriptional regulation with gene sequence.

    PubMed

    Wang, Shuqiang; Shen, Yanyan; Hu, Jinxing

    2015-12-01

    Quantitative models of gene regulatory activity have the potential to improve our mechanistic understanding of transcriptional regulation. However, the few models available today have been based on simplistic assumptions about the sequences being modeled or heuristic approximations of the underlying regulatory mechanisms. In this work, we have developed a thermodynamics-based model to predict gene expression driven by any DNA sequence. The proposed model relies on a continuous time, differential equation description of transcriptional dynamics. The sequence features of the promoter are exploited to derive the binding affinity which is derived based on statistical molecular thermodynamics. Experimental results show that the proposed model can effectively identify the activity levels of transcription factors and the regulatory parameters. Comparing with the previous models, the proposed model can reveal more biological sense.

  6. High-Resolution Uitra Low Power, Intergrated Aftershock and Microzonation System

    NASA Astrophysics Data System (ADS)

    Passmore, P.; Zimakov, L. G.

    2012-12-01

    Rapid Aftershock Mobilization plays an essential role in the understanding of both focal mechanism and rupture propagation caused by strong earthquakes. A quick assessment of the data provides a unique opportunity to study the dynamics of the entire earthquake process in-situ. Aftershock study also provides practical information for local authorities regarding the post earthquake activity, which is very important in order to conduct the necessary actions for public safety in the area affected by the strong earthquake. Refraction Technology, Inc. has developed a self-contained, fully integrated Aftershock System, model 160-03, providing the customer simple and quick deployment during aftershock emergency mobilization and microzonation studies. The 160-03 has no external cables or peripheral equipment for command/control and operation in the field. The 160-03 contains three major components integrated in one case: a) 24-bit resolution state-of-the art low power ADC with CPU and Lid interconnect boards; b) power source; and c) three component 2 Hz sensors (two horizontals and one vertical), and built-in ±4g accelerometer. Optionally, the 1 Hz sensors can be built-in the 160-03 system at the customer's request. The self-contained rechargeable battery pack provides power autonomy up to 7 days during data acquisition at 200 sps on continuous three weak motion and triggered three strong motion recording channels. For longer power autonomy, the 160-03 Aftershock System battery pack can be charged from an external source (solar power system). The data in the field is recorded to a built-in swappable USB flash drive. The 160-03 configuration is fixed based on a configuration file stored on the system, so no external command/control interface is required for parameter setup in the field. For visual control of the system performance in the field, the 160-03 has a built-in LED display which indicates the systems recording status as well as a hot swappable USB drive and battery

  7. Aftershock seismicity of the 27 February 2010 Mw 8.8 Maule earthquake rupture zone

    NASA Astrophysics Data System (ADS)

    Lange, Dietrich; Tilmann, Frederik; Barrientos, Sergio E.; Contreras-Reyes, Eduardo; Methe, Pascal; Moreno, Marcos; Heit, Ben; Agurto, Hans; Bernard, Pascal; Vilotte, Jean-Pierre; Beck, Susan

    2012-02-01

    On 27 February 2010 the Mw 8.8 Maule earthquake in Central Chile ruptured a seismic gap where significant strain had accumulated since 1835. Shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity. Here, we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines. By processing the seismic data between 15 March and 30 September 2010 from stations from IRIS, IPGP, GFZ and University of Liverpool we determined 20,205 hypocentres with magnitudes Mw between 1 and 5.5. Seismic activity occurs in six groups: 1.) Normal faulting outer rise events 2.) A shallow group of plate interface seismicity apparent at 25-35 km depth and 50-120 km distance to the trench with some variations between profiles. Along strike, the aftershocks occur largely within the zone of coseismic slip but extend ~ 50 km further north, and with predominantly shallowly dipping thrust mechanisms. Along dip, the events are either within the zone of coseismic slip, or downdip from it, depending on the coseismic slip model used. 3.) A third band of seismicity is observed further downdip at 40-50 km depth and further inland at 150-160 km trench perpendicular distance, with mostly shallow dipping (~ 28°) thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture, and presumably above the intersection of the continental Moho with the plate interface. 4.) A deep group of intermediate depth events between 80 and 120 km depth is present north of 36°S. Within the Maule segment, a large portion of events during the inter-seismic phase originated from this depth range. 5.) The magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the Mw 8.8 Maule 2010 earthquake. 6.) Pronounced crustal aftershock activity

  8. Implication from the aftershocks of the 1989 Loma Prieta earthquake

    SciTech Connect

    Tajima, Fumiko; Sen, M.K. )

    1990-08-01

    The authors examined the P wave displacement spectra of nine aftershocks (M = 2.5{approximately}3.6) of the 1989 Loma Prieta earthquake recorded on PASSCAL/IRIS instruments to search for changes in the spectra that are indicative of heterogeneity in the source region. Temporal variations of spectral characteristics have been observed from the records of two events (No. 7 with M = 2.7 and No. 8 with M = 2.5) that occurred at an almost identical location with a time interval of 16 min and recorded at common stations. The different spectral characteristics can be attributed to the differences in the source time functions of these events. Also, the spectrum of event No. 2 (M = 2.5) that occurred near San Francisco, is substantially richer in high frequency than those from events of a comparable size in the immediate aftershock area. This could be an indication of progressive stress concentration beyond the present aftershock area.

  9. Modeling genome coverage in single-cell sequencing

    PubMed Central

    Daley, Timothy; Smith, Andrew D.

    2014-01-01

    Motivation: Single-cell DNA sequencing is necessary for examining genetic variation at the cellular level, which remains hidden in bulk sequencing experiments. But because they begin with such small amounts of starting material, the amount of information that is obtained from single-cell sequencing experiment is highly sensitive to the choice of protocol employed and variability in library preparation. In particular, the fraction of the genome represented in single-cell sequencing libraries exhibits extreme variability due to quantitative biases in amplification and loss of genetic material. Results: We propose a method to predict the genome coverage of a deep sequencing experiment using information from an initial shallow sequencing experiment mapped to a reference genome. The observed coverage statistics are used in a non-parametric empirical Bayes Poisson model to estimate the gain in coverage from deeper sequencing. This approach allows researchers to know statistical features of deep sequencing experiments without actually sequencing deeply, providing a basis for optimizing and comparing single-cell sequencing protocols or screening libraries. Availability and implementation: The method is available as part of the preseq software package. Source code is available at http://smithlabresearch.org/preseq. Contact: andrewds@usc.edu Supplementary information: Supplementary material is available at Bioinformatics online. PMID:25107873

  10. An ETAS model with varying productivity rates

    NASA Astrophysics Data System (ADS)

    Harte, D. S.

    2014-07-01

    We present an epidemic type aftershock sequenc (ETAS) model where the offspring rates vary both spatially and temporally. This is achieved by distinguishing between those space-time volumes where the interpoint space and time distances are small, and those where they are considerably larger. We also question the nature of the background component in the ETAS model. Is it simply a temporal boundary correction (t = 0) or does it represent an additional tectonic process not described by the aftershock component? The form of these stochastic models should not be considered to be fixed. As we accumulate larger and better earthquake catalogues, GPS data, strain rates, etc., we have the ability to ask more complex questions about the nature of the process. By fitting modified models consistent with such questions, we should gain a better insight into the earthquake process. Hence, we consider a sequence of incrementally modified ETAS type models rather than `the' ETAS model.

  11. The systematic study of the stability of forecasts in the rate- and state-dependent model

    NASA Astrophysics Data System (ADS)

    De Gaetano, D.; McCloskey, J.; Nalbant, S. S.

    2011-12-01

    Numerous observations have shown a general spatial correlation between positive Coulomb failure stress changes due to an earthquake and the locations of aftershocks. However this correlation does not give any indication of the rate from which we can infer the magnitude using the Gutenberg-Richter law. Dieterich's rate- and state-dependent model can be used to obtain a forecast of the observed aftershock rate for the space and time evolution of seismicity caused by stress changes applied to an infinite population of nucleating patches. The seismicity rate changes on this model depend on eight parameters: the stressing rate, the amplitude of the stress perturbation, the physical constitutive properties of faults, the spatial parameters (location and radii of the cells), the start and duration of each of the temporal windows as well as the background seismicity rate. The background seismicity is declustered using the epidemic type aftershock sequence model. We use the 1992 Landers earthquake as a case study, using the Southern California Earthquake Data Centre (SCEDC) catalogue, to examine if Dieterich's rate- and state-dependent model can forecast the aftershock seismicity rate. We perform a systematic study on a range of values on all the parameters to test the forecasting ability of this model. The results obtained suggest variable success in forecasting, when varying the values for the parameters, with the spatial and temporal parameters being the most sensitive. The Omori-Utsu law describes the aftershock rate as a power law in time following the main shock and depends on only three parameters: the aftershock productivity, the elapsed time since the main shock and the constant time shift, all of which can be estimated in the early part of the aftershock sequence and then extrapolated to give a long term rate forecast. All parameters are estimated using maximum likelihood methods. We compare the Dieterich and the Omori-Utsu forecasts using the Akaike information

  12. Foreshock Sequences and Short-Term Earthquake Predictability on East Pacific Rise Transform Faults

    NASA Astrophysics Data System (ADS)

    McGuire, J. J.; Boettcher, M. S.; Jordan, T. H.

    2004-12-01

    A predominant view of continental seismicity postulates that all earthquakes initiate in a similar manner regardless of their eventual size and that earthquake triggering can be described by an Endemic Type Aftershock Sequence (ETAS) model [e.g. Ogata, 1988, Helmstetter and Sorenette 2002]. These null hypotheses cannot be rejected as an explanation for the relative abundances of foreshocks and aftershocks to large earthquakes in California [Helmstetter et al., 2003]. An alternative location for testing this hypothesis is mid-ocean ridge transform faults (RTFs), which have many properties that are distinct from continental transform faults: most plate motion is accommodated aseismically, many large earthquakes are slow events enriched in low-frequency radiation, and the seismicity shows depleted aftershock sequences and high foreshock activity. Here we use the 1996-2001 NOAA-PMEL hydroacoustic seismicity catalog for equatorial East Pacific Rise transform faults to show that the foreshock/aftershock ratio is two orders of magnitude greater than the ETAS prediction based on global RTF aftershock abundances. We can thus reject the null hypothesis that there is no fundamental distinction between foreshocks, mainshocks, and aftershocks on RTFs. We further demonstrate (retrospectively) that foreshock sequences on East Pacific Rise transform faults can be used to achieve statistically significant short-term prediction of large earthquakes (magnitude ≥ 5.4) with good spatial (15-km) and temporal (1-hr) resolution using the NOAA-PMEL catalogs. Our very simplistic approach produces a large number of false alarms, but it successfully predicts the majority (70%) of M≥5.4 earthquakes while covering only a tiny fraction (0.15%) of the total potential space-time volume with alarms. Therefore, it achieves a large probability gain (about a factor of 500) over random guessing, despite not using any near field data. The predictability of large EPR transform earthquakes suggests

  13. Model identification for DNA sequence-structure relationships.

    PubMed

    Hawley, Stephen Dwyer; Chiu, Anita; Chizeck, Howard Jay

    2006-11-01

    We investigate the use of algebraic state-space models for the sequence dependent properties of DNA. By considering the DNA sequence as an input signal, rather than using an all atom physical model, computational efficiency is achieved. A challenge in deriving this type of model is obtaining its structure and estimating its parameters. Here we present two candidate model structures for the sequence dependent structural property Slide and a method of encoding the models so that a recursive least squares algorithm can be applied for parameter estimation. These models are based on the assumption that the value of Slide at a base-step is determined by the surrounding tetranucleotide sequence. The first model takes the four bases individually as inputs and has a median root mean square deviation of 0.90 A. The second model takes the four bases pairwise and has a median root mean square deviation of 0.88 A. These values indicate that the accuracy of these models is within the useful range for structure prediction. Performance is comparable to published predictions of a more physically derived model, at significantly less computational cost.

  14. Mapping Sensorimotor Sequences to Word Sequences: A Connectionist Model of Language Acquisition and Sentence Generation

    ERIC Educational Resources Information Center

    Takac, Martin; Benuskova, Lubica; Knott, Alistair

    2012-01-01

    In this article we present a neural network model of sentence generation. The network has both technical and conceptual innovations. Its main technical novelty is in its semantic representations: the messages which form the input to the network are structured as sequences, so that message elements are delivered to the network one at a time. Rather…

  15. Theoretical modelling of epigenetically modified DNA sequences

    PubMed Central

    Carvalho, Alexandra Teresa Pires; Gouveia, Maria Leonor; Raju Kanna, Charan; Wärmländer, Sebastian K. T. S.; Platts, Jamie; Kamerlin, Shina Caroline Lynn

    2015-01-01

    We report herein a set of calculations designed to examine the effects of epigenetic modifications on the structure of DNA. The incorporation of methyl, hydroxymethyl, formyl and carboxy substituents at the 5-position of cytosine is shown to hardly affect the geometry of CG base pairs, but to result in rather larger changes to hydrogen-bond and stacking binding energies, as predicted by dispersion-corrected density functional theory (DFT) methods. The same modifications within double-stranded GCG and ACA trimers exhibit rather larger structural effects, when including the sugar-phosphate backbone as well as sodium counterions and implicit aqueous solvation. In particular, changes are observed in the buckle and propeller angles within base pairs and the slide and roll values of base pair steps, but these leave the overall helical shape of DNA essentially intact. The structures so obtained are useful as a benchmark of faster methods, including molecular mechanics (MM) and hybrid quantum mechanics/molecular mechanics (QM/MM) methods. We show that previously developed MM parameters satisfactorily reproduce the trimer structures, as do QM/MM calculations which treat bases with dispersion-corrected DFT and the sugar-phosphate backbone with AMBER. The latter are improved by inclusion of all six bases in the QM region, since a truncated model including only the central CG base pair in the QM region is considerably further from the DFT structure. This QM/MM method is then applied to a set of double-stranded DNA heptamers derived from a recent X-ray crystallographic study, whose size puts a DFT study beyond our current computational resources. These data show that still larger structural changes are observed than in base pairs or trimers, leading us to conclude that it is important to model epigenetic modifications within realistic molecular contexts. PMID:26448859

  16. Did stress triggering cause the large off-fault aftershocks of the 25 March 1998 MW=8.1 Antarctic plate earthquake?

    USGS Publications Warehouse

    Toda, S.; Stein, R.S.

    2000-01-01

    The 1998 Antarctic plate earthquake produced clusters of aftershocks (MW ??? 6.4) up to 80 km from the fault rupture and up to 100 km beyond the end of the rupture. Because the mainshock occurred far from the nearest plate boundary and the nearest recorded earthquake, it is unusually isolated from the stress perturbations caused by other earthquakes, making it a good candidate for stress transfer analysis despite the absence of near-field observations. We tested whether the off-fault aftershocks lie in regions brought closer to Coulomb failure by the main rupture. We evaluated four published source models for the main rupture. In fourteen tests using different aftershocks sets and allowing the rupture sources to be shifted within their uncertainties, 6 were significant at ??? 99% confidence, 3 at > 95% confidence, and 5 were not significant (< 95% level). For the 9 successful tests, the stress at the site of the aftershocks was typically increased by 1-2 bars (0.1-0.2 MPa). Thus the Antarctic plate event, together with the 1992 MW=7.3 Landers and its MW=6.5 Big Bear aftershock 40 km from the main fault, supply evidence that small stress changes might indeed trigger large earthquakes far from the main fault rupture.

  17. High resolution earthquake source mechanisms in a subduction zone: 3-D waveform simulations of aftershocks from the 2010 Mw 8.8 Chile rupture

    NASA Astrophysics Data System (ADS)

    Hicks, Stephen; Rietbrock, Andreas

    2015-04-01

    The earthquake rupture process is extremely heterogeneous. For subduction zone earthquakes in particular, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood (e.g. Hayes et al., 2012); however, the nature of slip style along any finer-scale structures remains elusive. Regional earthquake moment tensor (RMT) inversion can shed light on faulting mechanisms. However, many traditional regional moment tensor inversions use simplified (1-D) Earth models (e.g. Agurto et al., 2012; Hayes et al., 2013) that only use the lowest frequency parts of the waveform, which may mask source complexity. As a result, we may have to take care when making small-scale interpretations about the causative fault and its slip style. This situation is compounded further by strong lateral variations in subsurface geology, as well as poor station coverage for recording offshore subduction earthquakes. A formal assessment of the resolving capability of RMT inversions in subduction zones is challenging and the application of 3-D waveform simulation techniques in highly heterogeneous media is needed. We generate 3-D waveform simulations of aftershocks from a large earthquake that struck Chile in 2010. The Mw 8.8 Maule earthquake is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best observed aftershock sequences to date. We therefore have a unique opportunity to compare recorded waveforms with simulated waveforms for many earthquakes, shedding light on the effect of 3-D heterogeneity on source imaging. We perform forward simulations using the spectral element wave propagation code, SPEFEM3D (e.g. Komatitsch et al., 2010) for a set of moderate-sized aftershocks (Mw 4.0-5.5). A detailed knowledge of velocity structure

  18. Analysis of the Petatlan aftershocks: Numbers, energy release, and asperities

    NASA Astrophysics Data System (ADS)

    ValdéS, Carlos; Meyer, Robert P.; ZuñIga, Ramón; Havskov, Jens; Singh, Shri K.

    1982-10-01

    The Petatlan earthquake of March 14, 1979 (Ms = 7.6), occurred between the Middle America trench and the Mexican coast, 15 km southwest of Petatlan, Guerrero, Mexico. From seismograms recorded on smoked paper, FM, and digital tapes, we have identified 255 aftershocks with coda lengths greater than 60 s that occurred 11 hours to 36 days after the main shock. Based on these events, the aftershock epicentral area defined during the period between 11 and 60 hours was about 2000 km2; between 11 hours and 6 days it was about 2400 km2. Although the area grew to 6060 km2 in 36 days, most of the activity was still confined within the area defined after 6 days. This suggests that the smaller aftershock area might represent an asperity. The distribution of events and energy release per unit area confirm the existence of heterogeneity in the aftershock area. Thus our data support the concept of an inhomogeneous rupture area that includes an asperity, as suggested by Chael and Stewart (1982) to account for the differences they computed for the body and surface wave moments from WWSSN data. However, the combination of the moments Reichle et al. (1982) report for body and surface waves from IDA data and the rupture areas reported in this paper results in a solution that is most physically realizable in terms of stress drop and slip. We calculate stress drops of 5 and 15 bars, the former for the average over the entire area, the latter for the asperity, and an average slip of 60 cm for the entire area and 120 cm for the asperity. These values for slip are 30% and 60%, respectively, of the convergence of the Cocos plate relative to the North America plate during the 36-year period between the last two major earthquakes in the Petatlan area. Hypocenters of the aftershocks define a zone about 25 km thick, dipping 15° with an azimuth of N20°E, which is perpendicular to the Middle America trench. Most aftershocks are below the main shock. The b value estimated for aftershocks in the

  19. A new distance measure for model-based sequence clustering.

    PubMed

    García-García, Darío; Parrado Hernández, Emilio; Díaz-de María, Fernando

    2009-07-01

    We review the existing alternatives for defining model-based distances for clustering sequences and propose a new one based on the Kullback-Leibler divergence. This distance is shown to be especially useful in combination with spectral clustering. For improved performance in real-world scenarios, a model selection scheme is also proposed.

  20. Short-term earthquake probabilities during the L'Aquila earthquake sequence in central Italy, 2009

    NASA Astrophysics Data System (ADS)

    Falcone, G.; Murru, M.; Zhuang, J.; Console, R.

    2014-12-01

    We compare the forecasting performance of several statistical models, which are used to describe the occurrence process of earthquakes, in forecasting the short-term earthquake probabilities during the occurrence of the L'Aquila earthquake sequence in central Italy, 2009. These models include the Proximity to Past Earthquakes (PPE) model and different versions of the Epidemic Type Aftershock Sequence (ETAS) model. We used the information gains corresponding to the Poisson and binomial scores to evaluate the performance of these models. It is shown that all ETAS models work better than the PPE model. However, when comparing the different types of the ETAS models, the one with the same fixed exponent coefficient α = 2.3 for both the productivity function and the scaling factor in the spatial response function, performs better in forecasting the active aftershock sequence than the other models with different exponent coefficients when the Poisson score is adopted. These latter models perform only better when a lower magnitude threshold of 2.0 and the binomial score are used. The reason is likely due to the fact that the catalog does not contain an event of magnitude similar to the L'Aquila main shock (Mw 6.3) in the training period (April 16, 2005 to March 15, 2009). In this case the a-value is under-estimated and thus also the forecasted seismicity is underestimated when the productivity function is extrapolated to high magnitudes. These results suggest that the training catalog used for estimating the model parameters should include earthquakes of similar magnitudes as the main shock when forecasting seismicity is during an aftershock sequences.

  1. A sequence-dependent rigid-base model of DNA

    NASA Astrophysics Data System (ADS)

    Gonzalez, O.; Petkevičiutė, D.; Maddocks, J. H.

    2013-02-01

    A novel hierarchy of coarse-grain, sequence-dependent, rigid-base models of B-form DNA in solution is introduced. The hierarchy depends on both the assumed range of energetic couplings, and the extent of sequence dependence of the model parameters. A significant feature of the models is that they exhibit the phenomenon of frustration: each base cannot simultaneously minimize the energy of all of its interactions. As a consequence, an arbitrary DNA oligomer has an intrinsic or pre-existing stress, with the level of this frustration dependent on the particular sequence of the oligomer. Attention is focussed on the particular model in the hierarchy that has nearest-neighbor interactions and dimer sequence dependence of the model parameters. For a Gaussian version of this model, a complete coarse-grain parameter set is estimated. The parameterized model allows, for an oligomer of arbitrary length and sequence, a simple and explicit construction of an approximation to the configuration-space equilibrium probability density function for the oligomer in solution. The training set leading to the coarse-grain parameter set is itself extracted from a recent and extensive database of a large number of independent, atomic-resolution molecular dynamics (MD) simulations of short DNA oligomers immersed in explicit solvent. The Kullback-Leibler divergence between probability density functions is used to make several quantitative assessments of our nearest-neighbor, dimer-dependent model, which is compared against others in the hierarchy to assess various assumptions pertaining both to the locality of the energetic couplings and to the level of sequence dependence of its parameters. It is also compared directly against all-atom MD simulation to assess its predictive capabilities. The results show that the nearest-neighbor, dimer-dependent model can successfully resolve sequence effects both within and between oligomers. For example, due to the presence of frustration, the model can

  2. Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

    USGS Publications Warehouse

    Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

    2004-01-01

    Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

  3. Self-Exciting Point Process Modeling of Conversation Event Sequences

    NASA Astrophysics Data System (ADS)

    Masuda, Naoki; Takaguchi, Taro; Sato, Nobuo; Yano, Kazuo

    Self-exciting processes of Hawkes type have been used to model various phenomena including earthquakes, neural activities, and views of online videos. Studies of temporal networks have revealed that sequences of social interevent times for individuals are highly bursty. We examine some basic properties of event sequences generated by the Hawkes self-exciting process to show that it generates bursty interevent times for a wide parameter range. Then, we fit the model to the data of conversation sequences recorded in company offices in Japan. In this way, we can estimate relative magnitudes of the self excitement, its temporal decay, and the base event rate independent of the self excitation. These variables highly depend on individuals. We also point out that the Hawkes model has an important limitation that the correlation in the interevent times and the burstiness cannot be independently modulated.

  4. Model-Based Obstacle Detention From Image Sequences

    NASA Technical Reports Server (NTRS)

    Sull, Sanghoon; Sridhar, Banavar

    1995-01-01

    This paper proposes a method for detecting obstacles on a runway from monocular image sequences. The surface of the runway is modeled as a plane and the model flow field corresponding to the runway is described by 8 coefficients. The set of 8 coefficients describing the initial model flow field is given by the data from Inertial Navigation System (INS). The uncertainties of this initial model flow field are estimated and used to obtain the accurate model flow field. The residual flow field after warping images by the accurate model flow field is computed by solving over determined gradient-based optical flow equations using a singular value decomposition (SVD). This SVD gives us a new insight of the uncertainties inherent in the optical flow computation. Those pixels with large residual flow vectors are considered as obstacles. Experimental results for two real image sequences are presented.

  5. Motif Yggdrasil: sampling sequence motifs from a tree mixture model.

    PubMed

    Andersson, Samuel A; Lagergren, Jens

    2007-06-01

    In phylogenetic foot-printing, putative regulatory elements are found in upstream regions of orthologous genes by searching for common motifs. Motifs in different upstream sequences are subject to mutations along the edges of the corresponding phylogenetic tree, consequently taking advantage of the tree in the motif search is an appealing idea. We describe the Motif Yggdrasil sampler; the first Gibbs sampler based on a general tree that uses unaligned sequences. Previous tree-based Gibbs samplers have assumed a star-shaped tree or partially aligned upstream regions. We give a probabilistic model (MY model) describing upstream sequences with regulatory elements and build a Gibbs sampler with respect to this model. The model allows toggling, i.e., the restriction of a position to a subset of nucleotides, but does not require aligned sequences nor edge lengths, which may be difficult to come by. We apply the collapsing technique to eliminate the need to sample nuisance parameters, and give a derivation of the predictive update formula. We show that the MY model improves the modeling of difficult motif instances and that the use of the tree achieves a substantial increase in nucleotide level correlation coefficient both for synthetic data and 37 bacterial lexA genes. We investigate the sensitivity to errors in the tree and show that using random trees MY sampler still has a performance similar to the original version.

  6. Generation of animation sequences of three dimensional models

    NASA Technical Reports Server (NTRS)

    Poi, Sharon (Inventor); Bell, Brad N. (Inventor)

    1990-01-01

    The invention is directed toward a method and apparatus for generating an animated sequence through the movement of three-dimensional graphical models. A plurality of pre-defined graphical models are stored and manipulated in response to interactive commands or by means of a pre-defined command file. The models may be combined as part of a hierarchical structure to represent physical systems without need to create a separate model which represents the combined system. System motion is simulated through the introduction of translation, rotation and scaling parameters upon a model within the system. The motion is then transmitted down through the system hierarchy of models in accordance with hierarchical definitions and joint movement limitations. The present invention also calls for a method of editing hierarchical structure in response to interactive commands or a command file such that a model may be included, deleted, copied or moved within multiple system model hierarchies. The present invention also calls for the definition of multiple viewpoints or cameras which may exist as part of a system hierarchy or as an independent camera. The simulated movement of the models and systems is graphically displayed on a monitor and a frame is recorded by means of a video controller. Multiple movement and hierarchy manipulations are then recorded as a sequence of frames which may be played back as an animation sequence on a video cassette recorder.

  7. Main sequence models for massive zero-metal stars

    NASA Technical Reports Server (NTRS)

    Cary, N.

    1974-01-01

    Zero-age main-sequence models for stars of 20, 10, 5, and 2 solar masses with no heavy elements are constructed for three different possible primordial helium abundances: Y=0.00, Y=0.23, and Y=0.30. The latter two values of Y bracket the range of primordial helium abundances cited by Wagoner. With the exceptions of the two 20 solar mass models that contain helium, these models are found to be self-consistent in the sense that the formation of carbon through the triple-alpha process during premain sequence contraction is not sufficient to bring the CN cycle into competition with the proton-proton chain on the ZAMS. The zero-metal models of the present study have higher surface and central temperatures, higher central densities, smaller radii, and smaller convective cores than do the population I models with the same masses.

  8. Evaluation of methods for modeling transcription-factor sequence specificity

    PubMed Central

    Weirauch, Matthew T.; Cote, Atina; Norel, Raquel; Annala, Matti; Zhao, Yue; Riley, Todd R.; Saez-Rodriguez, Julio; Cokelaer, Thomas; Vedenko, Anastasia; Talukder, Shaheynoor; Bussemaker, Harmen J.; Morris, Quaid D.; Bulyk, Martha L.; Stolovitzky, Gustavo

    2013-01-01

    Genomic analyses often involve scanning for potential transcription-factor (TF) binding sites using models of the sequence specificity of DNA binding proteins. Many approaches have been developed to model and learn a protein’s binding specificity, but these methods have not been systematically compared. Here we applied 26 such approaches to in vitro protein binding microarray data for 66 mouse TFs belonging to various families. For 9 TFs, we also scored the resulting motif models on in vivo data, and found that the best in vitro–derived motifs performed similarly to motifs derived from in vivo data. Our results indicate that simple models based on mononucleotide position weight matrices learned by the best methods perform similarly to more complex models for most TFs examined, but fall short in specific cases (<10%). In addition, the best-performing motifs typically have relatively low information content, consistent with widespread degeneracy in eukaryotic TF sequence preferences. PMID:23354101

  9. Generalized Levy-walk model for DNA nucleotide sequences

    NASA Technical Reports Server (NTRS)

    Buldyrev, S. V.; Goldberger, A. L.; Havlin, S.; Simons, M.; Stanley, H. E.

    1993-01-01

    We propose a generalized Levy walk to model fractal landscapes observed in noncoding DNA sequences. We find that this model provides a very close approximation to the empirical data and explains a number of statistical properties of genomic DNA sequences such as the distribution of strand-biased regions (those with an excess of one type of nucleotide) as well as local changes in the slope of the correlation exponent alpha. The generalized Levy-walk model simultaneously accounts for the long-range correlations in noncoding DNA sequences and for the apparently paradoxical finding of long subregions of biased random walks (length lj) within these correlated sequences. In the generalized Levy-walk model, the lj are chosen from a power-law distribution P(lj) varies as lj(-mu). The correlation exponent alpha is related to mu through alpha = 2-mu/2 if 2 < mu < 3. The model is consistent with the finding of "repetitive elements" of variable length interspersed within noncoding DNA.

  10. Model morphing and sequence assignment after molecular replacement.

    PubMed

    Terwilliger, Thomas C; Read, Randy J; Adams, Paul D; Brunger, Axel T; Afonine, Pavel V; Hung, Li-Wei

    2013-11-01

    A procedure termed `morphing' for improving a model after it has been placed in the crystallographic cell by molecular replacement has recently been developed. Morphing consists of applying a smooth deformation to a model to make it match an electron-density map more closely. Morphing does not change the identities of the residues in the chain, only their coordinates. Consequently, if the true structure differs from the working model by containing different residues, these differences cannot be corrected by morphing. Here, a procedure that helps to address this limitation is described. The goal of the procedure is to obtain a relatively complete model that has accurate main-chain atomic positions and residues that are correctly assigned to the sequence. Residues in a morphed model that do not match the electron-density map are removed. Each segment of the resulting trimmed morphed model is then assigned to the sequence of the molecule using information about the connectivity of the chains from the working model and from connections that can be identified from the electron-density map. The procedure was tested by application to a recently determined structure at a resolution of 3.2 Å and was found to increase the number of correctly identified residues in this structure from the 88 obtained using phenix.resolve sequence assignment alone (Terwilliger, 2003) to 247 of a possible 359. Additionally, the procedure was tested by application to a series of templates with sequence identities to a target structure ranging between 7 and 36%. The mean fraction of correctly identified residues in these cases was increased from 33% using phenix.resolve sequence assignment to 47% using the current procedure. The procedure is simple to apply and is available in the Phenix software package.

  11. A mathematical model and numerical method for thermoelectric DNA sequencing

    NASA Astrophysics Data System (ADS)

    Shi, Liwei; Guilbeau, Eric J.; Nestorova, Gergana; Dai, Weizhong

    2014-05-01

    Single nucleotide polymorphisms (SNPs) are single base pair variations within the genome that are important indicators of genetic predisposition towards specific diseases. This study explores the feasibility of SNP detection using a thermoelectric sequencing method that measures the heat released when DNA polymerase inserts a deoxyribonucleoside triphosphate into a DNA strand. We propose a three-dimensional mathematical model that governs the DNA sequencing device with a reaction zone that contains DNA template/primer complex immobilized to the surface of the lower channel wall. The model is then solved numerically. Concentrations of reactants and the temperature distribution are obtained. Results indicate that when the nucleoside is complementary to the next base in the DNA template, polymerization occurs lengthening the complementary polymer and releasing thermal energy with a measurable temperature change, implying that the thermoelectric conceptual device for sequencing DNA may be feasible for identifying specific genes in individuals.

  12. Matched-filter Detection of the Missing Foreshocks and Aftershocks of the 2015 Gorkha earthquake

    NASA Astrophysics Data System (ADS)

    Meng, L.; Huang, H.; Wang, Y.; Plasencia Linares, M. P.

    2015-12-01

    The 25 April 2015 Mw 7.8 Gorkha earthquake occurred at the bottom edge of the locking portion of the Main Himalayan Thrust (MHT), where the Indian plate under-thrusts the Himalayan wedge. The earthquake is followed by a number of large aftershocks but is not preceded by any foreshocks within ~3 weeks according to the NEIC, ISC and NSC catalog. However, a large portion of aftershocks could be missed due to either the contamination of the mainshock coda or small signal to noise ratio. It is also unclear whether there are foreshocks preceding the mainshock, the underlying physical processes of which are crucial for imminent seismic hazard assessment. Here, we employ the matched filter technique to recover the missing events from 22 April to 30 April. We collect 3-component broadband seismic waveforms recorded by one station in Nepal operated by Ev-K2-CNR, OGS Italy and eleven stations in Tibet operated by the China Earthquake Networks Center. We bandpass the seismograms to 1-6 Hz to retain high frequency energies. The template waveforms with high signal-to-noise ratios (> 5) are obtained at several closest stations. To detect and locate the events that occur around the templates, correlograms are shifted at each station with differential travel time as a function of source location based on the CRUST1.0 model. We find ~14 times more events than those listed in the ISC catalog. Some of the detected events are confirmed by visual inspections of the waveforms at the closest stations. The preliminary results show a streak of seismicity occurred around 2.5 days before the mainshock to the southeast of the mainshock hypocenter. The seismicity rate is elevated above the background level during this period of time and decayed subsequently following the Omori's law. The foreshocks appear to migrate towards the hypocenter with logarithmic time ahead of the mainshock, which indicates possible triggering of the mainshock by the propagating afterslip of the foreshocks. Immediately

  13. Relocation and characteristics of recent earthquake sequences (2013, 2014) on the North Gulf of Evia, Greece

    NASA Astrophysics Data System (ADS)

    Moshou, Alexandra; Ganas, Athanassios; Karastathis, Vassilios; Mouzakiotis, Evangelos

    2015-04-01

    This work presents the results of relocation and stress inversion analysis for two recent earthquake sequences in the northern Gulf of Evia, central Greece. On 12 November 2013 (18:09, UTC) a moderate earthquake, ML=4.8 occurred onshore northern Evia, near the village Taxiarxis. The epicentral area of this event was manually located: φ=38.9133° Ν, λ=23.0977° Ε at depth 14 km, according to NOA. For a period of one month there were 155 aftershocks with magnitude ML>0.5, while the first day there were 85 earthquakes; the largest of them with magnitude ML=3.9. On November 17, 2014, two shallow earthquakes with magnitude ML=5.2 occurred inside the northern Gulf of Evia, about 34 km NW of Chalkis town. For the location of above events broadband data from HUSN network were used. The relocation for both sequences was done by use of the NonLinLoc software of Lomax etal. (2000). For this purpose a local velocity model was used, calculated in the past by traveltime inversion techniques. For the 2013 seismic sequence the phase data from National Observatory of Athens include more than 12700 P and 4800 S - wave arrivals. Only events with at least 8 P-wave and 4 S-wave arrival having an azimuthal gap lower than 180°, location RMS lower than 0.8 sec and vertical and horizontal errors lower than 1.5 km were selected for processing. A NNW-SSE near-vertical fault was revealed after relocation. The second part of this study refers to the calculation of the moment tensor solutions for the main events as well as for the strongest aftershocks of the 2014 seismic sequence. Seismological broadband data from the Hellenic Unified Seismological Network were collected and analyzed in order to determine the source parameters of the events that occurred in the study area. We selected and analyzed the data of 10 broadband seismological stations with three components. The source parameters were calculated based on a moment tensor inversion, using regional waveforms at epicentral distances

  14. Extracting protein alignment models from the sequence database.

    PubMed Central

    Neuwald, A F; Liu, J S; Lipman, D J; Lawrence, C E

    1997-01-01

    Biologists often gain structural and functional insights into a protein sequence by constructing a multiple alignment model of the family. Here a program called Probe fully automates this process of model construction starting from a single sequence. Central to this program is a powerful new method to locate and align only those, often subtly, conserved patterns essential to the family as a whole. When applied to randomly chosen proteins, Probe found on average about four times as many relationships as a pairwise search and yielded many new discoveries. These include: an obscure subfamily of globins in the roundworm Caenorhabditis elegans ; two new superfamilies of metallohydrolases; a lipoyl/biotin swinging arm domain in bacterial membrane fusion proteins; and a DH domain in the yeast Bud3 and Fus2 proteins. By identifying distant relationships and merging families into superfamilies in this way, this analysis further confirms the notion that proteins evolved from relatively few ancient sequences. Moreover, this method automatically generates models of these ancient conserved regions for rapid and sensitive screening of sequences. PMID:9108146

  15. SOME NEW PROCESSING TECHNIQUES FOR THE IMPERIAL VALLEY 1979 AFTERSHOCKS.

    USGS Publications Warehouse

    Brady, A. Gerald; ,

    1983-01-01

    This paper describes some of the features of the latest processing improvements that the U. S. Geological Survey (USGS) is currently applying to strong-motion accelerograms from the national network of permanent stations. At the same time it introduces the application of this processing to the set of Imperial Valley aftershocks recorded following the main shock of October 15, 1979. Earlier processing of the 22 main shock recordings provided corrected accelerations, velocity and displacement, response spectra, and Fourier spectra.

  16. Probabilistic model based error correction in a set of various mutant sequences analyzed by next-generation sequencing.

    PubMed

    Aita, Takuyo; Ichihashi, Norikazu; Yomo, Tetsuya

    2013-12-01

    To analyze the evolutionary dynamics of a mutant population in an evolutionary experiment, it is necessary to sequence a vast number of mutants by high-throughput (next-generation) sequencing technologies, which enable rapid and parallel analysis of multikilobase sequences. However, the observed sequences include many errors of base call. Therefore, if next-generation sequencing is applied to analysis of a heterogeneous population of various mutant sequences, it is necessary to discriminate between true bases as point mutations and errors of base call in the observed sequences, and to subject the sequences to error-correction processes. To address this issue, we have developed a novel method of error correction based on the Potts model and a maximum a posteriori probability (MAP) estimate of its parameters corresponding to the "true sequences". Our method of error correction utilizes (1) the "quality scores" which are assigned to individual bases in the observed sequences and (2) the neighborhood relationship among the observed sequences mapped in sequence space. The computer experiments of error correction of artificially generated sequences supported the effectiveness of our method, showing that 50-90% of errors were removed. Interestingly, this method is analogous to a probabilistic model based method of image restoration developed in the field of information engineering.

  17. Genome sequencing and analysis of the model grass Brachypodium distachyon.

    PubMed

    2010-02-11

    Three subfamilies of grasses, the Ehrhartoideae, Panicoideae and Pooideae, provide the bulk of human nutrition and are poised to become major sources of renewable energy. Here we describe the genome sequence of the wild grass Brachypodium distachyon (Brachypodium), which is, to our knowledge, the first member of the Pooideae subfamily to be sequenced. Comparison of the Brachypodium, rice and sorghum genomes shows a precise history of genome evolution across a broad diversity of the grasses, and establishes a template for analysis of the large genomes of economically important pooid grasses such as wheat. The high-quality genome sequence, coupled with ease of cultivation and transformation, small size and rapid life cycle, will help Brachypodium reach its potential as an important model system for developing new energy and food crops.

  18. Genome sequencing and analysis of the model grass Brachypodium distachyon

    SciTech Connect

    Yang, Xiaohan; Kalluri, Udaya C; Tuskan, Gerald A

    2010-01-01

    Three subfamilies of grasses, the Ehrhartoideae, Panicoideae and Pooideae, provide the bulk of human nutrition and are poised to become major sources of renewable energy. Here we describe the genome sequence of the wild grass Brachypodium distachyon (Brachypodium), which is, to our knowledge, the first member of the Pooideae subfamily to be sequenced. Comparison of the Brachypodium, rice and sorghum genomes shows a precise history of genome evolution across a broad diversity of the grasses, and establishes a template for analysis of the large genomes of economically important pooid grasses such as wheat. The high-quality genome sequence, coupled with ease of cultivation and transformation, small size and rapid life cycle, will help Brachypodium reach its potential as an important model system for developing new energy and food crops.

  19. Genome sequence of the model medicinal mushroom Ganoderma lucidum

    PubMed Central

    Chen, Shilin; Xu, Jiang; Liu, Chang; Zhu, Yingjie; Nelson, David R.; Zhou, Shiguo; Li, Chunfang; Wang, Lizhi; Guo, Xu; Sun, Yongzhen; Luo, Hongmei; Li, Ying; Song, Jingyuan; Henrissat, Bernard; Levasseur, Anthony; Qian, Jun; Li, Jianqin; Luo, Xiang; Shi, Linchun; He, Liu; Xiang, Li; Xu, Xiaolan; Niu, Yunyun; Li, Qiushi; Han, Mira V.; Yan, Haixia; Zhang, Jin; Chen, Haimei; Lv, Aiping; Wang, Zhen; Liu, Mingzhu; Schwartz, David C.; Sun, Chao

    2012-01-01

    Ganoderma lucidum is a widely used medicinal macrofungus in traditional Chinese medicine that creates a diverse set of bioactive compounds. Here we report its 43.3-Mb genome, encoding 16,113 predicted genes, obtained using next-generation sequencing and optical mapping approaches. The sequence analysis reveals an impressive array of genes encoding cytochrome P450s (CYPs), transporters and regulatory proteins that cooperate in secondary metabolism. The genome also encodes one of the richest sets of wood degradation enzymes among all of the sequenced basidiomycetes. In all, 24 physical CYP gene clusters are identified. Moreover, 78 CYP genes are coexpressed with lanosterol synthase, and 16 of these show high similarity to fungal CYPs that specifically hydroxylate testosterone, suggesting their possible roles in triterpenoid biosynthesis. The elucidation of the G. lucidum genome makes this organism a potential model system for the study of secondary metabolic pathways and their regulation in medicinal fungi. PMID:22735441

  20. Sequence alignments and pair hidden Markov models using evolutionary history.

    PubMed

    Knudsen, Bjarne; Miyamoto, Michael M

    2003-10-17

    This work presents a novel pairwise statistical alignment method based on an explicit evolutionary model of insertions and deletions (indels). Indel events of any length are possible according to a geometric distribution. The geometric distribution parameter, the indel rate, and the evolutionary time are all maximum likelihood estimated from the sequences being aligned. Probability calculations are done using a pair hidden Markov model (HMM) with transition probabilities calculated from the indel parameters. Equations for the transition probabilities make the pair HMM closely approximate the specified indel model. The method provides an optimal alignment, its likelihood, the likelihood of all possible alignments, and the reliability of individual alignment regions. Human alpha and beta-hemoglobin sequences are aligned, as an illustration of the potential utility of this pair HMM approach.

  1. Direct test of static stress versus dynamic stress triggering of aftershocks

    USGS Publications Warehouse

    Pollitz, F.F.; Johnston, M.J.S.

    2006-01-01

    Aftershocks observed over time scales of minutes to months following a main shock are plausibly triggered by the static stress change imparted by the main shock, dynamic shaking effects associated with passage of seismic waves from the main shock, or a combination of the two. We design a direct test of static versus dynamic triggering of aftershocks by comparing the near-field temporal aftershock patterns generated by aseismic and impulsive events occurring in the same source area. The San Juan Bautista, California, area is ideally suited for this purpose because several events of both types of M???5 have occurred since 1974. We find that aftershock rates observed after impulsive events are much higher than those observed after aseismic events, and this pattern persists for several weeks after the event. This suggests that, at least in the near field, dynamic triggering is the dominant cause of aftershocks, and that it generates both immediate and delayed aftershock activity.

  2. Design of multispecific protein sequences using probabilistic graphical modeling.

    PubMed

    Fromer, Menachem; Yanover, Chen; Linial, Michal

    2010-02-15

    In nature, proteins partake in numerous protein- protein interactions that mediate their functions. Moreover, proteins have been shown to be physically stable in multiple structures, induced by cellular conditions, small ligands, or covalent modifications. Understanding how protein sequences achieve this structural promiscuity at the atomic level is a fundamental step in the drug design pipeline and a critical question in protein physics. One way to investigate this subject is to computationally predict protein sequences that are compatible with multiple states, i.e., multiple target structures or binding to distinct partners. The goal of engineering such proteins has been termed multispecific protein design. We develop a novel computational framework to efficiently and accurately perform multispecific protein design. This framework utilizes recent advances in probabilistic graphical modeling to predict sequences with low energies in multiple target states. Furthermore, it is also geared to specifically yield positional amino acid probability profiles compatible with these target states. Such profiles can be used as input to randomly bias high-throughput experimental sequence screening techniques, such as phage display, thus providing an alternative avenue for elucidating the multispecificity of natural proteins and the synthesis of novel proteins with specific functionalities. We prove the utility of such multispecific design techniques in better recovering amino acid sequence diversities similar to those resulting from millions of years of evolution. We then compare the approaches of prediction of low energy ensembles and of amino acid profiles and demonstrate their complementarity in providing more robust predictions for protein design.

  3. Sequence design in lattice models by graph theoretical methods

    NASA Astrophysics Data System (ADS)

    Sanjeev, B. S.; Patra, S. M.; Vishveshwara, S.

    2001-01-01

    A general strategy has been developed based on graph theoretical methods, for finding amino acid sequences that take up a desired conformation as the native state. This problem of inverse design has been addressed by assigning topological indices for the monomer sites (vertices) of the polymer on a 3×3×3 cubic lattice. This is a simple design strategy, which takes into account only the topology of the target protein and identifies the best sequence for a given composition. The procedure allows the design of a good sequence for a target native state by assigning weights for the vertices on a lattice site in a given conformation. It is seen across a variety of conformations that the predicted sequences perform well both in sequence and in conformation space, in identifying the target conformation as native state for a fixed composition of amino acids. Although the method is tested in the framework of the HP model [K. F. Lau and K. A. Dill, Macromolecules 22, 3986 (1989)] it can be used in any context if proper potential functions are available, since the procedure derives unique weights for all the sites (vertices, nodes) of the polymer chain of a chosen conformation (graph).

  4. Accident sequence precursor analysis level 2/3 model development

    SciTech Connect

    Lui, C.H.; Galyean, W.J.; Brownson, D.A.

    1997-02-01

    The US Nuclear Regulatory Commission`s Accident Sequence Precursor (ASP) program currently uses simple Level 1 models to assess the conditional core damage probability for operational events occurring in commercial nuclear power plants (NPP). Since not all accident sequences leading to core damage will result in the same radiological consequences, it is necessary to develop simple Level 2/3 models that can be used to analyze the response of the NPP containment structure in the context of a core damage accident, estimate the magnitude of the resulting radioactive releases to the environment, and calculate the consequences associated with these releases. The simple Level 2/3 model development work was initiated in 1995, and several prototype models have been completed. Once developed, these simple Level 2/3 models are linked to the simple Level 1 models to provide risk perspectives for operational events. This paper describes the methods implemented for the development of these simple Level 2/3 ASP models, and the linkage process to the existing Level 1 models.

  5. Efficient inference of hidden Markov models from large observation sequences

    NASA Astrophysics Data System (ADS)

    Priest, Benjamin W.; Cybenko, George

    2016-05-01

    The hidden Markov model (HMM) is widely used to model time series data. However, the conventional Baum- Welch algorithm is known to perform poorly when applied to long observation sequences. The literature contains several alternatives that seek to improve the memory or time complexity of the algorithm. However, for an HMM with N states and an observation sequence of length T, these alternatives require at best O(N) space and O(N2T) time. Given the preponderance of applications that increasingly deal with massive amounts of data, an alternative whose time is O(T)+poly(N) is desired. Recent research presents an alternative to the Baum-Welch algorithm that relies on nonnegative matrix factorization. This document examines the space complexity of this alternative approach and proposes further optimizations using approaches adopted from the matrix sketching literature. The result is a streaming algorithm whose space complexity is constant and time complexity is linear with respect to the size of the observation sequence. The paper also presents a batch algorithm that allow for even further improved space complexity at the expense of an additional pass over the observation sequence.

  6. Double-difference Relocation of the Aftershocks of the Tecomán, Colima, Mexico Earthquake of 22 January 2003

    NASA Astrophysics Data System (ADS)

    Andrews, Vanessa; Stock, Joann; Ramírez Vázquez, Carlos Ariel; Reyes-Dávila, Gabriel

    2011-08-01

    On 22 January 2003, the M w = 7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0 km in depth and 1.4 km in the north-south and east-west directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8 km in depth, 0.3 km in the east-west direction, and 0.7 km in the north-south direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3 months after the mainshock.

  7. Simulating Next-Generation Sequencing Datasets from Empirical Mutation and Sequencing Models

    PubMed Central

    Stephens, Zachary D.; Hudson, Matthew E.; Mainzer, Liudmila S.; Taschuk, Morgan; Weber, Matthew R.; Iyer, Ravishankar K.

    2016-01-01

    An obstacle to validating and benchmarking methods for genome analysis is that there are few reference datasets available for which the “ground truth” about the mutational landscape of the sample genome is known and fully validated. Additionally, the free and public availability of real human genome datasets is incompatible with the preservation of donor privacy. In order to better analyze and understand genomic data, we need test datasets that model all variants, reflecting known biology as well as sequencing artifacts. Read simulators can fulfill this requirement, but are often criticized for limited resemblance to true data and overall inflexibility. We present NEAT (NExt-generation sequencing Analysis Toolkit), a set of tools that not only includes an easy-to-use read simulator, but also scripts to facilitate variant comparison and tool evaluation. NEAT has a wide variety of tunable parameters which can be set manually on the default model or parameterized using real datasets. The software is freely available at github.com/zstephens/neat-genreads. PMID:27893777

  8. Accident Sequence Precursor Program Large Early Release Frequency Model Development

    SciTech Connect

    Brown, T.D.; Brownson, D.A.; Duran, F.A.; Gregory, J.J.; Rodrick, E.G.

    1999-01-04

    The objectives for the ASP large early release frequency (LERF) model development work is to build a Level 2 containment response model that would capture all of the events necessary to define LERF as outlined in Regulatory Guide 1.174, can be directly interfaced with the existing Level 1 models, is technically correct, can be readily modified to incorporate new information or to represent another plant, and can be executed in SAPHIRE. The ASP LERF models being developed will meet these objectives while providing the NRC with the capability to independently assess the risk impact of plant-specific changes proposed by the utilities that change the nuclear power plants' licensing basis. Together with the ASP Level 1 models, the ASP LERF models provide the NRC with the capability of performing equipment and event assessments to determine their impact on a plant's LERF for internal events during power operation. In addition, the ASP LERF models are capable of being updated to reflect changes in information regarding the system operations and phenomenological events, and of being updated to assess the potential for early fatalities for each LERF sequence. As the ASP Level 1 models evolve to include more analysis capabilities, the LERF models will also be refined to reflect the appropriate level of detail needed to demonstrate the new capabilities. An approach was formulated for the development of detailed LERF models using the NUREG-1150 APET models as a guide. The modifications to the SAPHIRE computer code have allowed the development of these detailed models and the ability to analyze these models in a reasonable time. Ten reference LERF plant models, including six PWR models and four BWR models, which cover a wide variety of containment and nuclear steam supply systems designs, will be complete in 1999. These reference models will be used as the starting point for developing the LERF models for the remaining nuclear power plants.

  9. Assessing site-interdependent phylogenetic models of sequence evolution.

    PubMed

    Rodrigue, Nicolas; Philippe, Hervé; Lartillot, Nicolas

    2006-09-01

    In recent works, methods have been proposed for applying phylogenetic models that allow for a general interdependence between the amino acid positions of a protein. As of yet, such models have focused on site interdependencies resulting from sequence-structure compatibility constraints, using simplified structural representations in combination with a set of statistical potentials. This structural compatibility criterion is meant as a proxy for sequence fitness, and the methods developed thus far can incorporate different site-interdependent fitness proxies based on other measurements. However, no methods have been proposed for comparing and evaluating the adequacy of alternative fitness proxies in this context, or for more general comparisons with canonical models of protein evolution. In the present work, we apply Bayesian methods of model selection-based on numerical calculations of marginal likelihoods and posterior predictive checks-to evaluate models encompassing the site-interdependent framework. Our application of these methods indicates that considering site-interdependencies, as done here, leads to an improved model fit for all data sets studied. Yet, we find that the use of pairwise contact potentials alone does not suitably account for across-site rate heterogeneity or amino acid exchange propensities; for such complexities, site-independent treatments are still called for. The most favored models combine the use of statistical potentials with a suitably rich site-independent model. Altogether, the methodology employed here should allow for a more rigorous and systematic exploration of different ways of modeling explicit structural constraints, or any other site-interdependent criterion, while best exploiting the richness of previously proposed models.

  10. Evolutionary Sequence Modeling for Discovery of Peptide Hormones

    PubMed Central

    Sonmez, Kemal; Zaveri, Naunihal T.; Kerman, Ilan A.; Burke, Sharon; Neal, Charles R.; Xie, Xinmin; Watson, Stanley J.; Toll, Lawrence

    2009-01-01

    There are currently a large number of “orphan” G-protein-coupled receptors (GPCRs) whose endogenous ligands (peptide hormones) are unknown. Identification of these peptide hormones is a difficult and important problem. We describe a computational framework that models spatial structure along the genomic sequence simultaneously with the temporal evolutionary path structure across species and show how such models can be used to discover new functional molecules, in particular peptide hormones, via cross-genomic sequence comparisons. The computational framework incorporates a priori high-level knowledge of structural and evolutionary constraints into a hierarchical grammar of evolutionary probabilistic models. This computational method was used for identifying novel prohormones and the processed peptide sites by producing sequence alignments across many species at the functional-element level. Experimental results with an initial implementation of the algorithm were used to identify potential prohormones by comparing the human and non-human proteins in the Swiss-Prot database of known annotated proteins. In this proof of concept, we identified 45 out of 54 prohormones with only 44 false positives. The comparison of known and hypothetical human and mouse proteins resulted in the identification of a novel putative prohormone with at least four potential neuropeptides. Finally, in order to validate the computational methodology, we present the basic molecular biological characterization of the novel putative peptide hormone, including its identification and regional localization in the brain. This species comparison, HMM-based computational approach succeeded in identifying a previously undiscovered neuropeptide from whole genome protein sequences. This novel putative peptide hormone is found in discreet brain regions as well as other organs. The success of this approach will have a great impact on our understanding of GPCRs and associated pathways and help to

  11. A stochastic model for EEG microstate sequence analysis.

    PubMed

    Gärtner, Matthias; Brodbeck, Verena; Laufs, Helmut; Schneider, Gaby

    2015-01-01

    The analysis of spontaneous resting state neuronal activity is assumed to give insight into the brain function. One noninvasive technique to study resting state activity is electroencephalography (EEG) with a subsequent microstate analysis. This technique reduces the recorded EEG signal to a sequence of prototypical topographical maps, which is hypothesized to capture important spatio-temporal properties of the signal. In a statistical EEG microstate analysis of healthy subjects in wakefulness and three stages of sleep, we observed a simple structure in the microstate transition matrix. It can be described with a first order Markov chain in which the transition probability from the current state (i.e., map) to a different map does not depend on the current map. The resulting transition matrix shows a high agreement with the observed transition matrix, requiring only about 2% of mass transport (1/2 L1-distance). In the second part, we introduce an extended framework in which the simple Markov chain is used to make inferences on a potential underlying time continuous process. This process cannot be directly observed and is therefore usually estimated from discrete sampling points of the EEG signal given by the local maxima of the global field power. Therefore, we propose a simple stochastic model called sampled marked intervals (SMI) model that relates the observed sequence of microstates to an assumed underlying process of background intervals and thus, complements approaches that focus on the analysis of observable microstate sequences.

  12. Seismic tomography of the area of the 2010 Beni-Ilmane earthquake sequence, north-central Algeria.

    PubMed

    Abacha, Issam; Koulakov, Ivan; Semmane, Fethi; Yelles-Chaouche, Abd Karim

    2014-01-01

    The region of Beni-Ilmane (District of M'sila, north-central Algeria) was the site of an earthquake sequence that started on 14 May 2010. This sequence, which lasted several months, was triggered by conjugate E-W reverse and N-S dextral faulting. To image the crustal structure of these active faults, we used a set of 1406 well located aftershocks events and applied the local tomography software (LOTOS) algorithm, which includes absolute source location, optimization of the initial 1D velocity model, and iterative tomographic inversion for 3D seismic P- and S-wave velocities (and the Vp/Vs ratio), and source parameters. The patterns of P-wave low-velocity anomalies correspond to the alignments of faults determined from geological evidence, and the P-wave high-velocity anomalies may represent rigid blocks of the upper crust that are not deformed by regional stresses. The S-wave low-velocity anomalies coincide with the aftershock area, where relatively high values of Vp/Vs ratio (1.78) are observed compared with values in the surrounding areas (1.62-1.66). These high values may indicate high fluid contents in the aftershock area. These fluids could have been released from deeper levels by fault movements during earthquakes and migrated rapidly upwards. This hypothesis is supported by vertical sections across the study area show that the major Vp/Vs anomalies are located above the seismicity clusters.

  13. MODELING THE RED SEQUENCE: HIERARCHICAL GROWTH YET SLOW LUMINOSITY EVOLUTION

    SciTech Connect

    Skelton, Rosalind E.; Bell, Eric F.; Somerville, Rachel S.

    2012-07-01

    We explore the effects of mergers on the evolution of massive early-type galaxies by modeling the evolution of their stellar populations in a hierarchical context. We investigate how a realistic red sequence population set up by z {approx} 1 evolves under different assumptions for the merger and star formation histories, comparing changes in color, luminosity, and mass. The purely passive fading of existing red sequence galaxies, with no further mergers or star formation, results in dramatic changes at the bright end of the luminosity function and color-magnitude relation. Without mergers there is too much evolution in luminosity at a fixed space density compared to observations. The change in color and magnitude at a fixed mass resembles that of a passively evolving population that formed relatively recently, at z {approx} 2. Mergers among the red sequence population ('dry mergers') occurring after z = 1 build up mass, counteracting the fading of the existing stellar populations to give smaller changes in both color and luminosity for massive galaxies. By allowing some galaxies to migrate from the blue cloud onto the red sequence after z = 1 through gas-rich mergers, younger stellar populations are added to the red sequence. This manifestation of the progenitor bias increases the scatter in age and results in even smaller changes in color and luminosity between z = 1 and z = 0 at a fixed mass. The resultant evolution appears much slower, resembling the passive evolution of a population that formed at high redshift (z {approx} 3-5), and is in closer agreement with observations. We conclude that measurements of the luminosity and color evolution alone are not sufficient to distinguish between the purely passive evolution of an old population and cosmologically motivated hierarchical growth, although these scenarios have very different implications for the mass growth of early-type galaxies over the last half of cosmic history.

  14. Space time ETAS models and an improved extension

    NASA Astrophysics Data System (ADS)

    Ogata, Yosihiko; Zhuang, Jiancang

    2006-02-01

    For sensitive detection of anomalous seismicity such as quiescence and activation in a given region, we need a suitable statistical reference model that represents a normal seismic activity in the region. The regional occurrence rate of the earthquakes is modeled as a function of previous activity, the specific form of which is based on empirical laws in time and space such as the modified Omori formula and the Utsu-Seki scaling law of aftershock area against magnitude, respectively. This manuscript summarizes the development of the epidemic type aftershock sequence (ETAS) model and proposes an extended version of the best fitted space-time model that was suggested in Ogata [Ogata, Y., 1998. Space-time point-process models for earthquake occurrences, Ann. Inst. Statist. Math., 50: 379-402.]. This model indicates significantly better fit to seismicity in various regions in and around Japan.

  15. Modeling seismic swarms triggered by aseismic transients

    NASA Astrophysics Data System (ADS)

    Llenos, Andrea L.; McGuire, Jeffrey J.; Ogata, Yosihiko

    2009-04-01

    The rate of earthquake occurrence varies by many orders of magnitude in a given region due to variations in the stress state of the crust. Our focus here is on variations in seismicity rate triggered by transient aseismic processes such as fluid flow, fault creep or magma intrusion. While these processes have been shown to trigger earthquakes, converting observed seismicity variations into estimates of stress rate variations has been challenging. Essentially aftershock sequences often obscure changes in the background seismicity rate resulting from aseismic processes. Two common approaches for estimating the time dependence of the underlying driving mechanisms are the stochastic Epidemic Type Aftershock Sequence model (ETAS) [Ogata, Y., (1988), Statistical models for earthquake occurrences and residual analysis for point processes, J. Am. Stat. Assoc., 83, 9-27.] and a physical approach based on the rate- and state-model of fault friction [Dieterich, J., (1994), A constitutive law for rate of earthquake production and its application to earthquake clustering, J. Geophys. Res., 99, 2601-2618.]. The models have different strengths that could be combined to allow more quantitative studies of earthquake triggering. To accomplish this, we identify the parameters that relate to one another in the two models and examine their dependence on stressing rate. A particular conflict arises because the rate-state model predicts that aftershock productivity scales with stressing rate while the ETAS model assumes that it is time independent. To resolve this issue, we estimate triggering parameters for 4 earthquake swarms contemporaneous with geodetically observed deformation transients in various tectonic environments. We find that stressing rate transients increase the background seismicity rate without affecting aftershock productivity. We then specify a combined model for seismicity rate variations that will allow future studies to invert seismicity catalogs for variations in

  16. Estimating ETAS: The effects of truncation, missing data, and model assumptions

    NASA Astrophysics Data System (ADS)

    Seif, Stefanie; Mignan, Arnaud; Zechar, Jeremy Douglas; Werner, Maximilian Jonas; Wiemer, Stefan

    2017-01-01

    The Epidemic-Type Aftershock Sequence (ETAS) model is widely used to describe the occurrence of earthquakes in space and time, but there has been little discussion dedicated to the limits of, and influences on, its estimation. Among the possible influences we emphasize in this article the effect of the cutoff magnitude, Mcut, above which parameters are estimated; the finite length of earthquake catalogs; and missing data (e.g., during lively aftershock sequences). We analyze catalogs from Southern California and Italy and find that some parameters vary as a function of Mcut due to changing sample size (which affects, e.g., Omori's c constant) or an intrinsic dependence on Mcut (as Mcut increases, absolute productivity and background rate decrease). We also explore the influence of another form of truncation—the finite catalog length—that can bias estimators of the branching ratio. Being also a function of Omori's p value, the true branching ratio is underestimated by 45% to 5% for 1.05 < p < 1.2. Finite sample size affects the variation of the branching ratio estimates. Moreover, we investigate the effect of missing aftershocks and find that the ETAS productivity parameters (α and K0) and the Omori's c and p values are significantly changed for Mcut < 3.5. We further find that conventional estimation errors for these parameters, inferred from simulations that do not account for aftershock incompleteness, are underestimated by, on average, a factor of 8.

  17. Advanced accident sequence precursor analysis level 2 models

    SciTech Connect

    Galyean, W.J.; Brownson, D.A.; Rempe, J.L.

    1996-03-01

    The U.S. Nuclear Regulatory Commission Accident Sequence Precursor program pursues the ultimate objective of performing risk significant evaluations on operational events (precursors) occurring in commercial nuclear power plants. To achieve this objective, the Office of Nuclear Regulatory Research is supporting the development of simple probabilistic risk assessment models for all commercial nuclear power plants (NPP) in the U.S. Presently, only simple Level 1 plant models have been developed which estimate core damage frequencies. In order to provide a true risk perspective, the consequences associated with postulated core damage accidents also need to be considered. With the objective of performing risk evaluations in an integrated and consistent manner, a linked event tree approach which propagates the front end results to back end was developed. This approach utilizes simple plant models that analyze the response of the NPP containment structure in the context of a core damage accident, estimate the magnitude and timing of a radioactive release to the environment, and calculate the consequences for a given release. Detailed models and results from previous studies, such as the NUREG-1150 study, are used to quantify these simple models. These simple models are then linked to the existing Level 1 models, and are evaluated using the SAPHIRE code. To demonstrate the approach, prototypic models have been developed for a boiling water reactor, Peach Bottom, and a pressurized water reactor, Zion.

  18. PyMod: sequence similarity searches, multiple sequence-structure alignments, and homology modeling within PyMOL

    PubMed Central

    2012-01-01

    Background In recent years, an exponential growing number of tools for protein sequence analysis, editing and modeling tasks have been put at the disposal of the scientific community. Despite the vast majority of these tools have been released as open source software, their deep learning curves often discourages even the most experienced users. Results A simple and intuitive interface, PyMod, between the popular molecular graphics system PyMOL and several other tools (i.e., [PSI-]BLAST, ClustalW, MUSCLE, CEalign and MODELLER) has been developed, to show how the integration of the individual steps required for homology modeling and sequence/structure analysis within the PyMOL framework can hugely simplify these tasks. Sequence similarity searches, multiple sequence and structural alignments generation and editing, and even the possibility to merge sequence and structure alignments have been implemented in PyMod, with the aim of creating a simple, yet powerful tool for sequence and structure analysis and building of homology models. Conclusions PyMod represents a new tool for the analysis and the manipulation of protein sequences and structures. The ease of use, integration with many sequence retrieving and alignment tools and PyMOL, one of the most used molecular visualization system, are the key features of this tool. Source code, installation instructions, video tutorials and a user's guide are freely available at the URL http://schubert.bio.uniroma1.it/pymod/index.html PMID:22536966

  19. Seismic evidence of conjugate normal faulting: The 1994 Devil Canyon earthquake sequence near Challis, Idaho

    SciTech Connect

    Jackson, Suzette M.

    1994-08-01

    Aftershock hypocenters of the 1984 Devil Canyon, Idaho earthquake indicate the sequence was associated with conjugate normal faulting on two northwest-striking normal faults that bound the Warm Spring Creek graben.

  20. Advanced accident sequence precursor analysis level 1 models

    SciTech Connect

    Sattison, M.B.; Thatcher, T.A.; Knudsen, J.K.; Schroeder, J.A.; Siu, N.O.

    1996-03-01

    INEL has been involved in the development of plant-specific Accident Sequence Precursor (ASP) models for the past two years. These models were developed for use with the SAPHIRE suite of PRA computer codes. They contained event tree/linked fault tree Level 1 risk models for the following initiating events: general transient, loss-of-offsite-power, steam generator tube rupture, small loss-of-coolant-accident, and anticipated transient without scram. Early in 1995 the ASP models were revised based on review comments from the NRC and an independent peer review. These models were released as Revision 1. The Office of Nuclear Regulatory Research has sponsored several projects at the INEL this fiscal year to further enhance the capabilities of the ASP models. Revision 2 models incorporates more detailed plant information into the models concerning plant response to station blackout conditions, information on battery life, and other unique features gleaned from an Office of Nuclear Reactor Regulation quick review of the Individual Plant Examination submittals. These models are currently being delivered to the NRC as they are completed. A related project is a feasibility study and model development of low power/shutdown (LP/SD) and external event extensions to the ASP models. This project will establish criteria for selection of LP/SD and external initiator operational events for analysis within the ASP program. Prototype models for each pertinent initiating event (loss of shutdown cooling, loss of inventory control, fire, flood, seismic, etc.) will be developed. A third project concerns development of enhancements to SAPHIRE. In relation to the ASP program, a new SAPHIRE module, GEM, was developed as a specific user interface for performing ASP evaluations. This module greatly simplifies the analysis process for determining the conditional core damage probability for a given combination of initiating events and equipment failures or degradations.

  1. Universal power law behaviors in genomic sequences and evolutionary models

    NASA Astrophysics Data System (ADS)

    Martignetti, Loredana; Caselle, Michele

    2007-08-01

    We study the length distribution of a particular class of DNA sequences known as the 5' untranslated regions exons. These exons belong to the messenger RNA of protein coding genes, but they are not coding (they are located upstream of the coding portion of the mRNA) and are thus less constrained from an evolutionary point of view. We show that in both mice and humans these exons show a very clean power law decay in their length distribution and suggest a simple evolutionary model, which may explain this finding. We conjecture that this power law behavior could indeed be a general feature of higher eukaryotes.

  2. Modeling a bus through a sequence of traffic lights.

    PubMed

    Villalobos, Jorge; Muñoz, Víctor; Rogan, José; Zarama, Roberto; Penagos, Juan Felipe; Toledo, Benjamín; Valdivia, Juan Alejandro

    2015-07-01

    We propose a model of a bus traveling through a sequence of traffic lights, which is required to stop between the traffic signals to pick up passengers. A two dimensional model, of velocity and traveled time at each traffic light, is constructed, which shows non-trivial and chaotic behaviors for realistic city traffic parameters. We restrict the parameter values where these non-trivial and chaotic behaviors occur, by following analytically and numerically the fixed points and period 2 orbits. We define conditions where chaos may arise by determining regions in parameter space where the maximum Lyapunov exponent is positive. Chaos seems to occur as long as the ratio of the braking and accelerating capacities are greater than about ∼3.

  3. Largest Aftershocks of Megathrust Earthquakes in the World

    NASA Astrophysics Data System (ADS)

    Koyama, J.; Tsuzuki, M.

    2012-12-01

    The 2011 Tohoku-oki megathrust earthquake of Mw9.0 induced the earthquake activity in high level all over Japan. It included not only earthquakes near active faults but also volcanic earthquakes. Although we have observed tens of thousands of aftershocks, yet we do not know which is the largest aftershock of the 2011 megathrust. There occurred several megathrust earthquakes worldwide in the last one hundred years, which are almost the same size or larger than the 2011 megathrust. We have studied their largest aftershocks based on our new hypothesis of along-dip double segmentation (ADDS) and along-strike single segmentation (ASSS). ADDS in the Tohoku-oki region along the Japan trench is characterized by the apparent absence of earthquakes in the trench-ward segments as opposed to the Japan Island-ward segments that have repeated small earthquakes of up to Mw8 class. In contrast, the 1960 Chile and the 2010 Maule megathrusts are characterized by ASSS with the weak seismic activity before the main event everywhere in the subduction zone. The difference between these two types of seismic segmentations would be that strongly coupled areas of trench-ward segments give rise to ADDS, whereas almost 100% coupled areas of shallow-parts of subduction zones give rise to ASSS. In other words, the phenomenon of a seismic gap can be identified for an ASSS megathrust, where as a doughnut pattern of seismic activity appears prior to a main ADDS event. In summary, most of the largest aftershocks of ADDS megathrusts are earthquakes of outer-rise(outer trench-slope) normal faultings, where there occur two types, dip-slip and strike-slip, depending on the structure of subducting oceanic plates. The 1933 Sanriku-oki Mw8.6 (the 1896 Meiji-Sanriku M~8.5) and the 2011 Tohoku-oki Mw7.7 (the 2011 Tohoku-oki Mw9.0) are the former and the 1987 Off Alaska Mw7.8 (the 1964 Alaska Mw9.2) and the 2012 Sumatra Mw8.6 (the 2004 Sumatra-Andaman Mw9.3) are the latter. Those of ASSS megathrusts occurred

  4. Universal Sequence Replication, Reversible Polymerization and Early Functional Biopolymers: A Model for the Initiation of Prebiotic Sequence Evolution

    PubMed Central

    Walker, Sara Imari; Grover, Martha A.; Hud, Nicholas V.

    2012-01-01

    Many models for the origin of life have focused on understanding how evolution can drive the refinement of a preexisting enzyme, such as the evolution of efficient replicase activity. Here we present a model for what was, arguably, an even earlier stage of chemical evolution, when polymer sequence diversity was generated and sustained before, and during, the onset of functional selection. The model includes regular environmental cycles (e.g. hydration-dehydration cycles) that drive polymers between times of replication and functional activity, which coincide with times of different monomer and polymer diffusivity. Template-directed replication of informational polymers, which takes place during the dehydration stage of each cycle, is considered to be sequence-independent. New sequences are generated by spontaneous polymer formation, and all sequences compete for a finite monomer resource that is recycled via reversible polymerization. Kinetic Monte Carlo simulations demonstrate that this proposed prebiotic scenario provides a robust mechanism for the exploration of sequence space. Introduction of a polymer sequence with monomer synthetase activity illustrates that functional sequences can become established in a preexisting pool of otherwise non-functional sequences. Functional selection does not dominate system dynamics and sequence diversity remains high, permitting the emergence and spread of more than one functional sequence. It is also observed that polymers spontaneously form clusters in simulations where polymers diffuse more slowly than monomers, a feature that is reminiscent of a previous proposal that the earliest stages of life could have been defined by the collective evolution of a system-wide cooperation of polymer aggregates. Overall, the results presented demonstrate the merits of considering plausible prebiotic polymer chemistries and environments that would have allowed for the rapid turnover of monomer resources and for regularly varying monomer

  5. CAPRG: sequence assembling pipeline for next generation sequencing of non-model organisms.

    PubMed

    Rawat, Arun; Elasri, Mohamed O; Gust, Kurt A; George, Glover; Pham, Don; Scanlan, Leona D; Vulpe, Chris; Perkins, Edward J

    2012-01-01

    Our goal is to introduce and describe the utility of a new pipeline "Contigs Assembly Pipeline using Reference Genome" (CAPRG), which has been developed to assemble "long sequence reads" for non-model organisms by leveraging a reference genome of a closely related phylogenetic relative. To facilitate this effort, we utilized two avian transcriptomic datasets generated using ROCHE/454 technology as test cases for CAPRG assembly. We compared the results of CAPRG assembly using a reference genome with the results of existing methods that utilize de novo strategies such as VELVET, PAVE, and MIRA by employing parameter space comparisons (intra-assembling comparison). CAPRG performed as well or better than the existing assembly methods based on various benchmarks for "gene-hunting." Further, CAPRG completed the assemblies in a fraction of the time required by the existing assembly algorithms. Additional advantages of CAPRG included reduced contig inflation resulting in lower computational resources for annotation, and functional identification for contigs that may be categorized as "unknowns" by de novo methods. In addition to providing evaluation of CAPRG performance, we observed that the different assembly (inter-assembly) results could be integrated to enhance the putative gene coverage for any transcriptomics study.

  6. Collagen model peptides: Sequence dependence of triple-helix stability.

    PubMed

    Persikov, A V; Ramshaw, J A; Brodsky, B

    2000-01-01

    The triple helix is a specialized protein motif, found in all collagens as well as in noncollagenous proteins involved in host defense. Peptides will adopt a triple-helical conformation if the sequence contains its characteristic features of Gly as every third residue and a high content of Pro and Hyp residues. Such model peptides have proved amenable to structural studies by x-ray crystallography and NMR spectroscopy, suitable for thermodynamic and kinetic analysis, and a valuable tool in characterizing the binding activities of the collagen triple helix. A systematic approach to understanding the amino acid sequence dependence of the collagen triple helix has been initiated, based on a set of host-guest peptides of the form, (Gly-Pro-Hyp)(3)-Gly-X-Y-(Gly-Pro-Hyp)(4). Comparison of their thermal stabilities has led to a propensity scale for the X and Y positions, and the additivity of contributions of individual residues is now under investigation. The local and global stability of the collagen triple helix is normally modulated by the residues in the X and Y positions, with every third position occupied by Gly in fibril-forming collagens. However, in collagen diseases, such as osteogenesis imperfecta, a single Gly may be substituted by another residue. Host-guest studies where the Gly is replaced by various amino acids suggest that the identity of the residue in the Gly position affects the degree of destabilization and the clinical severity of the disease.

  7. Tectonic geomorphology, aftershock relocation, and sources of the great 1950 and 1897 East Himalayan earthquakes

    NASA Astrophysics Data System (ADS)

    Kali, E.; Choudhury, S.; Tapponnier, P.; van der Woerd, J.; Okal, E. A.; Bollinger, L.; Banerjee, P.; Baruah, S.; Coudurier-Curveur, A.

    2013-12-01

    The exact sources and mechanisms of the great Assam (1950) and Shillong (1897) earthquakes, largest instrumental events to date along the Himalayan range (with maximum magnitudes of 8.5, and 8.7, respectively), have remained unclear. Here we use high-resolution Digital Elevation Models (DEM) derived from Cartosat and Pleiades satellite scenes, in conjunction with geomorphic fieldwork and a relocation of instrumentally recorded aftershocks, to untangle the long-standing controversies surrounding these Northeastern Indian earthquakes. The DEMs help map long, steep, regionally unique, 3 to 30 m-high tectonic escarpments cutting across fluvial terraces, risers and valleys, that unquestionably mark the primary surface ruptures of very large events. The scarps follow the base of the cusped range-front of the Arunachal Pradesh Himalayas, and of the sharply flexed southern edge of the northward-tilted Shillong plateau, respectively between ≈ 94° (≈ Subansiri River) and 97°E (≈ Vijaynagar), and 90°10' (Tura) and 92°15'E (Shari River). The corresponding sources, primarily on shallow north-dipping thrusts, are the only ones that can account comprehensively for the large moments of the two earthquakes, their aftershock distributions, and the aerial extent of observed landslides, as well as for most instrumental records and other historical observations. For the Assam earthquake, two nearly orthogonal faults meeting at the cusp of the Arunachal Pradesh syntaxis were involved. The faults - Abor Hills Thrust or eastern MFT, and Mishmi Hills Thrust - may have shared a common co-seismic slip vector, roughly parallel to their intersection. This would imply a dominant right-lateral strike-slip component on the Mishmi Thrust, which merges southwards with the main branch of the Sagaing Fault, and reconcile the two distinct focal mechanisms obtained by previous authors.

  8. Human Inferences about Sequences: A Minimal Transition Probability Model

    PubMed Central

    2016-01-01

    The brain constantly infers the causes of the inputs it receives and uses these inferences to generate statistical expectations about future observations. Experimental evidence for these expectations and their violations include explicit reports, sequential effects on reaction times, and mismatch or surprise signals recorded in electrophysiology and functional MRI. Here, we explore the hypothesis that the brain acts as a near-optimal inference device that constantly attempts to infer the time-varying matrix of transition probabilities between the stimuli it receives, even when those stimuli are in fact fully unpredictable. This parsimonious Bayesian model, with a single free parameter, accounts for a broad range of findings on surprise signals, sequential effects and the perception of randomness. Notably, it explains the pervasive asymmetry between repetitions and alternations encountered in those studies. Our analysis suggests that a neural machinery for inferring transition probabilities lies at the core of human sequence knowledge. PMID:28030543

  9. Sequence determination from overlapping fragments: a simple model of whole-genome shotgun sequencing.

    PubMed

    Derrida, Bernard; Fink, Thomas M A

    2002-02-11

    Assembling fragments randomly sampled from along a sequence is the basis of whole-genome shotgun sequencing, a technique used to map the DNA of the human and other genomes. We calculate the probability that a random sequence can be recovered from a collection of overlapping fragments. We provide an exact solution for an infinite alphabet and in the case of constant overlaps. For the general problem we apply two assembly strategies and give the probability that the assembly puzzle can be solved in the limit of infinitely many fragments.

  10. Sequence Determination from Overlapping Fragments: A Simple Model of Whole-Genome Shotgun Sequencing

    NASA Astrophysics Data System (ADS)

    Derrida, Bernard; Fink, Thomas M.

    2002-02-01

    Assembling fragments randomly sampled from along a sequence is the basis of whole-genome shotgun sequencing, a technique used to map the DNA of the human and other genomes. We calculate the probability that a random sequence can be recovered from a collection of overlapping fragments. We provide an exact solution for an infinite alphabet and in the case of constant overlaps. For the general problem we apply two assembly strategies and give the probability that the assembly puzzle can be solved in the limit of infinitely many fragments.

  11. Image sequence coding using 3D scene models

    NASA Astrophysics Data System (ADS)

    Girod, Bernd

    1994-09-01

    The implicit and explicit use of 3D models for image sequence coding is discussed. For implicit use, a 3D model can be incorporated into motion compensating prediction. A scheme that estimates the displacement vector field with a rigid body motion constraint by recovering epipolar lines from an unconstrained displacement estimate and then repeating block matching along the epipolar line is proposed. Experimental results show that an improved displacement vector field can be obtained with a rigid body motion constraint. As an example for explicit use, various results with a facial animation model for videotelephony are discussed. A 13 X 16 B-spline mask can be adapted automatically to individual faces and is used to generate facial expressions based on FACS. A depth-from-defocus range camera suitable for real-time facial motion tracking is described. Finally, the real-time facial animation system `Traugott' is presented that has been used to generate several hours of broadcast video. Experiments suggest that a videophone system based on facial animation might require a transmission bitrate of 1 kbit/s or below.

  12. Detecting Hidden Aftershocks of the 2015 Mw 7.8 Gorkha Earthquake Using Multiple Global Seismic Arrays

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; LI, B.

    2015-12-01

    Spatio-temporal evolution of aftershocks is important for the study of rupture extent [McCann et al., 1979], stress transfer [King et al., 1994], postseismic deformation [Hsu et al., 2006; Sladen et al., 2010], hazard assessment and forecasting of future seismicity [e.g., Cocco et al., 2010]. However, many aftershocks remain undetected by the global network due to the limitation of the density and distribution of seismic instruments. In this study, we use the back-projection method with multiple global seismic arrays to detect the hidden earthquakes (not recorded by current standard global earthquake catalog) following the 2015 Mw 7.8 Gorkha earthquake. There are 140 aftershocks in the global catalog within 10 days since the mainshock. Using array methods, we are able to detect about twice as many events near the mainshock. According to the Advanced National Seismic System (ANSS) comprehensive earthquake catalog, the first aftershock happened 4 minutes after the mainshock. We detect aftershocks even before that event. This shows that back-projection can be used to detect early aftershocks in global scale, which usually remain undetected by the arrival of various seismic phases immediately following a large earthquake [Lengline et al., 2012]. Detection of these hidden aftershocks provides a more complete picture of the spatiotemporal distribution of aftershock activity and helps improve the completeness of the global standard aftershock catalog. Our improved aftershock catalog shows east-west aftershocks distribution (Figure 1), similar to the ANSS catalog. In addition, we detect significant number of aftershocks north, south, and within the coseismic rupture area. The improved aftershock catalog using existing global seismic arrays enables us to better study aftershocks dynamics, stress evolution and earthquake characteristics.

  13. Depth of faulting during the 1968 Meckering, Australia, Earthquake sequence determined from waveform analysis of local seismograms

    NASA Astrophysics Data System (ADS)

    Langston, Charles A.

    1987-10-01

    Waveforms for 11 foreshocks and 48 aftershocks of the Ms 6.8 Meckering earthquake recorded at the World-Wide Standard Seismograph Network station Mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence. Clear depth phases including sP and Rg are seen in the local Seismograms at distances of 60-95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques. Large Rg/S ratios seen on the vertical component short-period data for many events imply source depths less than 2 km. The short-period P waveform contains the best depth estimator in the form of sP so that depth can be estimated to within an uncertainty of about 1 km for most events. The foreshocks cluster at less than 2 km depth, and most aftershocks occur within 1 km of the surface. A few aftershocks occur as deep as 7 km. These results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1.5 km depth with rupture proceeding downward and not exceeding 6 km depth. These results, coupled with previous stress studies in the Australian shield and models of crustal strength, show that faulting in a cold shield area is a near-surface phenomenon and implies that most of the crust is too strong to be fractured.

  14. Financial earthquakes, aftershocks and scaling in emerging stock markets

    NASA Astrophysics Data System (ADS)

    Selçuk, Faruk

    2004-02-01

    This paper provides evidence for scaling laws in emerging stock markets. Estimated parameters using different definitions of volatility show that the empirical scaling law in every stock market is a power law. This power law holds from 2 to 240 business days (almost 1 year). The scaling parameter in these economies changes after a change in the definition of volatility. This finding indicates that the stock returns may have a multifractal nature. Another scaling property of stock returns is examined by relating the time after a main shock to the number of aftershocks per unit time. The empirical findings show that after a major fall in the stock returns, the stock market volatility above a certain threshold shows a power law decay, described by Omori's law.

  15. Estimating ETAS: the effects of truncation, missing data, and model assumptions

    NASA Astrophysics Data System (ADS)

    Seif, Stefanie; Mignan, Arnaud; Zechar, Jeremy; Werner, Maximilian; Wiemer, Stefan

    2016-04-01

    The Epidemic-Type Aftershock Sequence (ETAS) model is widely used to describe the occurrence of earthquakes in space and time, but there has been little discussion of the limits of, and influences on, its estimation. What has been established is that ETAS parameter estimates are influenced by missing data (e.g., earthquakes are not reliably detected during lively aftershock sequences) and by simplifying assumptions (e.g., that aftershocks are isotropically distributed). In this article, we investigate the effect of truncation: how do parameter estimates depend on the cut-off magnitude, Mcut, above which parameters are estimated? We analyze catalogs from southern California and Italy and find that parameter variations as a function of Mcut are caused by (i) changing sample size (which affects e.g. Omori's cconstant) or (ii) an intrinsic dependence on Mcut (as Mcut increases, absolute productivity and background rate decrease). We also explore the influence of another form of truncation - the finite catalog length - that can bias estimators of the branching ratio. Being also a function of Omori's p-value, the true branching ratio is underestimated by 45% to 5% for 1.05< p <1.2. Finite sample size affects the variation of the branching ratio estimates. Moreover, we investigate the effect of missing aftershocks and find that the ETAS productivity parameters (α and K0) and the Omoris c-value are significantly changed only for low Mcut=2.5. We further find that conventional estimation errors for these parameters, inferred from simulations that do not account for aftershock incompleteness, are underestimated by, on average, a factor of six.

  16. The tectonic context of the destructive 2010-2011 Canterbury, New Zealand, earthquake sequence

    NASA Astrophysics Data System (ADS)

    Reyners, M.; Eberhart-Phillips, D. M.; Bannister, S. C.; Martin, S.

    2011-12-01

    The destructive Canterbury, New Zealand, earthquake sequence has resulted in 181 deaths and caused damage in the US$15 billion range. A dense network of accelerographs has recorded an exceptional set of strong ground motions, with peak ground accelerations reaching 1.26 g during the Mw 7.1 mainshock on 04 September 2010, 2.20 g during the Mw 6.2 aftershock on 22 February 2011, and 2.04 g during the Mw 6.0 aftershock on 13 June 2011. This ongoing sequence raises important questions about the hazard from infrequent intraplate earthquakes in low strain rate regions (a few mm/yr in the case of the Canterbury region), including: 1) Why was the shaking from these events so strong? 2) Why does this earthquake sequence continue to be so productive? 3) Would we expect a similar earthquake sequence in other low-strain regions? Here we investigate these questions by carrying out a fine scale 3-D tomographic inversion for crustal structure using arrival time data from aftershocks, regional seismicity and active source data. We carry out a series of gradational inversions, using the recently determined New Zealand nationwide 3-D seismic velocity model as our initial model. Our 3-D model shows that structural features shallow around the northern edge of Banks Peninsula, a basaltic shield volcano immediately south of the city of Christchurch that was active during the period 12 - 6 Myr ago. Our results suggest that crustal structure has played a first order role in the earthquake sequence. At approximately 10 km depth, we have a ca. 100 Myr-old plate boundary, marking the subduction thrust where the Hikurangi Plateau (a large igneous province) subducted under the edge of Gondwana. This plateau is extremely strong and has a very deep brittle-ductile transition - small earthquakes extend down to 35 km depth in the mafic plateau. The larger earthquakes in the sequence occurred within the greywacke and schist capping this strong plateau. The high stress drops and strong shaking from

  17. Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

    USGS Publications Warehouse

    Neighbors, Corrie; Liao, E. J.; Cochran, Elizabeth S.; Funning, G. J.; Chung, A. I.; Lawrence, J. F.; Christensen, C. M.; Miller, M.; Belmonte, A.; Sepulveda, H. H. Andrés

    2014-01-01

    The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 Mw 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (ML ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ0, and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κobservations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site

  18. Investigation of the high-frequency attenuation parameter, κ (kappa), from aftershocks of the 2010 Mw 8.8 Maule, Chile earthquake

    NASA Astrophysics Data System (ADS)

    Neighbors, C.; Liao, E. J.; Cochran, E. S.; Funning, G. J.; Chung, A. I.; Lawrence, J. F.; Christensen, C.; Miller, M.; Belmonte, A.; Andrés Sepulveda, H. H.

    2015-01-01

    The Bío Bío region of Chile experienced a vigorous aftershock sequence following the 2010 February 27 Mw 8.8 Maule earthquake. The immediate aftershock sequence was captured by two temporary seismic deployments: the Quake Catcher Network Rapid Aftershock Mobilization Program (QCN RAMP) and the Incorporated Research Institutions for Seismology CHile Aftershock Mobilization Program (IRIS CHAMP). Here, we use moderate to large aftershocks (ML ≥ 4.0) occurring between 2010 March 1 and June 30 recorded by QCN RAMP and IRIS CHAMP stations to determine the spectral decay parameter, kappa (κ). First, we compare waveforms and κ estimates from the lower-resolution QCN stations to the IRIS CHAMP stations to ensure the QCN data are of sufficient quality. We find that QCN stations provide reasonable estimates of κ in comparison to traditional seismic sensors and provide valuable additional observations of local ground motion variation. Using data from both deployments, we investigate the variation in κ for the region to determine if κ is influenced primarily by local geological structure, path attenuation, or source properties (e.g. magnitude, mechanism and depth). Estimates of κ for the Bío Bío region range from 0.0022 to 0.0704 s with a mean of 0.0295 s and are in good agreement with κ values previously reported for similar tectonic environments. κ correlates with epicentral distance and, to a lesser degree, with source magnitude. We find little to no correlation between the site kappa, κ0, and mapped geology, although we were only able to compare the data to a low-resolution map of surficial geology. These results support an increasing number of studies that suggest κ observations can be attributed to a combination of source, path and site properties; additionally, measured κ are often highly scattered making it difficult to separate the contribution from each of these factors. Thus, our results suggest that contributions from the site, path and source

  19. Quantifying Aluminum Crystal Size Part 2: The Model-Development Sequence

    ERIC Educational Resources Information Center

    Hjalmarson, Margret; Diefes-Dux, Heidi A.; Bowman, Keith; Zawojewski, Judith S.

    2006-01-01

    We have designed model-development sequences using a common context to provide authentic problem-solving experiences for first-year students. The model-development sequence takes a model-eliciting activity a step further by engaging students in the exploration and adaptation of a mathematical model (e.g., procedure, algorithm, method) for solving…

  20. Detailed fault structure of the 2000 Western Tottori, Japan, earthquake sequence

    USGS Publications Warehouse

    Fukuyama, E.; Ellsworth, W.L.; Waldhauser, F.; Kubo, A.

    2003-01-01

    We investigate the faulting process of the aftershock region of the 2000 western Tottori earthquake (Mw 6.6) by combining aftershock hypocenters and moment tensor solutions. Aftershock locations were precisely determined by the double difference method using P- and S-phase arrival data of the Japan Meteorological Agency unified catalog. By combining the relocated hypocenters and moment tensor solutions of aftershocks by broadband waveform inversion of FREESIA (F-net), we successfully resolved very detailed fault structures activated by the mainshock. The estimated fault model resolves 15 individual fault segments that are consistent with both aftershock distribution and focal mechanism solutions. Rupture in the mainshock was principally confined to the three fault elements in the southern half of the zone, which is also where the earliest aftershocks concentrate. With time, the northern part of the zone becomes activated, which is also reflected in the postseismic deformation field. From the stress tensor analysis of aftershock focal mechanisms, we found a rather uniform stress field in the aftershock region, although fault strikes were scattered. The maximum stress direction is N107??E, which is consistent with the tectonic stress field in this region. In the northern part of the fault, where no slip occurred during the mainshock but postseismic slip was observed, the maximum stress direction of N130??E was possible as an alternative solution of stress tensor inversion.

  1. Cataloging the 1811-1812 New Madrid, central U.S., earthquake sequence

    USGS Publications Warehouse

    Hough, S.E.

    2009-01-01

    The three principal New Madrid, central U.S., mainshocks of 1811-1812 were followed by extensive aftershock sequences that included numerous felt events. Although no instrumental data are available for the sequence, historical accounts provide information that can be used to estimate magnitudes and locations for the large aftershocks as well as the mainshocks. Several detailed eyewitness accounts of the sequence provide sufficient information to identify times and rough magnitude estimates for a number of aftershocks that have not been analyzed previously. I also use three extended compilations of felt events to explore the overall sequence productivity. Although one generally cannot estimate magnitudes or locations for individual events, the intensity distributions of recent, instrumentally recorded earthquakes in the region provide a basis for estimation of the magnitude distribution of 1811-1812 aftershocks. The distribution is consistent with a b-value distribution. I estimate Mw 6-6.3 for the three largest identifiable aftershocks, apart from the so-called dawn aftershock on 16 December 1811.

  2. The 2012 Sumatra great earthquake sequence

    NASA Astrophysics Data System (ADS)

    Duputel, Zacharie; Kanamori, Hiroo; Tsai, Victor C.; Rivera, Luis; Meng, Lingsen; Ampuero, Jean-Paul; Stock, Joann M.

    2012-10-01

    The equatorial Indian Ocean is a well known place of active intraplate deformation defying the conventional view of rigid plates separated by narrow boundaries where deformation is confined. On 11 April 2012, this region was hit in a couple of hours by two of the largest strike-slip earthquakes ever recorded (moment magnitudes Mw=8.6 and 8.2). Broadband seismological observations of the Mw=8.6 mainshock indicate a large centroid depth (˜30 km) and remarkable rupture complexity. Detailed study of the surface-wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents. To account for these observations, we developed a procedure to invert for multiple-point-source parameters. The optimum source model at long period consists of two point sources separated by about 209 km with magnitudes Mw=8.5 and 8.3. To explain the remaining discrepancies between predicted and observed surface waves, we can refine this model by adding directivity along the WNW-ESE axis. However, we do not exclude more complicated models. To analyze the Mw=8.2 aftershock, we removed the perturbation due to large surface-wave arrivals of the Mw=8.6 mainshock by subtracting the corresponding synthetics computed for the two-subevent model. Analysis of the surface-wave amplitudes suggests that the Mw=8.2 aftershock had a large centroid depth between 30 km and 40 km. This major earthquake sequence brings a new perspective to the seismotectonics of the equatorial Indian Ocean and reveals active deep lithospheric deformation.

  3. The 2015 April 25 Gorkha (Nepal) Earthquake and its Aftershocks: Implications for lateral heterogeneity on the Main Himalayan Thrust

    NASA Astrophysics Data System (ADS)

    Kumar, Ajay; Singh, Shashwat K.; Mitra, S.; Priestley, K. F.; Dayal, Shankar

    2016-11-01

    The 2015 Gorkha earthquake (Mw 7.8) occurred by thrust faulting on a ˜150 km long and ˜70 km wide, locked downdip segment of the Main Himalayan Thrust (MHT), causing the Himalaya to slip SSW over the Indian Plate, and was followed by major-to-moderate aftershocks. Back projection of teleseismic P-wave and inversion of teleseismic body waves provide constraints on the geometry and kinematics of the mainshock rupture and source mechanism of aftershocks. The mainshock initiated ˜80 km west of Katmandu, close to the locking line on the MHT and propagated eastwards along ˜117° azimuth for a duration of ˜70 s, with varying rupture velocity on a heterogeneous fault surface. The mainshock has been modeled using four sub-events, propagating from west-to-east. The first sub-event (0-20 s) ruptured at a velocity of ˜3.5 km s^{-1} on a ˜6° N dipping flat segment of the MHT with thrust motion. The second sub-event (20-35 s) ruptured a ˜18° W dipping lateral ramp on the MHT in oblique thrust motion. The rupture velocity dropped from 3.5 km s^{-1} to 2.5 km s^{-1}, as a result of updip propagation of the rupture. The third sub-event (35-50 s) ruptured a ˜7° N dipping, eastward flat segment of the MHT with thrust motion and resulted in the largest amplitude arrivals at teleseismic distances. The fourth sub-event (50-70 s) occurred by left-lateral strike-slip motion on a steeply dipping transverse fault, at high angle to the MHT and arrested the eastward propagation of the mainshock rupture. Eastward stress build-up following the mainshock resulted in the largest aftershock (Mw 7.3), which occurred on the MHT, immediately east of the mainshock rupture. Source mechanisms of moderate aftershocks reveal stress adjustment at the edges of the mainshock fault, flexural faulting on top of the downgoing Indian Plate and extensional faulting in the hanging wall of the MHT.

  4. The 2015 April 25 Gorkha (Nepal) earthquake and its aftershocks: implications for lateral heterogeneity on the Main Himalayan Thrust

    NASA Astrophysics Data System (ADS)

    Kumar, Ajay; Singh, Shashwat K.; Mitra, S.; Priestley, K. F.; Dayal, Shankar

    2017-02-01

    The 2015 Gorkha earthquake (Mw 7.8) occurred by thrust faulting on a ˜150 km long and ˜70 km wide, locked downdip segment of the Main Himalayan Thrust (MHT), causing the Himalaya to slip SSW over the Indian Plate, and was followed by major-to-moderate aftershocks. Back projection of teleseismic P-wave and inversion of teleseismic body waves provide constraints on the geometry and kinematics of the main-shock rupture and source mechanism of aftershocks. The main-shock initiated ˜80 km west of Katmandu, close to the locking line on the MHT and propagated eastwards along ˜117° azimuth for a duration of ˜70 s, with varying rupture velocity on a heterogeneous fault surface. The main-shock has been modelled using four subevents, propagating from west-to-east. The first subevent (0-20 s) ruptured at a velocity of ˜3.5 km s- 1 on a ˜6°N dipping flat segment of the MHT with thrust motion. The second subevent (20-35 s) ruptured a ˜18° W dipping lateral ramp on the MHT in oblique thrust motion. The rupture velocity dropped from 3.5 km s- 1 to 2.5 km s- 1, as a result of updip propagation of the rupture. The third subevent (35-50 s) ruptured a ˜7°N dipping, eastward flat segment of the MHT with thrust motion and resulted in the largest amplitude arrivals at teleseismic distances. The fourth subevent (50-70 s) occurred by left-lateral strike-slip motion on a steeply dipping transverse fault, at high angle to the MHT and arrested the eastward propagation of the main-shock rupture. Eastward stress build-up following the main-shock resulted in the largest aftershock (Mw 7.3), which occurred on the MHT, immediately east of the main-shock rupture. Source mechanisms of moderate aftershocks reveal stress adjustment at the edges of the main-shock fault, flexural faulting on top of the downgoing Indian Plate and extensional faulting in the hanging wall of the MHT.

  5. Insights from the 2011 Prague, Oklahoma earthquake sequence on the role of damage zones in the seismic cycle

    NASA Astrophysics Data System (ADS)

    Savage, H. M.; Dieck, C. C.; Keranen, K. M.

    2013-12-01

    Although most faults are surrounded by a halo of fractured rock known as a damage zone, it is not clear what role damage zones play during the seismic cycle on mature faults. Here, we present a superbly-located foreshock-mainshock-aftershock sequence that demonstrates most aftershocks are located within the damage zone surrounding the fault. The 2011 Prague, Oklahoma sequence included three M5+ earthquakes along three different faults over a three-day period. The third event was captured with an array of nine seismometers with ~2 km spacing, allowing for precise event location. We located more than 1000 foreshocks and aftershocks of the November 8 M5 event within a 14 hour time window, and relocated these aftershocks using singular-value decomposition in HypoDD. Because of the accuracy in event horizontal location, we can use these events to compare aftershock distribution to fracture distributions within damage zones surrounding faults. The aftershock sequence localizes to a damage zone thickness that scales with the length of the rupture patch, similar to previously documented scaling between fault length and damage zone thickness. Furthermore, the falloff in aftershock density decays precipitously away from the fault, in a similar fashion to fracture density decay in damage zones. Most aftershocks in this sequence occur within the first hour after the mainshock, and there is no obvious migration of aftershocks away from the fault with time. Finally, foreshock activity along this fault was limited to the intersection with the fault that had hosted a M5.7 earthquake two days prior.

  6. Sensitivity study of forecasted aftershock seismicity based on Coulomb stress calculation and rate- and state-dependent frictional response (Invited)

    NASA Astrophysics Data System (ADS)

    Cocco, M.; Hainzl, S.; Woessner, J.; Enescu, B.; Catalli, F.; Lombardi, A.

    2009-12-01

    It is nowadays well established that both Coulomb stress perturbations and the rate- and state-dependent frictional response of fault populations are needed to model the spatial and temporal evolution of seismicity. This represents the most popular physics-based approach to forecast the rate of earthquake production and its performances have to be verified with respect to alternative statistical methods. Despite the numerous applications of Coulomb stress interactions, a rigorous validation of the forecasting capabilities is still missing. In this work, we use the Dieterich (1994) physics-based approach to simulate the spatio-temporal evolution of seismicity caused by stress changes applied to an infinite population of nucleating patches modelled through a rate- and state-dependent friction law. According to this model, seismicity rate changes depend on the amplitude of stress perturbation, the physical constitutive properties of faults (represented by the parameter Aσ), the stressing rate and the background seismicity rate of the study area. In order to apply this model in a predictive manner, we need to understand the variability of input physical model parameters and their correlations. We first discuss the impact of uncertainties in model parameters and, in particular, in computed coseismic stress perturbations on the seismicity rate changes forecasted through the frictional model. We aim to understand how the variability of Coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production. We use the aftershock activity following the 1992 M 7.3 Landers (California) earthquake as one of our case studies. We analyze the variability of stress changes resulting from the use of different published slip distributions. We find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio, the coefficient of variation (CV), is approximately constant in

  7. Investigations of Periodic Disturbances on Seismic Aftershock Recordings

    NASA Astrophysics Data System (ADS)

    Liebsch, Mattes; Gorschlüter, Felix; Knoop, Jan-Frederik; Altmann, Jürgen

    2013-04-01

    The Comprehensive Nuclear Test-Ban Treaty Organisation (CTBTO) runs the International Monitoring System (IMS) to detect possible violations of the treaty. The seismic sensors of the IMS are set up to detect every underground explosion with a yield of 1 kT TNT equivalent or even better everywhere on the world. Under consideration of all IMS data the hypocentre of a large underground explosion is located within an area of about 1000 sq km. To verify if it was a violation of the Test-Ban Treaty the CTBTO (after CTBT entry into force) is allowed to carry out an on-site inspection (OSI) in the area of suspicion. During an OSI the hypocentre is to be located much more precisely; for this a local seismic aftershock monitoring system (SAMS) can be installed to detect small seismic events caused as a consequence of the explosion, such as relaxation of the rock around the cavity. However the magnitude of these aftershock signals is extremely weak. Other difficulties arise from other seismic signals in the inspection area, for example caused by vehicles of the inspectors, from coupling of airborne signals to the ground, or even by intended attempts to disturb the OSI. While the aftershock signals have a pulsed shape, man-made seismic signals (primarily created by engines) usually show periodic characteristics and thus are representable as a sum of sine functions and their harmonics. A mathematical expression for the Hann-windowed discrete Fourier transform of the underlying sine is used to characterise every such disturbance by the amplitude, frequency and phase. The contributions of these sines are computed and subtracted from the complex spectrum sequentially. Synthetic sines superposed to real signals, orders of magnitude stronger than the latter, can be removed successfully. Removal of periodic content from the signals of a helicopter overflight reduces the amplitude by a factor 3.3 when the frequencies are approximately constant. To reduce or prevent disturbing seismic

  8. Reference genome sequence of the model plant Setaria

    SciTech Connect

    Bennetzen, Jeffrey L; Yang, Xiaohan; Ye, Chuyu; Tuskan, Gerald A

    2012-01-01

    We generated a high-quality reference genome sequence for foxtail millet (Setaria italica). The {approx}400-Mb assembly covers {approx}80% of the genome and >95% of the gene space. The assembly was anchored to a 992-locus genetic map and was annotated by comparison with >1.3 million expressed sequence tag reads. We produced more than 580 million RNA-Seq reads to facilitate expression analyses. We also sequenced Setaria viridis, the ancestral wild relative of S. italica, and identified regions of differential single-nucleotide polymorphism density, distribution of transposable elements, small RNA content, chromosomal rearrangement and segregation distortion. The genus Setaria includes natural and cultivated species that demonstrate a wide capacity for adaptation. The genetic basis of this adaptation was investigated by comparing five sequenced grass genomes. We also used the diploid Setaria genome to evaluate the ongoing genome assembly of a related polyploid, switchgrass (Panicum virgatum).

  9. Reference genome sequence of the model plant Setaria

    SciTech Connect

    Bennetzen, Jeffrey L; Schmutz, Jeremy; Wang, Hao; Percifield, Ryan; Hawkins, Jennifer; Pontaroli, Ana C.; Estep, Matt; Feng, Liang; Vaughn, Justin N; Grimwood, Jane; Jenkins, Jerry; Barry, Kerrie; Lindquist, Erika; Hellsten, Uffe; Deshpande, Shweta; Wang, Xuewen; Wu, Xiaomei; Mitros, Therese; Triplett, Jimmy; Yang, Xiaohan; Ye, Chuyu; Mauro-Herrera, Margarita; Wang, Lin; Li, Pinghua; Sharma, Manoj; Sharma, Rita; Ronald, Pamela; Panaud, Olivier; Kellogg, Elizabeth A.; Brutnell, Thomas P.; Doust, Andrew N.; Tuskan, Gerald A; Rokhsar, Daniel; Devos, Katrien M

    2012-01-01

    We generated a high-quality reference genome sequence for foxtail millet (Setaria italica). The ~400-Mb assembly covers ~80% of the genome and >95% of the gene space. The assembly was anchored to a 992-locus genetic map and was annotated by comparison with >1.3 million expressed sequence tag reads. We produced more than 580 million RNA-Seq reads to facilitate expression analyses. We also sequenced Setaria viridis, the ancestral wild relative of S. italica, and identified regions of differential single-nucleotide polymorphism density, distribution of transposable elements, small RNA content, chromosomal rearrangement and segregation distortion. The genus Setaria includes natural and cultivated species that demonstrate a wide capacity for adaptation. The genetic basis of this adaptation was investigated by comparing five sequenced grass genomes. We also used the diploid Setaria genome to evaluate the ongoing genome assembly of a related polyploid, switchgrass (Panicum virgatum).

  10. Multi-sequence H.264/AVC Rate Control Based on the Linear Model

    NASA Astrophysics Data System (ADS)

    Pastuszak, Grzegorz; Pietrasiewicz, Andrzej

    Multi-sequence video coding can distribute bit-budget among sequences to balance the qualities subject to a common limitation on the bit-rate. This paper presents the method of selection of a common quantization parameter, which is applied concurrently to each sequence. The approach takes into account ρ-domain rate-distortion models kept independently for each video sequence and builds a common model. The output buffer is verified jointly for all the sequences and drives a joint bit allocation process. The method has been verified in simulation to demonstrate its usefulness in video encoding.

  11. Source Properties of Repeating Small Earthquakes in the Aftershock Zones of the 1999 Izmit and Duzce Earthquakes

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Y.; Peng, Z.

    2006-12-01

    We estimate the source parameters of repeating small earthquakes in the aftershock zones of the 1999 Mw7.4 Izmit and Mw7.1 Duzce earthquakes. The analysis employs 36 sets of highly repeating earthquakes, ranging in size from M 0 to M 3.0, that occurred from August 1999 to February 2000 along the Karadere-Duzce segment of the north Anatolian fault [Peng and Ben-Zion, 2006]. A local PASSCAL network consisting of 10 short-period stations recorded the data. We compute spectra from each seismogram using a multitaper technique. We measure the difference between events by dividing the spectra of the each individual record to the average spectra at that station [Vidale et al., 1994]. Stable spectra ratios are obtained by stacking the ratios calculated from moving windows starting from the P waves to the S-coda waves [Imanishi and Ellsworth, 2006]. Next, we estimate the seismic potencies and corner frequencies for events in each cluster using a simple source model. The continuing work will focus on deriving static stress drops, apparent stresses and radiated energy of these repeating earthquakes. A comparison of the source properties of the repeating small earthquakes with those of large aftershocks and the Duzce main shock would allow us to examine whether there are systematic variations with location and/or size.

  12. A preliminary study of the Santa Barbara, California, earthquake of August 13, 1978, and its major aftershocks

    USGS Publications Warehouse

    Lee, William Hung Kan; Johnson, C.E.; Henyey, T.L.; Yerkes, R.L.

    1978-01-01

    The ML5.1 Santa Barbara earthquake of August 13, 1978 occurred at lat 34 ? 22.2'N., long 119 ? 43.0' 4 km south of Santa Barbara, Calif. at a depth of 12.5 km in the northeast Santa Barbara Channel, part of the western Transverse Ranges geomorphic-structural province. This part of the province is characterized by seismically active, east-trending reverse faults and rates of coastal uplift that have averaged up to about 10 m/1000 years over the last 45,000 years. No surface rupture was detected onshore. Subsurface rupture propagated northwest from the main shock toward Goleta, 15 km west of Santa Barbara, where a maximum acceleration of 0.44 g was measured at ground level and extensive minor damage occurred; only minor injuries were reported. A fairly well-constrained fault-plane solution of the main shock and distribution of the aftershocks indicate that left-reverse-oblique slip occurred on west-northwest-trending, north-dipping reverse faults; inadequate dip control precludes good correlation with any one of several mapped faults. Had the earthquake been larger and rupture propagated to the southeast or a greater distance to the northwest, it could have posed a hazard to oilfield operations. The fault-plane solution and aftershock pattern closely fit the model of regional deformation and the solution closely resembles those of five previously mapped events located within a 15-km radius.

  13. Insights into induced earthquakes and aftershock activity with in-situ measurements of seismic velocity variations in an active underground mine

    NASA Astrophysics Data System (ADS)

    Brenguier, F.; Olivier, G.; Campillo, M.; Roux, P.; Shapiro, N.; Lynch, R.

    2015-12-01

    The behaviour of the crust shortly after large earthquakes has been the subject of numerous studies, but many co- and post-seismic processes remain poorly understood. Damage and healing of the bulk rock mass, post-seismic deformation and the mechanisms of earthquake triggering are still not well understood. These processes are important to properly model and understand the behaviour of faults and earthquake cycles.In this presentation, we will show how in-situ measurements of seismic velocity variations have given new insights into these co- and post-seismic processes. An experiment was performed where a blast was detonated in a tunnel in an underground mine, while seismic velocity variations were accurately (0.005 %) measured with ambient seismic noise correlations. Additionally, aftershock activity was examined and the influence of the removal of a piece of solid rock was estimated with elastic static stress modelling. The majority of the aftershocks were delayed with respect to the passing of the dynamic waves from the blast, while the locations of the aftershocks appeared clustered and not homogeneously spread around the blast location. A significant velocity drop is visible during the time of the blast, which is interpreted as co-seismic damage and plastic deformation. These non-elastic effects are healed by the confining stresses over a period of 5 days until the seismic velocity converges to a new baseline level. The instantaneous weakening and gradual healing observed from the velocity variations are qualitatively similar to results reported in laboratory studies. The change in the baseline level of the seismic velocity before and after the blast indicate a change in the static stress that is comparable to the results of elastic static stress modelling. The differences between the elastic model predictions and the seismic velocity variations could be due to zones of fractured rock, indicated by the spatial clustering of the aftershocks, that are not

  14. A hypocentral version of the space-time ETAS model

    NASA Astrophysics Data System (ADS)

    Guo, Yicun; Zhuang, Jiancang; Zhou, Shiyong

    2015-10-01

    The space-time Epidemic-Type Aftershock Sequence (ETAS) model is extended by incorporating the depth component of earthquake hypocentres. The depths of the direct offspring produced by an earthquake are assumed to be independent of the epicentre locations and to follow a beta distribution, whose shape parameter is determined by the depth of the parent event. This new model is verified by applying it to the Southern California earthquake catalogue. The results show that the new model fits data better than the original epicentre ETAS model and that it provides the potential for modelling and forecasting seismicity with higher resolutions.

  15. Comparison of main-shock and aftershock fragility curves developed for New Zealand and US buildings

    USGS Publications Warehouse

    Uma, S.R.; Ryu, H.; Luco, N.; Liel, A.B.; Raghunandan, M.

    2011-01-01

    Seismic risk assessment involves the development of fragility functions to express the relationship between ground motion intensity and damage potential. In evaluating the risk associated with the building inventory in a region, it is essential to capture 'actual' characteristics of the buildings and group them so that 'generic building types' can be generated for further analysis of their damage potential. Variations in building characteristics across regions/countries largely influence the resulting fragility functions, such that building models are unsuitable to be adopted for risk assessment in any other region where a different set of building is present. In this paper, for a given building type (represented in terms of height and structural system), typical New Zealand and US building models are considered to illustrate the differences in structural model parameters and their effects on resulting fragility functions for a set of main-shocks and aftershocks. From this study, the general conclusion is that the methodology and assumptions used to derive basic capacity curve parameters have a considerable influence on fragility curves.

  16. Aftershock mechanisms from the 2010 Mw 8.8 Maule, Chile earthquake: detailed analysis using full waveform inversion

    NASA Astrophysics Data System (ADS)

    Rietbrock, A.; Hicks, S. P.; Chagas, B.; Detzel, H. A.

    2014-12-01

    Since the earthquake rupture process is extremely heterogeneous, it is vital to understand how structural variations in the overriding plate and downgoing slab may control slip style along the subduction megathrust. The large-scale 3-D geometry of subduction plate boundaries is rapidly becoming well understood; however, the nature of any finer-scale structure along the plate interface remains elusive. A detailed study of earthquake source mechanisms along a megathrust region can shed light on the nature of fine-scale structures along the megathrust. The Mw 8.8 Maule earthquake that struck central Chile in 2010 is the sixth largest earthquake ever recorded. Following the earthquake, there was an international deployment of seismic stations in the rupture area, making this one of the best datasets of an aftershock sequence following a large earthquake. This dataset provides a unique opportunity to perform a detailed study of megathrust earthquake source mechanisms. Based on a high-resolution 3-D velocity model and robust earthquake locations [Hicks et al., 2014], we calculate regional moment tensors using the ISOLA software package [Sokos & Zahradnik, 2008]. We incorporate accelerometer recordings, important for constraining solutions of large earthquakes in the overriding plate. We also validate the robustness of our solutions by assessing the consistency of mechanisms with P-wave polarities observed at both onshore and offshore seismic stations, and compare them to already published solutions. We find that accurate earthquake locations are vital for the fine-scale interpretation of focal mechanisms, particularly for offshore events. Our results show that most moment tensor solutions with thrusting mechanisms have a nodal plane dipping parallel to the subducting plate interface. Interestingly, we also find earthquakes with normal faulting mechanisms lying along to the megathrust plate interface in the south of the rupture area. This finding suggests that megathrust

  17. Depth-dependent structure of the Landers fault zone from trapped waves generated by aftershocks

    NASA Astrophysics Data System (ADS)

    Li, Yong-Gang; Vidale, John E.; Aki, Keiiti; Xu, Fei

    2000-03-01

    We delineate the internal structure of the Johnson Valley and Kickapoo faults (Landers southern rupture) at seismogenic depth using fault zone trapped waves generated by aftershocks. Trapped waves recorded at the dense linear seismic arrays deployed across and along the surface breaks of the 1992 M7.5 Landers earthquake show large amplitudes and dispersive wave trains following the S waves. Group velocities of trapped waves measured from multiple band-pass-filtered seismograms for aftershocks occurring at different depths between 1.8 km and 8.2 km show an increase in velocity with depth. Velocities range from 1.9 km/s at 4 Hz to 2.6 km/s at 1 Hz for shallow events, while for deep events, velocities range from 2.3 km/s at 4 Hz to 3.1 km/s at 1 Hz. Coda-normalized amplitude spectra of trapped waves peak in amplitudes at 3-4 Hz for stations located close to the fault trace. The amplitude decays rapidly with the station offset from the fault zone. Normalized amplitudes also decrease with distance along the fault, giving an apparent Q of 30 for shallow events and 50 for deep events. We evaluated depth-dependent fault zone structure and its uncertainty from these measurements plus our previous results from near-surface explosion-excited trapped waves [Li et al., 1999] in a systematic model parameter-searching procedure using a three-dimensional (3-D) finite difference computer code [Graves, 1996]. Our best model of the Landers fault zone is 250 m wide at the surface, tapering to 100-150 m at 8.2 km depth. The shear velocity within the fault zone increases from 1.0 to 2.5 km/s and Q increases from 20 to 60 in this depth range. Fault zone shear velocities are reduced by 35 to 45% from those of the surrounding rock and also vary along the fault zone with an increase of ˜10% near ends of the southern rupture zone.

  18. Rupture processes of the 2015 Mw 7.9 Gorkha earthquake and its Mw 7.3 aftershock and their implications on the seismic risk

    NASA Astrophysics Data System (ADS)

    Liu, Chengli; Zheng, Yong; Wang, Rongjiang; Shan, Bin; Xie, Zujun; Xiong, Xiong; Ge, Can

    2016-07-01

    The rupture processes of the 2015 April 25 Gorkha earthquake and its strongest aftershock occurred on May 12 in Nepal are investigated by joint inversion of seismological and geodetic data. Synthetic test shows that the sedimentary layers in the source region play an important role in the rupture process inversion. Our optimized model of the mainshock shows that the rupture has a unilateral propagation pattern. The dominant mechanism is pure thrust with maximum slip of 5.8 m, the rupture scale extends 60 km along dip and 150 km along strike, and the largest static stress change is 7.6 MPa. The total seismic moment is 7.87 × 1020 N m, equivalent to Mw 7.9. Most seismic moment was released within 80 s and the majority seismic moment was released at the first 40 s. The rupture propagated in main slip asperity with a velocity of 3.0 km/s. The strong aftershock magnitude is about Mw 7.3, and the peak slip is about 5.0 m, close to the peak slip of the mainshock. Moreover, the slips of the mainshock and the aftershocks are in good complementary, suggesting a triggering relationship between them. Considering the strain accumulation, the Gorkha earthquake ruptured only part of the seismic gap alone, thus still poses high earthquake risk, especially in the west side of the mainshock rupture zone.

  19. Dependence of the aftershock flow on the main shock magnitude

    NASA Astrophysics Data System (ADS)

    Guglielmi, A. V.; Zavyalov, A. D.; Zotov, O. D.; Lavrov, I. P.

    2017-01-01

    Previously, we predicted and then observed in practice the property of aftershocks which consists in the statistically regular clustering of events in time during the first hours after the main shock. The characteristic quasi-period of clustering is three hours. This property is associated with the cumulative action of the surface waves converging to the epicenter, whereas the quasi-period is mainly determined by the time delay of the round-the-world seismic echo. The quasi-period varies from case to case. In the attempt to find the cause of this variability, we have statistically explored the probable dependence of quasi-period on the magnitude of the main shock. In this paper, we present the corresponding result of analyzing global seismicity from the USGS/NEIC earthquake catalog. We succeeded in finding a significant reduction in the quasiperiod of the strong earthquakes clustering with growth in the magnitude of the main shock. We suggest the interpretation of this regularity from the standpoint of the phenomenological theory of explosive instability. It is noted that the phenomenon of explosive instability is fairly common in the geophysical media. The examples of explosive instability in the radiation belt and magnetospheric tail are presented. The search for the parallels in the evolution of explosive instability in the lithosphere and magnetosphere of the Earth will enrich both the physics of the earthquakes and physics of the magnetospheric pulsations.

  20. A Nonparametric Bayesian Approach to Seismic Hazard Modeling Using the ETAS Framework

    NASA Astrophysics Data System (ADS)

    Ross, G.

    2015-12-01

    The epidemic-type aftershock sequence (ETAS) model is one of the most popular tools for modeling seismicity and quantifying risk in earthquake-prone regions. Under the ETAS model, the occurrence times of earthquakes are treated as a self-exciting Poisson process where each earthquake briefly increases the probability of subsequent earthquakes occurring soon afterwards, which captures the fact that large mainshocks tend to produce long sequences of aftershocks. A triggering kernel controls the amount by which the probability increases based on the magnitude of each earthquake, and the rate at which it then decays over time. This triggering kernel is usually chosen heuristically, to match the parametric form of the modified Omori law for aftershock decay. However recent work has questioned whether this is an appropriate choice. Since the choice of kernel has a large impact on the predictions made by the ETAS model, avoiding misspecification is crucially important. We present a novel nonparametric version of ETAS which avoids making parametric assumptions, and instead learns the correct specification from the data itself. Our approach is based on the Dirichlet process, which is a modern class of Bayesian prior distribution which allows for efficient inference over an infinite dimensional space of functions. We show how our nonparametric ETAS model can be fit to data, and present results demonstrating that the fit is greatly improved compared to the standard parametric specification. Additionally, we explain how our model can be used to perform probabilistic declustering of earthquake catalogs, to classify earthquakes as being either aftershocks or mainshocks. and to learn the causal relations between pairs of earthquakes.

  1. Modeling of the Nano- and Picoseismicity Rate Changes Resulting from Static Stress Triggering due to Small (MW2.2) Event Recorded at Mponeng Deep Gold Mine, South Africa

    NASA Astrophysics Data System (ADS)

    Kozlowska, M.; Orlecka-Sikora, B.; Kwiatek, G.; Boettcher, M. S.; Dresen, G. H.

    2014-12-01

    Static stress changes following large earthquakes are known to affect the rate and spatio-temporal distribution of the aftershocks. Here we utilize a unique dataset of M ≥ -3.4 earthquakes following a MW 2.2 earthquake in Mponeng gold mine, South Africa, to investigate this process for nano- and pico- scale seismicity at centimeter length scales in shallow, mining conditions. The aftershock sequence was recorded during a quiet interval in the mine and thus enabled us to perform the analysis using Dietrich's (1994) rate and state dependent friction law. The formulation for earthquake productivity requires estimation of Coulomb stress changes due to the mainshock, the reference seismicity rate, frictional resistance parameter, and the duration of aftershock relaxation time. We divided the area into six depth intervals and for each we estimated the parameters and modeled the spatio-temporal patterns of seismicity rates after the stress perturbation. Comparing the modeled patterns of seismicity with the observed distribution we found that while the spatial patterns match well, the rate of modeled aftershocks is lower than the observed rate. To test our model, we used four metrics of the goodness-of-fit evaluation. Testing procedure allowed rejecting the null hypothesis of no significant difference between seismicity rates only for one depth interval containing the mainshock, for the other, no significant differences have been found. Results show that mining-induced earthquakes may be followed by a stress relaxation expressed through aftershocks located on the rupture plane and in regions of positive Coulomb stress change. Furthermore, we demonstrate that the main features of the temporal and spatial distribution of very small, mining-induced earthquakes at shallow depths can be successfully determined using rate- and state-based stress modeling.

  2. Global Omori law decay of triggered earthquakes: large aftershocks outside the classical aftershock zone

    USGS Publications Warehouse

    Parsons, Tom

    2002-01-01

    Triggered earthquakes can be large, damaging, and lethal as evidenced by the 1999 shocks in Turkey and the 2001 earthquakes in El Salvador. In this study, earthquakes with Ms ≥ 7.0 from the Harvard centroid moment tensor (CMT) catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected. About 61% of earthquakes that occurred near (defined as having shear stress change ∣Δτ∣ ≥ 0.01 MPa) the Ms ≥ 7.0 shocks are associated with calculated shear stress increases, while ∼39% are associated with shear stress decreases. If earthquakes associated with calculated shear stress increases are interpreted as triggered, then such events make up at least 8% of the CMT catalog. Globally, these triggered earthquakes obey an Omori law rate decay that lasts between ∼7–11 years after the main shock. Earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid. Omori's law is one of the few time-predictable patterns evident in the global occurrence of earthquakes. If large triggered earthquakes habitually obey Omori's law, then their hazard can be more readily assessed. The characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of Ms ≥ 7.0. I show an example application to the M = 7.7 13 January 2001 El Salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than Coulomb stress change calculations.

  3. Global Omori law decay of triggered earthquakes: Large aftershocks outside the classical aftershock zone

    USGS Publications Warehouse

    Parsons, T.

    2002-01-01

    Triggered earthquakes can be large, damaging, and lethal as evidenced by the 1999 shocks in Turkey and the 2001 earthquakes in El Salvador. In this study, earthquakes with Ms ≥ 7.0 from the Harvard centroid moment tensor (CMT) catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected. About 61% of earthquakes that occured near (defined as having shear stress change |Δ| 0.01 MPa) the Ms ≥ 7.0 shocks are associated with calculated shear stress increases, while ~39% are associated with shear stress decreases. If earthquakes associated with calculated shear stress increases are interpreted as triggered, then such events make up at least 8% of the CMT catalog. Globally, these triggered earthquakes obey an Omori law rate decay that lasts between ~7-11 years after the main shock. Earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid. Omori's law is one of the few time-predictable patterns evident in the global occurrence of earthquakes. If large triggered earthquakes habitually obey Omori's law, then their hazard can be more readily assessed. The characteristics rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of Ms ≥7.0. I show an example application to the M = 7.7 13 January 2001 El Salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than Coulomb stress change calculations.

  4. Quantitative description of induced seismic activity before and after the 2011 Tohoku-Oki earthquake by nonstationary ETAS models

    NASA Astrophysics Data System (ADS)

    Kumazawa, Takao; Ogata, Yosihiko

    2013-12-01

    The epidemic-type aftershock sequence (ETAS) model is extended for application to nonstationary seismic activity, including transient swarm activity or seismicity anomalies, in a seismogenic region. The time-dependent rates of both background seismicity and aftershock productivity in the ETAS model are optimally estimated from hypocenter data. These rates can provide quantitative evidence for abrupt or gradual changes in shear stress and/or fault strength due to aseismic transient causes such as triggering by remote earthquakes, slow slips, or fluid intrusions within the region. This extended model is applied to data sets from several seismic events including swarms that were induced by the M9.0 Tohoku-Oki earthquake of 2011.

  5. Probabilistic topic modeling for the analysis and classification of genomic sequences

    PubMed Central

    2015-01-01

    Background Studies on genomic sequences for classification and taxonomic identification have a leading role in the biomedical field and in the analysis of biodiversity. These studies are focusing on the so-called barcode genes, representing a well defined region of the whole genome. Recently, alignment-free techniques are gaining more importance because they are able to overcome the drawbacks of sequence alignment techniques. In this paper a new alignment-free method for DNA sequences clustering and classification is proposed. The method is based on k-mers representation and text mining techniques. Methods The presented method is based on Probabilistic Topic Modeling, a statistical technique originally proposed for text documents. Probabilistic topic models are able to find in a document corpus the topics (recurrent themes) characterizing classes of documents. This technique, applied on DNA sequences representing the documents, exploits the frequency of fixed-length k-mers and builds a generative model for a training group of sequences. This generative model, obtained through the Latent Dirichlet Allocation (LDA) algorithm, is then used to classify a large set of genomic sequences. Results and conclusions We performed classification of over 7000 16S DNA barcode sequences taken from Ribosomal Database Project (RDP) repository, training probabilistic topic models. The proposed method is compared to the RDP tool and Support Vector Machine (SVM) classification algorithm in a extensive set of trials using both complete sequences and short sequence snippets (from 400 bp to 25 bp). Our method reaches very similar results to RDP classifier and SVM for complete sequences. The most interesting results are obtained when short sequence snippets are considered. In these conditions the proposed method outperforms RDP and SVM with ultra short sequences and it exhibits a smooth decrease of performance, at every taxonomic level, when the sequence length is decreased. PMID:25916734

  6. The systematic study of the stability of forecasts in the rate- and state-dependent model.

    NASA Astrophysics Data System (ADS)

    De Gaetano, D.; McCloskey, J.; Nalbant, S.

    2012-04-01

    Numerous observations have shown a general spatial correlation between positive Coulomb failure stress changes due to an earthquake and the locations of aftershocks. However this correlation does not give any indication of the rate from which we can infer the magnitude using the Gutenberg-Richter law. Dieterich's rate- and state-dependent model can be used to obtain a forecast of the observed aftershock rate for the space and time evolution of seismicity caused by stress changes applied to an infinite population of nucleating patches. The seismicity rate changes on this model depend on eight parameters: the stressing rate, the amplitude of the stress perturbation, the physical constitutive properties of faults, the spatial parameters (location and radii of the cells), the start and duration of each of the temporal windows as well as the background seismicity rate. The background seismicity is obtained from the epidemic type aftershock sequence model. We use the 1992 Landers earthquake as a case study, using the Southern California Earthquake Data Centre (SCEDC) catalogue, to examine if Dieterich's rate- and state-dependent model can forecast the aftershock seismicity rate. A systematic study is performed on a range of values on all the parameters to test the forecasting ability of this model. The results obtained suggest variable success in forecasting, when varying the values for the parameters, with the spatial and temporal parameters being the most sensitive. Dieterich's rate- and state-dependent model is compared with a well studied null hypothesis, the Omori-Utsu law. This law describes the aftershock rate as a power law in time following the main shock and depends on only three parameters: the aftershock productivity, the elapsed time since the main shock and the constant time shift, all of which can be estimated in the early part of the aftershock sequence and then extrapolated to give a long term rate forecast. All parameters are estimated using maximum

  7. Decay of aftershock density with distance does not indicate triggering by dynamic stress

    USGS Publications Warehouse

    Richards-Dinger, K.; Stein, R.S.; Toda, S.

    2010-01-01

    Resolving whether static or dynamic stress triggers most aftershocks and subsequent mainshocks is essential to understand earthquake interaction and to forecast seismic hazard. Felzer and Brodsky examined the distance distribution of earthquakes occurring in the first five minutes after 2 ≤ M  M  M ≥ 2 aftershocks showed a uniform power-law decay with slope −1.35 out to 50 km from the mainshocks. From this they argued that the distance decay could be explained only by dynamic triggering. Here we propose an alternative explanation for the decay, and subject their hypothesis to a series of tests, none of which it passes. At distances more than 300 m from the 2 ≤  M< 3 mainshocks, the seismicity decay 5 min before the mainshocks is indistinguishable from the decay five minutes afterwards, indicating that the mainshocks have no effect at distances outside their static triggering range. Omori temporal decay, the fundamental signature of aftershocks, is absent at distances exceeding 10 km from the mainshocks. Finally, the distance decay is found among aftershocks that occur before the arrival of the seismic wave front from the mainshock, which violates causality. We argue that Felzer and Brodsky implicitly assume that the first of two independent aftershocks along a fault rupture triggers the second, and that the first of two shocks in a creep- or intrusion-driven swarm triggers the second, when this need not be the case.

  8. Analysis of strong ground motions and site effects at Kantipath, Kathmandu, from 2015 Mw 7.8 Gorkha, Nepal, earthquake and its aftershocks

    NASA Astrophysics Data System (ADS)

    Dhakal, Yadab P.; Kubo, Hisahiko; Suzuki, Wataru; Kunugi, Takashi; Aoi, Shin; Fujiwara, Hiroyuki

    2016-04-01

    Strong ground motions from the 2015 Mw 7.8 Gorkha, Nepal, earthquake and its eight aftershocks recorded by a strong-motion seismograph at Kantipath (KATNP), Kathmandu, were analyzed to assess the ground-motion characteristics and site effects at this location. Remarkably large elastic pseudo-velocity responses exceeding 300 cm/s at 5 % critical damping were calculated for the horizontal components of the mainshock recordings at peak periods of 4-5 s. Conversely, the short-period ground motions of the mainshock were relatively weak despite the proximity of the site to the source fault. The horizontal components of all large-magnitude (Mw ≥ 6.3) aftershock recordings showed peak pseudo-velocity responses at periods of 3-4 s. Ground-motion prediction equations (GMPEs) describing the Nepal Himalaya region have not yet been developed. A comparison of the observational data with GMPEs for Japan showed that with the exception of the peak ground acceleration (PGA) of the mainshock, the observed PGAs and peak ground velocities at the KATNP site are generally well described by the GMPEs for crustal and plate interface events. A comparison of the horizontal-to-vertical ( H/ V) spectral ratios for the S-waves of the mainshock and aftershock recordings suggested that the KATNP site experienced a considerable nonlinear site response, which resulted in the reduced amplitudes of short-period ground motions. The GMPEs were found to underestimate the response values at the peak periods (approximately 4-5 s) of the large-magnitude events. The deep subsurface velocity model of the Kathmandu basin has not been well investigated. Therefore, a one-dimensional velocity model was constructed for the deep sediments beneath the recording station based on an analysis of the H/ V spectral ratios for S-wave coda from aftershock recordings, and it was revealed that the basin sediments strongly amplified the long-period components of the ground motions of the mainshock and large

  9. WaveHRL: a high resolution, modular seismic event system and its application to the L'Aquila 2009 earthquake sequence

    NASA Astrophysics Data System (ADS)

    Mulder, T.; Brillon, C.; Bentkowski, W.; White, M.; Rosenberger, A.; Rogers, G. C.; Vernon, F.; Kao, H.

    2011-12-01

    The magnitude 7.7 thrust earthquake that occurred on 2012 Oct 28 offshore of Haida Gwaii (formerly the Queen Charlotte Islands), in British Columbia, Canada, produced a rich and on-going aftershock sequence. Ten months of aftershock events are determined from analyst reviewed solutions and automatic detectors and locators. For automated solutions, rotating the waveforms and running P and S wave filters (Rosenberger, 2010) over them produced phase arrivals for an improved catalogue of aftershocks compared to using a traditional signal to noise ratio detector on standard vertical and horizontal component seismograms. The automated aftershock locations from the rotated waveforms are compared to the automated locations from the standard vertical and horizontal waveforms and to analyst locations (which are generally M>2.5). The best of the automated solutions are comparable in quality to analyst solutions and much more numerous making this a viable method of processing extensive aftershock sequences. They outline a region approximately 50 km wide and 100 km long, with the aftershocks in two parallel bands. Most of the aftershocks are not on the rupture surface but are in the overlying or underlying plates. It is thought that this earthquake represents the Pacific plate thrusting underneath the North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault. Due to the one-sided station distribution on land, depth trades off with distance offshore, resulting in poor depth determinations. However, using ocean bottom seismometers deployed early in the aftershock sequence, depth resolution was significantly improved. First motion focal North America plate with the rupture surface lying beneath the sedimentary Queen Charlotte terrace and terminating to the east in the vicinity of the Queen Charlotte fault.mechanisms for a portion of the aftershock sequence are compared

  10. A sparse model based detection of copy number variations from exome sequencing data

    PubMed Central

    Duan, Junbo; Wan, Mingxi; Deng, Hong-Wen; Wang, Yu-Ping

    2016-01-01

    Goal Whole-exome sequencing provides a more cost-effective way than whole-genome sequencing for detecting genetic variants such as copy number variations (CNVs). Although a number of approaches have been proposed to detect CNVs from whole-genome sequencing, a direct adoption of these approaches to whole-exome sequencing will often fail because exons are separately located along a genome. Therefore, an appropriate method is needed to target the specific features of exome sequencing data. Methods In this paper a novel sparse model based method is proposed to discover CNVs from multiple exome sequencing data. First, exome sequencing data are represented with a penalized matrix approximation, and technical variability and random sequencing errors are assumed to follow a generalized Gaussian distribution. Second, an iteratively re-weighted least squares algorithm is used to estimate the solution. Results The method is tested and validated on both synthetic and real data, and compared with other approaches including CoNIFER, XHMM and cn.MOPS. The test demonstrates that the proposed method outperform other approaches. Conclusion The proposed sparse model can detect CNVs from exome sequencing data with high power and precision. Significance Sparse model can target the specific features of exome sequencing data. The software codes are freely available at http://www.tulane.edu/wyp/software/ExonCNV.m PMID:26258935

  11. Models of hydrocarbon-bearing sequences of West Siberia

    SciTech Connect

    Mkrtohyan, O.M.; Gogonenkov, G.N.; Pavlov, N.E. )

    1991-03-01

    The West Siberian province located within a young plate (platform) is one of the largest in the world in size, reserves, number of unique fields, and hydrocarbon production. The southern, central, and western areas of the province are dominantly oil-bearing, the northern portion gas-bearing. All commercial reserves are within the Devonian-Cenomanian stratigraphic interval. Small accumulations in fractured-vuggy Devon-Carboniferous rocks are located in the zone of unconformity between this sequence and the Jurassic. The potential of the pre-plate middle Paleozoic, platform upper Paleozoic, and Triassic sequences recognized by seismic data in the northern, deepest, part of the plate is not known yet. Most hydrocarbon pools are located in the Jurassic-Cretaceous hydrocarbon-bearing sequences (HBS) within the plate cover. Structural-depositional oil accumulations with very changeable flow rates, a large stratigraphic-depositional accumulation in high permeability basal (quartz) reservoirs, and an oil-condensate and a multiple-pool structural gas field are discovered in the Middle Jurassic composed of potential continental coal-bearing and marine deposits. In most HBS, there is still a prospect of discovering new hydrocarbon pools including pools in more complex traps.

  12. Chapter D. The Loma Prieta, California, Earthquake of October 17, 1989 - Aftershocks and Postseismic Effects

    USGS Publications Warehouse

    Reasenberg, Paul A.

    1997-01-01

    While the damaging effects of the earthquake represent a significant social setback and economic loss, the geophysical effects have produced a wealth of data that have provided important insights into the structure and mechanics of the San Andreas Fault system. Generally, the period after a large earthquake is vitally important to monitor. During this part of the seismic cycle, the primary fault and the surrounding faults, rock bodies, and crustal fluids rapidly readjust in response to the earthquake's sudden movement. Geophysical measurements made at this time can provide unique information about fundamental properties of the fault zone, including its state of stress and the geometry and frictional/rheological properties of the faults within it. Because postseismic readjustments are rapid compared with corresponding changes occurring in the preseismic period, the amount and rate of information that is available during the postseismic period is relatively high. From a geophysical viewpoint, the occurrence of the Loma Prieta earthquake in a section of the San Andreas fault zone that is surrounded by multiple and extensive geophysical monitoring networks has produced nothing less than a scientific bonanza. The reports assembled in this chapter collectively examine available geophysical observations made before and after the earthquake and model the earthquake's principal postseismic effects. The chapter covers four broad categories of postseismic effect: (1) aftershocks; (2) postseismic fault movements; (3) postseismic surface deformation; and (4) changes in electrical conductivity and crustal fluids.

  13. Human Immunodeficiency Virus Reverse Transcriptase and Protease Sequence Database: an expanded data model integrating natural language text and sequence analysis programs.

    PubMed

    Kantor, R; Machekano, R; Gonzales, M J; Dupnik, K; Schapiro, J M; Shafer, R W

    2001-01-01

    The HIV Reverse Transcriptase and Protease Sequence Database is an on-line relational database that catalogs evolutionary and drug-related sequence variation in the human immunodeficiency virus (HIV) reverse transcriptase (RT) and protease enzymes, the molecular targets of anti-HIV therapy (http://hivdb.stanford.edu). The database contains a compilation of nearly all published HIV RT and protease sequences, including submissions from International Collaboration databases and sequences published in journal articles. Sequences are linked to data about the source of the sequence sample and the antiretroviral drug treatment history of the individual from whom the isolate was obtained. During the past year 3500 sequences have been added and the data model has been expanded to include drug susceptibility data on sequenced isolates. Database content has also been integrated with didactic text and the output of two sequence analysis programs.

  14. An Activation-Based Model of Routine Sequence Errors

    DTIC Science & Technology

    2015-04-01

    time it is used, and models the neuronal noise found in the human brain. Perception and Action Finally, the model interacts with the world using ACT-R...original memory for goals model is the depth to which prim- ing is utilized by the model. In the MFG model, priming derived from explicit correspondences...Trafton, J. G. (2013). The role of familiarity, priming and perception in similarity judgments. In Pro- ceedings of the Annual Meeting of the

  15. Clustered and transient earthquake sequences in mid-continents

    NASA Astrophysics Data System (ADS)

    Liu, M.; Stein, S. A.; Wang, H.; Luo, G.

    2012-12-01

    Earthquakes result from sudden release of strain energy on faults. On plate boundary faults, strain energy is constantly accumulating from steady and relatively rapid relative plate motion, so large earthquakes continue to occur so long as motion continues on the boundary. In contrast, such steady accumulation of stain energy does not occur on faults in mid-continents, because the far-field tectonic loading is not steadily distributed between faults, and because stress perturbations from complex fault interactions and other stress triggers can be significant relative to the slow tectonic stressing. Consequently, mid-continental earthquakes are often temporally clustered and transient, and spatially migrating. This behavior is well illustrated by large earthquakes in North China in the past two millennia, during which no single large earthquakes repeated on the same fault segments, but moment release between large fault systems was complementary. Slow tectonic loading in mid-continents also causes long aftershock sequences. We show that the recent small earthquakes in the Tangshan region of North China are aftershocks of the 1976 Tangshan earthquake (M 7.5), rather than indicators of a new phase of seismic activity in North China, as many fear. Understanding the transient behavior of mid-continental earthquakes has important implications for assessing earthquake hazards. The sequence of large earthquakes in the New Madrid Seismic Zone (NMSZ) in central US, which includes a cluster of M~7 events in 1811-1812 and perhaps a few similar ones in the past millennium, is likely a transient process, releasing previously accumulated elastic strain on recently activated faults. If so, this earthquake sequence will eventually end. Using simple analysis and numerical modeling, we show that the large NMSZ earthquakes may be ending now or in the near future.

  16. Aperiodic sequences and magnetic models: non-universal critical behavior within mean-field approximation

    NASA Astrophysics Data System (ADS)

    Branco, Nilton; Faria, Maicon; Tragtenberg, Marcelo

    2007-03-01

    We study the Ising model on a Bethe lattice, such that the exchange constant can assume two values, according to two-letter aperiodic sequences. Critical temperatures and exponents are calculated for three different sequences: Fibonacci, period-doubling and two-letter Rudin-Shapiro ones. These sequences are found to be irrelevant, marginal, and relevant, respectively, in the renormalization-group sense. The Fibonacci sequence presents the same critical behavior as for the uniform model and no log-periodic behavior is observed. For the marginal sequence, critical exponents depend on the ratio between the two possible exchange constants and a log-periodic behavior is clearly determined. Due to computational constraints, our results are not as precise for the Rudin-Shapiro sequence but we obtain evidence that the exponents are different from the classical ones and do not depend on the ratio between the exchange constants.

  17. Temporal evolution of earthquake sequences (swarms) in the Central Volcanic Region, New Zealand

    NASA Astrophysics Data System (ADS)

    Jacobs, K. M.; Smith, E. G.; Savage, M. K.

    2009-12-01

    We examine the temporal evolution of earthquake sequences in the Central Volcanic Region of New Zealand as a step towards probabilistic modelling. We characterize 257 sequences with at least four events selected from the GeoNet earthquake catalog between 1987 and 2009 with an inferred completeness magnitude of 2.5. We categorize 14 as mainshock-aftershock (MS-AS), including four of the ten largest sequences. We analyze sequences by size (4 to 831 events), maximum magnitude (2.53 to 6.14), duration (minutes to 35 days), and other parameters including moment release with time, magnitude histories, inter-event time differences, and spatial relationships. In particular we closely examine the position and size of the maximum magnitude event and its relation to the size and development of each sequence. Sequences with mainshock magnitudes of M=5.0 or greater all have 100 or more earthquakes (5 sequences, including 3 MS-AS). Sequences with a mainshock magnitude below 3.0 have less than 20 earthquakes (60 sequences). We use average inter-event time differences to look at development of sequences in time. While there is variability between sequences they generally fit three basic patterns (Fig.). We have also searched for possible triggering of the sequences by large global (M=7.0+) and moderate New Zealand (M=6.0+) earthquakes. While some sequences follow large earthquakes closely in time, we cannot rule out the possibility that this timing is random. Average inter-event times are plotted against time normalized to sequence duration for three sequences A) classic MS-AS sequence with decaying rate (increasing inter-event time); B) swarm whose rate accelerates towards the end of the sequence (decreasing inter-event time); C) sharp increase in rate (decrease in inter-event time) followed by steady decrease (seen for both swarm type and some foreshock-MS-AS sequences).

  18. High frequencies are a critical component of aftershock triggering at <100-150 km (Invited)

    NASA Astrophysics Data System (ADS)

    Felzer, K. R.

    2010-12-01

    Triggered earthquakes at large distances from the mainshock have been observed to closely follow the arrival of ~0.03-0.6 Hz surface waves (Hill, 2008). Triggering by body waves at these distances is generally not observed. At distances closer than 50-100 km, however, surface waves are not well developed and have minimal amplitude. Thus triggering at these distances is presumably accomplished by static stress change and/or by body waves via a mechanism that does not work at further distances. Pollitz (2006) demonstrated that slow slip events on the San Andreas fault do not trigger many aftershocks, suggesting that static stresses alone are not effective triggers, while Felzer and Brodsky (2006) demonstrated that dynamic stresses alone do appear to trigger aftershocks at least in the 10--50 km range. Yet Parsons and Velasco (2009) found that underground nuclear tests, which are essentially dynamic-only sources, do not produce aftershocks at regional distances. Here we demonstrate that Southern California quarry blasts also fail to produce aftershocks. Both nuclear tests and quarry blasts are depleted in high frequency energy in comparison to tectonic earthquakes (Su et al. 1991; Allman et al. 2008). Therefore the observation that both slow slip events and blasts fail to trigger many aftershocks suggests that the missing ingredient of high frequency body wave energy plays a critical role in the triggering process. Quarry blast spectra data and scaling considerations allow the critical triggering frequency to be constrained to > 20-60 Hz. Energy in this frequency band may be expected to persist at depth at least out to 100 km (Leary, 1995). Huc and Main (2003) found that aftershock triggering by global earthquakes follows a continuous decay curve out to ~150 km, suggesting that triggering by high frequency body waves might extend this far. At much further distances the high frequencies are likely attenuated, explaining why only low frequency surface wave triggering

  19. Next-Generation Phylogeography: A Targeted Approach for Multilocus Sequencing of Non-Model Organisms

    PubMed Central

    Puritz, Jonathan B.; Addison, Jason A.; Toonen, Robert J.

    2012-01-01

    The field of phylogeography has long since realized the need and utility of incorporating nuclear DNA (nDNA) sequences into analyses. However, the use of nDNA sequence data, at the population level, has been hindered by technical laboratory difficulty, sequencing costs, and problematic analytical methods dealing with genotypic sequence data, especially in non-model organisms. Here, we present a method utilizing the 454 GS-FLX Titanium pyrosequencing platform with the capacity to simultaneously sequence two species of sea star (Meridiastra calcar and Parvulastra exigua) at five different nDNA loci across 16 different populations of 20 individuals each per species. We compare results from 3 populations with traditional Sanger sequencing based methods, and demonstrate that this next-generation sequencing platform is more time and cost effective and more sensitive to rare variants than Sanger based sequencing. A crucial advantage is that the high coverage of clonally amplified sequences simplifies haplotype determination, even in highly polymorphic species. This targeted next-generation approach can greatly increase the use of nDNA sequence loci in phylogeographic and population genetic studies by mitigating many of the time, cost, and analytical issues associated with highly polymorphic, diploid sequence markers. PMID:22470543

  20. A Statistical Model of Protein Sequence Similarity and Function Similarity Reveals Overly-Specific Function Predictions

    PubMed Central

    Kolker, Eugene

    2009-01-01

    Background Predicting protein function from primary sequence is an important open problem in modern biology. Not only are there many thousands of proteins of unknown function, current approaches for predicting function must be improved upon. One problem in particular is overly-specific function predictions which we address here with a new statistical model of the relationship between protein sequence similarity and protein function similarity. Methodology Our statistical model is based on sets of proteins with experimentally validated functions and numeric measures of function specificity and function similarity derived from the Gene Ontology. The model predicts the similarity of function between two proteins given their amino acid sequence similarity measured by statistics from the BLAST sequence alignment algorithm. A novel aspect of our model is that it predicts the degree of function similarity shared between two proteins over a continuous range of sequence similarity, facilitating prediction of function with an appropriate level of specificity. Significance Our model shows nearly exact function similarity for proteins with high sequence similarity (bit score >244.7, e-value >1e−62, non-redundant NCBI protein database (NRDB)) and only small likelihood of specific function match for proteins with low sequence similarity (bit score <54.6, e-value <1e−05, NRDB). For sequence similarity ranges in between our annotation model shows an increasing relationship between function similarity and sequence similarity, but with considerable variability. We applied the model to a large set of proteins of unknown function, and predicted functions for thousands of these proteins ranging from general to very specific. We also applied the model to a data set of proteins with previously assigned, specific functions that were electronically based. We show that, on average, these prior function predictions are more specific (quite possibly overly-specific) compared to

  1. Lacustrine sequence stratigraphy and computer modeling of the Erlian fault basin, North China

    SciTech Connect

    Lin Changsong; Li Sitian; Ren Jianye; Zhang Yanmei )

    1996-01-01

    Erlian fault basin, a major oil prospecting and producing area in North China, comprises about 40 grabens and half grabens. The basin was formed by extension from Jurassic to Early Cretaceous and filled with more than 3000m thick of clastic lacustrine deposits. Based on the integrated analysis of seismic profiles, logging and cores, 5 sequence sets and 12 sequences, bounded by discontinuous, have been identified. Three types of lacustrine sequences have been identified: (1) deep lacustrine basin sequences, mainly consisting of sublacustrine fan and fan delta systems; (2) shallow lacustrine basin sequences, predominately composed of fan delta and braided delta systems and (3) shallow lacustrine and fluvial basin sequences. The sequence architecture and the basin filling evolution were controlled by the basin structural framework and lacustrine level changes. The computer modeling study by using the backstripping and forward modeling technique has shown that the major unconformities confining the sequences may be generated by the variation in tectonic subsidence rate caused by episodic lithospheric stretching. The model have also be used to predict the sequence architecture and the facies distribution in the basin.

  2. Lacustrine sequence stratigraphy and computer modeling of the Erlian fault basin, North China

    SciTech Connect

    Lin Changsong; Li Sitian; Ren Jianye; Zhang Yanmei

    1996-12-31

    Erlian fault basin, a major oil prospecting and producing area in North China, comprises about 40 grabens and half grabens. The basin was formed by extension from Jurassic to Early Cretaceous and filled with more than 3000m thick of clastic lacustrine deposits. Based on the integrated analysis of seismic profiles, logging and cores, 5 sequence sets and 12 sequences, bounded by discontinuous, have been identified. Three types of lacustrine sequences have been identified: (1) deep lacustrine basin sequences, mainly consisting of sublacustrine fan and fan delta systems; (2) shallow lacustrine basin sequences, predominately composed of fan delta and braided delta systems and (3) shallow lacustrine and fluvial basin sequences. The sequence architecture and the basin filling evolution were controlled by the basin structural framework and lacustrine level changes. The computer modeling study by using the backstripping and forward modeling technique has shown that the major unconformities confining the sequences may be generated by the variation in tectonic subsidence rate caused by episodic lithospheric stretching. The model have also be used to predict the sequence architecture and the facies distribution in the basin.

  3. Statistical discrimination of induced and tectonic earthquake sequences in Central and Eastern US based on waveform detected catalogs

    NASA Astrophysics Data System (ADS)

    Meng, X.; Daniels, C.; Smith, E.; Peng, Z.; Chen, X.; Wagner, L. S.; Fischer, K. M.; Hawman, R. B.

    2015-12-01

    Since 2001, the number of M>3 earthquakes increased significantly in Central and Eastern United States (CEUS), likely due to waste-water injection, also known as "induced earthquakes" [Ellsworth, 2013]. Because induced earthquakes are driven by short-term external forcing and hence may behave like earthquake swarms, which are not well characterized by branching point-process models, such as the Epidemic Type Aftershock Sequence (ETAS) model [Ogata, 1988]. In this study we focus on the 02/15/2014 M4.1 South Carolina and the 06/16/2014 M4.3 Oklahoma earthquakes, which likely represent intraplate tectonic and induced events, respectively. For the South Carolina event, only one M3.0 aftershock is identified by the ANSS catalog, which may be caused by a lack of low-magnitude events in this catalog. We apply a recently developed matched filter technique to detect earthquakes from 02/08/2014 to 02/22/2014 around the epicentral region. 15 seismic stations (both permanent and temporary USArray networks) within 100 km of the mainshock are used for detection. The mainshock and aftershock are used as templates for the initial detection. Newly detected events are employed as new templates, and the same detection procedure repeats until no new event can be added. Overall we have identified more than 10 events, including one foreshock occurred ~11 min before the M4.1 mainshock. However, the numbers of aftershocks are still much less than predicted with the modified Bath's law. For the Oklahoma event, we use 1270 events from the ANSS catalog and 182 events from a relocated catalog as templates to scan through continuous recordings 3 days before to 7 days after the mainshock. 12 seismic stations within the vicinity of the mainshock are included in the study. After obtaining more complete catalogs for both sequences, we plan to compare the statistical parameters (e.g., b, a, K, and p values) between the two sequences, as well as their spatial-temporal migration pattern, which may

  4. A convolutional code-based sequence analysis model and its application.

    PubMed

    Liu, Xiao; Geng, Xiaoli

    2013-04-16

    A new approach for encoding DNA sequences as input for DNA sequence analysis is proposed using the error correction coding theory of communication engineering. The encoder was designed as a convolutional code model whose generator matrix is designed based on the degeneracy of codons, with a codon treated in the model as an informational unit. The utility of the proposed model was demonstrated through the analysis of twelve prokaryote and nine eukaryote DNA sequences having different GC contents. Distinct differences in code distances were observed near the initiation and termination sites in the open reading frame, which provided a well-regulated characterization of the DNA sequences. Clearly distinguished period-3 features appeared in the coding regions, and the characteristic average code distances of the analyzed sequences were approximately proportional to their GC contents, particularly in the selected prokaryotic organisms, presenting the potential utility as an added taxonomic characteristic for use in studying the relationships of living organisms.

  5. Assessing the robustness of spatial pattern sequences in a dryland vegetation model

    PubMed Central

    Chen, Yuxin; Iams, Sarah; Silber, Mary

    2016-01-01

    A particular sequence of patterns, ‘gaps→labyrinth→spots’, occurs with decreasing precipitation in previously reported numerical simulations of partial differential equation dryland vegetation models. These observations have led to the suggestion that this sequence of patterns can serve as an early indicator of desertification in some ecosystems. Because parameter values in the vegetation models can take on a range of plausible values, it is important to investigate whether the pattern sequence prediction is robust to variation. For a particular model, we find that a quantity calculated via bifurcation-theoretic analysis appears to serve as a proxy for the pattern sequences that occur in numerical simulations across a range of parameter values. We find in further analysis that the quantity takes on values consistent with the standard sequence in an ecologically relevant limit of the model parameter values. This suggests that the standard sequence is a robust prediction of the model, and we conclude by proposing a methodology for assessing the robustness of the standard sequence in other models and formulations. PMID:27118924

  6. Assessing the robustness of spatial pattern sequences in a dryland vegetation model

    NASA Astrophysics Data System (ADS)

    Gowda, Karna; Chen, Yuxin; Iams, Sarah; Silber, Mary

    2016-03-01

    A particular sequence of patterns, `gaps→labyrinth→spots', occurs with decreasing precipitation in previously reported numerical simulations of partial differential equation dryland vegetation models. These observations have led to the suggestion that this sequence of patterns can serve as an early indicator of desertification in some ecosystems. Because parameter values in the vegetation models can take on a range of plausible values, it is important to investigate whether the pattern sequence prediction is robust to variation. For a particular model, we find that a quantity calculated via bifurcation-theoretic analysis appears to serve as a proxy for the pattern sequences that occur in numerical simulations across a range of parameter values. We find in further analysis that the quantity takes on values consistent with the standard sequence in an ecologically relevant limit of the model parameter values. This suggests that the standard sequence is a robust prediction of the model, and we conclude by proposing a methodology for assessing the robustness of the standard sequence in other models and formulations.

  7. Left-lateral shear inside the North Gulf of Evia Rift, Central Greece, evidenced by relocated earthquake sequences and moment tensor inversion

    NASA Astrophysics Data System (ADS)

    Ganas, Athanassios; Mouzakiotis, Evangelos; Moshou, Alexandra; Karastathis, Vassilios

    2016-07-01

    The use of local velocity model in the analysis of seismicity recorded by the Hellenic Unified Seismological Network (HUSN), provides the opportunity to determine accurate hypocentral solutions using the weighted P- and S-wave arrival times for the November 2013, November 2014 and June 2015 North Gulf of Evia (Euboea) sequences. The hypocentral locations, including the determination of the location uncertainties, are obtained applying the non-linear probabilistic analysis. We also calculated the moment tensor solutions for the main events as well as for the strongest aftershocks. The accurate determination of seismicity showed the activation of two left-lateral, NW-SE striking, near-vertical faults, one onshore near village Taxiarchis (2013 sequence) and one offshore (offshore Malessina Peninsula, 2015 sequence). The 2014 sequence, also offshore Malessina Peninsula ruptured an oblique-slip, north-dipping normal fault with a strike of N280-290°E. All three faults occur at depths 10-16 km, with rupture zone dimensions 5-6 km along strike and 3-4 km along dip. These aftershock depths indicate a seismogenic (brittle) zone of about 15 km in depth for this rift. The left-lateral kinematics indicates strain partitioning inside the rift because of E-W horizontal compression, also evidenced by GPS data. The moderate magnitude of earthquakes (M5.2 ± 0.1) indicates that strike-slip events have a minor contribution to the crustal deformation and to active tectonics of the Gulf.

  8. A model organism for new gene discovery by cDNA sequencing

    SciTech Connect

    El-Saved, N.M.; Donelson, J.E.; Alarcon, C.M.

    1994-09-01

    One method of new gene discovery is single pass sequencing of cDNAs to identify expressed sequence tags (ESTs). Model organisms can have biological properties which makes their use advantageous over studies with humans. One such model organism with advantages for cDNA sequencing is the African trypanosome T. brucei rhodesiense. This organism has the same 40 nucleotide sequence (splice leader sequence) on the 5{prime} end of all mRNAs. We have constructed a 5{prime} cDNA library by priming off the splice leader sequence and have begun sequencing this cDNA library. To date, over nearly 500 such cDNA expressed sequence tags (ESTs) have been examined. Forty-three percent of the sequences sampled from the trypanosome cDNA library have significant similarities to sequences already in the protein and translated nucleic acid databases. Among these are cDNA sequences which encode previously reported T. brucej proteins such as the VSG, tubulin, calflagin, etc., and proteins previously identified in other trypanosomatids. Other cDNAs display significant similarities to genes in unrelated organisms encoding several ribosomal proteins, metabolic enzymes, GTP binding proteins, transcription factors, cyclophillin, nucleosomal histones, histone H1, and a macrophage stress protein, among others. The 57% of the cDNAs that are not similar to sequences currently in the databases likely encode both trypanosome-specific proteins and housekeeping proteins shared with other eukaryotes. These cDNA ESTs provide new avenues of research for exploring both the biochemistry and the genome organization of this parasite, as well as a resource for identifying the 5{prime} sequence of novel genes likely to have homology to genes expressed in other organisms.

  9. Complete mitochondrial genome sequence of the heart failure model of cardiomyopathic Syrian hamster (Mesocricetus auratus).

    PubMed

    Hu, Bo; Liu, Dong-Xing; Zhang, Yu-Qing; Song, Jian-Tao; Ji, Xian-Fei; Hou, Zhi-Qiang; Zhang, Zhen-Hai

    2016-05-01

    In this study we sequenced the complete mitochondrial genome sequencing of a heart failure model of cardiomyopathic Syrian hamster (Mesocricetus auratus) for the first time. The total length of the mitogenome was 16,267 bp. It harbored 13 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes and 1 non-coding control region.

  10. Relationship between large slip area and static stress drop of aftershocks of inland earthquake :Example of the 2007 Noto Hanto earthquake

    NASA Astrophysics Data System (ADS)

    Urano, S.; Hiramatsu, Y.; Yamada, T.

    2013-12-01

    The 2007 Noto Hanto earthquake (MJMA 6.9; hereafter referred to the main shock) occurred at 0:41(UTC) on March 25, 2007 at a depth of 11km beneath the west coast of Noto Peninsula, central Japan. The dominant slip of the main shock was on a reverse fault with a right-lateral slip and the large slip area was distributed from hypocenter to the shallow part on the fault plane (Horikawa, 2008). The aftershocks are distributed not only in the small slip area but also in the large slip area (Hiramatsu et al., 2011). In this study, we estimate static stress drops of aftershocks on the fault plane of the main shock. We discuss the relationship between the static stress drops of the aftershocks and the large slip area of the main shock by investigating spatial pattern of the values of the static stress drops. We use the waveform data obtained by the group for the joint aftershock observations of the 2007 Noto Hanto Earthquake (Sakai et al., 2007). The sampling frequency of the waveform data is 100 Hz or 200 Hz. Focusing on similar aftershocks reported by Hiramatsu et al. (2011), we analyze static stress drops by using the method of empirical Green's function (EGF) (Hough, 1997) as follows. The smallest earthquake (MJMA≥2.0) of each group of similar earthquakes is set to the EGF earthquake, and the largest earthquake (MJMA≥2.5) is set to the target earthquake. We then deconvolve the waveform of an interested earthquake with that of the EGF earthquake at each station and obtain the spectral ratio of the sources that cancels the propagation effects (path and site effects). Following the procedure of Yamada et al. (2010), we finally estimate static stress drops for P- and S-waves from corner frequencies of the spectral ratio by using a model of Madariaga (1976). The estimated average value of static stress drop is 8.2×1.3 MPa (8.6×2.2 MPa for P-wave and 7.8×1.3 MPa for S-wave). These values are coincident approximately with the static stress drop of aftershocks of other

  11. Seismic source study of the Racha-Dzhava (Georgia) earthquake from aftershocks and broad-band teleseismic body-wave records: An example of active nappe tectonics

    USGS Publications Warehouse

    Fuenzalida, H.; Rivera, L.; Haessler, H.; Legrand, D.; Philip, H.; Dorbath, L.; McCormack, D.; Arefiev, S.; Langer, C.; Cisternas, A.

    1997-01-01

    The Racha-Dzhava earthquake (Ms = 7.0) that occurred on 1991 April 29 at 09:12:48.1 GMT in the southern border of the Great Caucasus is the biggest event ever recorded in the region, stronger than the Spitak earthquake (Ms = 6.9) of 1988. A field expedition to the epicentral area was organised and a temporary seismic network of 37 stations was deployed to record the aftershock activity. A very precise image of the aftershock distribution is obtained, showing an elongated cloud oriented N105??, with one branch trending N310?? in the western part. The southernmost part extends over 80 km, with the depth ranging from 0 to 15 km, and dips north. The northern branch, which is about 30 km long, shows activity that ranges in depth from 5 to 15 km. The complex thrust dips northwards. A stress-tensor inversion from P-wave first-motion polarities shows a state of triaxial compression, with the major principal axis oriented roughly N-S, the minor principal axis being vertical. Body-waveform inversion of teleseismic seismograms was performed for the main shock, which can be divided into four subevents with a total rupture-time duration of 22 s. The most important part of the seismic moment was released by a gentle northerly dipping thrust. The model is consistent with the compressive tectonics of the region and is in agreement with the aftershock distribution and the stress tensor deduced from the aftershocks. The focal mechanisms of the three largest aftershocks were also inverted from body-wave records. The April 29th (Ms = 6.1) and May 5th (Ms = 5.4) aftershocks have thrust mechanisms on roughly E-W-oriented planes, similar to the main shock. Surprisingly, the June 15th (Ms = 6.2) aftershock shows a thrust fault striking N-S. This mechanism is explained by the structural control of the rupture along the east-dipping geometry of the Dzirula Massif close to the Borzhomi-Kazbeg strike-slip fault. In fact, the orientation and shape of the stress tensor produce a thrust on a N

  12. The use of synthetic input sequences in time series modeling

    NASA Astrophysics Data System (ADS)

    de Oliveira, Dair José; Letellier, Christophe; Gomes, Murilo E. D.; Aguirre, Luis A.

    2008-08-01

    In many situations time series models obtained from noise-like data settle to trivial solutions under iteration. This Letter proposes a way of producing a synthetic (dummy) input, that is included to prevent the model from settling down to a trivial solution, while maintaining features of the original signal. Simulated benchmark models and a real time series of RR intervals from an ECG are used to illustrate the procedure.

  13. SEQAID: a DNA sequence assembling program based on a mathematical model.

    PubMed Central

    Peltola, H; Söderlund, H; Ukkonen, E

    1984-01-01

    A program package, called SEQAID, to support DNA sequencing is presented. The program automatically assembles long DNA sequences from short fragments with minimal user interaction. Various tools for controlling the assembling process are also available. The main novel features of the system are that SEQAID implements several new well-behaved algorithms based on a mathematical model of the problem. It also utilizes available information on restriction fragments to detect illegitimate overlaps and to find relationships between separately assembled sequence blocks. Experiences with the system are reported including an extremely pathological real sequence which offers an interesting benchmark for this kind of programs. PMID:6320092

  14. Elastic Waves: Mental Models and Teaching/Learning Sequences

    NASA Astrophysics Data System (ADS)

    Tarantino, Giovanni

    In last years many research studies have pointed out relevant student diff- culties in understanding the physics of mechanical waves. Moreover, it has been reported that these diffculties deal with some fundamental concepts as the role of the medium in wave propagation, the superposition principle and the mathematical description of waves involving the use of functions of two variables. In the context of pre-service courses for teacher preparation a teaching/learning (T/L) sequence based on using simple RTL experiments and interactive simulation environments aimed to show the effect of medium properties on the propagation speed of a wave pulse, has been experimented. Here, preliminary results of investigations carried out with a 120 traineeteacher (TT) group are reported and discussed.

  15. Modeling sustainable groundwater management: packaging and sequencing of policy interventions.

    PubMed

    Esteban, Encarna; Dinar, Ariel

    2013-04-15

    Of the many studies estimating effectiveness of policy reforms most have been considering various types of policy reforms in isolation from each other. Such pattern has also been the case in water resource regulations. In the case of groundwater almost all policy interventions considered in the literature have been implemented individually, without taking into account the possible interactions and impacts among them. In this paper, we focus on two policy instruments: water quota and uniform water tax. The paper demonstrates how packaging and sequencing sets of policy interventions, with possible triggers to initiate their time of implementation, may be more effective in achieving a sustainable groundwater management than single policies when environmental externalities exist. The policy instruments are applied to the Western la Mancha aquifer in Southeast Spain, a major aquifer that is managed by a command and control approach.

  16. On the c-values of the off-fault aftershocks triggered by the 1995 Kobe earthquake, Japan

    NASA Astrophysics Data System (ADS)

    Sugaya, K.; Hiramatsu, Y.; Furumoto, M.; Katao, H.; Ogata, Y.

    2010-12-01

    The Omori-Utsu law is applicable not only to aftershocks in a source region but also to off-fault aftershocks triggered by the mainshock.In this study, we estimate the c-values using the maximum-likelihood method (Ogata, 1983) from the seismicity activation in the Tamba region induced by the coseismic static stress change due to the 1995 Kobe earthquake of M7.3, Japan. We use earthquakes (M≥1.8) shallower than 20 km from the JMA catalog and remove remarked clusters of the aftershock due to moderate earthquakes with the method of Reasenberg (1985). Our analyzed period is from the occurrence of the earthquake (17 January 1995) to December 1995. The obtained c-values in the divided subregions, near and far to the rupture zone, are 58.1 ± 26.1 days and 164.7 ± 98.0 days, respectively. This is consistent with the rate- and state-dependent friction law of Dieterich (1994) in that the c-values of induced off-fault seismicity are larger than those of the source region depending on the static stress change. We estimate Aσ and the stressing rate after the earthquake in the whole region with the average ΔCFS of 30 kPa (Hashimoto, 1995, 1997) using a grid search following Toda et al. (2005). The friction law’s parameters in the whole region are estimated to be 13.8 ~ 16.2 kPa/yr and 15.0 ~ 16.6 kPa at the stressing rate and Aσ, respectively. Furthermore, we estimate ΔCFSs in the two subregions using the stressing rate of 15.5 kPa/yr and Aσ of 15.5 kPa obtained above. The obtained ΔCFSs in the divided subregions, near and far to the rupture zone, are 39.9 ~ 43.4 kPa and 17.3 ~ 19.9 kPa, respectively. These are coincident with the distribution of ΔCFS drawn by using a geodetic fault model (Hashimoto et al., 1996).

  17. Modeling financial markets by the multiplicative sequence of trades

    NASA Astrophysics Data System (ADS)

    Gontis, V.; Kaulakys, B.

    2004-12-01

    We introduce the stochastic multiplicative point process modeling trading activity of financial markets. Such a model system exhibits power-law spectral density S(f)∝1/fβ, scaled as power of frequency for various values of β between 0.5 and 2. Furthermore, we analyze the relation between the power-law autocorrelations and the origin of the power-law probability distribution of the trading activity. The model reproduces the spectral properties of trading activity and explains the mechanism of power-law distribution in real markets.

  18. Spin models inferred from patient-derived viral sequence data faithfully describe HIV fitness landscapes

    NASA Astrophysics Data System (ADS)

    Shekhar, Karthik; Ruberman, Claire F.; Ferguson, Andrew L.; Barton, John P.; Kardar, Mehran; Chakraborty, Arup K.

    2013-12-01

    Mutational escape from vaccine-induced immune responses has thwarted the development of a successful vaccine against AIDS, whose causative agent is HIV, a highly mutable virus. Knowing the virus' fitness as a function of its proteomic sequence can enable rational design of potent vaccines, as this information can focus vaccine-induced immune responses to target mutational vulnerabilities of the virus. Spin models have been proposed as a means to infer intrinsic fitness landscapes of HIV proteins from patient-derived viral protein sequences. These sequences are the product of nonequilibrium viral evolution driven by patient-specific immune responses and are subject to phylogenetic constraints. How can such sequence data allow inference of intrinsic fitness landscapes? We combined computer simulations and variational theory á la Feynman to show that, in most circumstances, spin models inferred from patient-derived viral sequences reflect the correct rank order of the fitness of mutant viral strains. Our findings are relevant for diverse viruses.

  19. Exploiting mid-range DNA patterns for sequence classification: binary abstraction Markov models

    PubMed Central

    Shepard, Samuel S.; McSweeny, Andrew; Serpen, Gursel; Fedorov, Alexei

    2012-01-01

    Messenger RNA sequences possess specific nucleotide patterns distinguishing them from non-coding genomic sequences. In this study, we explore the utilization of modified Markov models to analyze sequences up to 44 bp, far beyond the 8-bp limit of conventional Markov models, for exon/intron discrimination. In order to analyze nucleotide sequences of this length, their information content is first reduced by conversion into shorter binary patterns via the application of numerous abstraction schemes. After the conversion of genomic sequences to binary strings, homogenous Markov models trained on the binary sequences are used to discriminate between exons and introns. We term this approach the Binary Abstraction Markov Model (BAMM). High-quality abstraction schemes for exon/intron discrimination are selected using optimization algorithms on supercomputers. The best MM classifiers are then combined using support vector machines into a single classifier. With this approach, over 95% classification accuracy is achieved without taking reading frame into account. With further development, the BAMM approach can be applied to sequences lacking the genetic code such as ncRNAs and 5′-untranslated regions. PMID:22344692

  20. Systematic Detections of Early Aftershocks and Remotely Triggered Seismicity in China Following the 2015 Mw7.8 Gorkha, Nepal earthquake

    NASA Astrophysics Data System (ADS)

    Wu, J.; Peng, Z.; Yao, D.; LI, L.; Meng, X.; Wang, B.; Wang, W.; Li, C.

    2015-12-01

    some time delays). The early aftershocks show systematic along-strike migrations, similar to other recently studied aftershock sequences. Our next step is to extend the same analysis to longer time period before and after the mainshock to detect potential foreshocks and investigate longer-time evolutions of seismicity in Nepal.

  1. Suite of tools for statistical N-gram language modeling for pattern mining in whole genome sequences.

    PubMed

    Ganapathiraju, Madhavi K; Mitchell, Asia D; Thahir, Mohamed; Motwani, Kamiya; Ananthasubramanian, Seshan

    2012-12-01

    Genome sequences contain a number of patterns that have biomedical significance. Repetitive sequences of various kinds are a primary component of most of the genomic sequence patterns. We extended the suffix-array based Biological Language Modeling Toolkit to compute n-gram frequencies as well as n-gram language-model based perplexity in windows over the whole genome sequence to find biologically relevant patterns. We present the suite of tools and their application for analysis on whole human genome sequence.

  2. On species sampling sequences induced by residual allocation models

    PubMed Central

    Rodríguez, Abel; Quintana, Fernando A.

    2014-01-01

    We discuss fully Bayesian inference in a class of species sampling models that are induced by residual allocation (sometimes called stick-breaking) priors on almost surely discrete random measures. This class provides a generalization of the well-known Ewens sampling formula that allows for additional flexibility while retaining computational tractability. In particular, the procedure is used to derive the exchangeable predictive probability functions associated with the generalized Dirichlet process of Hjort (2000) and the probit stick-breaking prior of Chung and Dunson (2009) and Rodriguez and Dunson (2011). The procedure is illustrated with applications to genetics and nonparametric mixture modeling. PMID:25477705

  3. Spatial variation of the aftershock activity across the Kachchh Rift Basin and its seismotectonic implications

    NASA Astrophysics Data System (ADS)

    Singh, A. P.; Mishra, O. P.; Kumar, Dinesh; Kumar, Santosh; Yadav, R. B. S.

    2012-04-01

    We analyzed 3365 relocated aftershocks with magnitude of completeness ( Mc) ≥1.7 that occurred in the Kachchh Rift Basin (KRB) between August 2006 and December 2010. The analysis of the new aftershock catalogue has led to improved understanding of the subsurface structure and of the aftershock behaviour. We characterized aftershock behaviour in terms of a-value, b-value, spatial fractal dimension ( D s ), and slip ratio (ratio of the slip that occurred on the primary fault and that of the total slip). The estimated b-value is 1.05, which indicates that the earthquake occurred due to active tectonics in the region. The three dimensional b-value mapping shows that a high b-value region is sandwiched around the 2001 Bhuj mainshock hypocenter at depths of 20-25 km between two low b-value zones above and below this depth range. The D s -value was estimated from the double-logarithmic plot of the correlation integral and distance between hypocenters, and is found to be 2.64 ± 0.01, which indicates random spatial distribution beneath the source zone in a two-dimensional plane associated with fluid-filled fractures. A slip ratio of about 0.23 reveals that more slip occurred on secondary fault systems in and around the 2001 Bhuj earhquake ( Mw 7.6) source zone in KRB.

  4. Aftershock seismicity and Tectonic Setting of the 16 September 2015 Mw 8.3 Illapel earthquake

    NASA Astrophysics Data System (ADS)

    Lange, Dietrich; Geersen, Jacob; Barrientos, Sergio; Moreno, Marcos; Grevemeyer, Ingo; Contreras-Reyes, Eduardo; Kopp, Heidrun

    2016-04-01

    Powerful subduction zone earthquakes rupture thousands of square kilometers along continental margins but at certain locations earthquake rupture terminates. On 16 September 2015 the Mw. 8.3 Illapel earthquake ruptured a 200 km long stretch of the Central Chilean subduction zone, triggering a tsunami and causing significant damage. Here we analyze the spatial pattern of coseismic rupture and the temporal and spatial pattern of local seismicity for aftershocks and foreshocks in relation to the tectonic setting in the earthquake area. Aftershock seismicity surrounds the rupture area in lateral and downdip direction. For the first 24 hours following the mainshock we observe aftershock migration to both lateral directions with velocities of approximately 2.5 and 5 km/h. At the southern earthquake boundary aftershocks cluster around individual subducted seamounts located on the prolongation of the downthrusting Juan Fernández Ridge indicating stress transfer from the main rupture area. In the northern part of the rupture area a deeper band of local seismicity is observed indicating an alternation of seismic to aseismic behavior of the plate interface in downdip direction. This aseismic region at ~30 km depth that is also observed before the Illapel 2015 earthquake is likely controlled by the intersection of the continental Moho with the subducting slab.

  5. Aftershock source mechanisms from the June 9, 1994, Deep Bolivian Earthquake

    NASA Astrophysics Data System (ADS)

    Tinker, Mark Andrew; Wallace, Terry C.; Beck, Susan L.; Silver, Paul G.; Zandt, George

    The Mw 8.3 Bolivia earthquake occurred on June 9, 1994, at a depth of 636 km. This is the largest deep event in recorded history and ruptured a portion of the down-going Nazca slab unknown to have ruptured previously. We recorded the main shock and aftershocks on the BANJO and SEDA portable, broadband seismic arrays deployed in Bolivia during this event. Myers et al. (this issue) identified and located 36 aftershocks (M>2) for the 10-day period following the main shock. We use a grid search technique to determine focal mechanisms for 12 of these aftershocks ranging in magnitude from 2.7 to 5.3. We compare the observed P to SV and SH ratios to a series of synthetics that represent different fault plane orientations. We find consistent focal mechanisms with the T-axis roughly horizontal and oriented approximately east-west, and the P-axis predominantly vertical. The aftershock focal mechanisms indicate a rotation of the P-axis within the slab from down-dip compression prior to the main shock to a near-vertical direction afterwards. This observation is consistent with the release of shear stress on the near-horizontal rupture plane and the subsequent rotation of the maximum compressive stress to a fault -normal orientation.

  6. Modeling transformations of neurodevelopmental sequences across mammalian species.

    PubMed

    Workman, Alan D; Charvet, Christine J; Clancy, Barbara; Darlington, Richard B; Finlay, Barbara L

    2013-04-24

    A general model of neural development is derived to fit 18 mammalian species, including humans, macaques, several rodent species, and six metatherian (marsupial) mammals. The goal of this work is to describe heterochronic changes in brain evolution within its basic developmental allometry, and provide an empirical basis to recognize equivalent maturational states across animals. The empirical data generating the model comprises 271 developmental events, including measures of initial neurogenesis, axon extension, establishment, and refinement of connectivity, as well as later events such as myelin formation, growth of brain volume, and early behavioral milestones, to the third year of human postnatal life. The progress of neural events across species is sufficiently predictable that a single model can be used to predict the timing of all events in all species, with a correlation of modeled values to empirical data of 0.9929. Each species' rate of progress through the event scale, described by a regression equation predicting duration of development in days, is highly correlated with adult brain size. Neural heterochrony can be seen in selective delay of retinogenesis in the cat, associated with greater numbers of rods in its retina, and delay of corticogenesis in all species but rodents and the rabbit, associated with relatively larger cortices in species with delay. Unexpectedly, precocial mammals (those unusually mature at birth) delay the onset of first neurogenesis but then progress rapidly through remaining developmental events.

  7. Modeling Transformations of Neurodevelopmental Sequences across Mammalian Species

    PubMed Central

    Workman, Alan D.; Charvet, Christine J.; Clancy, Barbara; Darlington, Richard B.

    2013-01-01

    A general model of neural development is derived to fit 18 mammalian species, including humans, macaques, several rodent species, and six metatherian (marsupial) mammals. The goal of this work is to describe heterochronic changes in brain evolution within its basic developmental allometry, and provide an empirical basis to recognize equivalent maturational states across animals. The empirical data generating the model comprises 271 developmental events, including measures of initial neurogenesis, axon extension, establishment, and refinement of connectivity, as well as later events such as myelin formation, growth of brain volume, and early behavioral milestones, to the third year of human postnatal life. The progress of neural events across species is sufficiently predictable that a single model can be used to predict the timing of all events in all species, with a correlation of modeled values to empirical data of 0.9929. Each species' rate of progress through the event scale, described by a regression equation predicting duration of development in days, is highly correlated with adult brain size. Neural heterochrony can be seen in selective delay of retinogenesis in the cat, associated with greater numbers of rods in its retina, and delay of corticogenesis in all species but rodents and the rabbit, associated with relatively larger cortices in species with delay. Unexpectedly, precocial mammals (those unusually mature at birth) delay the onset of first neurogenesis but then progress rapidly through remaining developmental events. PMID:23616543

  8. An efficient binomial model-based measure for sequence comparison and its application.

    PubMed

    Liu, Xiaoqing; Dai, Qi; Li, Lihua; He, Zerong

    2011-04-01

    Sequence comparison is one of the major tasks in bioinformatics, which could serve as evidence of structural and functional conservation, as well as of evolutionary relations. There are several similarity/dissimilarity measures for sequence comparison, but challenges remains. This paper presented a binomial model-based measure to analyze biological sequences. With help of a random indicator, the occurrence of a word at any position of sequence can be regarded as a random Bernoulli variable, and the distribution of a sum of the word occurrence is well known to be a binomial one. By using a recursive formula, we computed the binomial probability of the word count and proposed a binomial model-based measure based on the relative entropy. The proposed measure was tested by extensive experiments including classification of HEV genotypes and phylogenetic analysis, and further compared with alignment-based and alignment-free measures. The results demonstrate that the proposed measure based on binomial model is more efficient.

  9. Near-trench aftershocks of the 2011 Tohoku-oki earthquake based on ocean bottom seismograph obserbations

    NASA Astrophysics Data System (ADS)

    Obana, K.; Shinohara, M.; Yamada, T.; Uehira, K.; Hino, R.; Shiobara, H.; Nakahigashi, K.; Sugioka, H.; Ito, A.; Nakamura, Y.; No, T.; Miura, S.; Kodaira, S.; Takahashi, N.

    2012-12-01

    After the 2011 Mw 9.0 Tohoku-Oki Earthquakes, aftershocks with a normal-faulting focal mechanism have been activated both in the overriding plate and incoming/subducting Pacific plate near the trench axis [e.g., Asano et al., 2011]. We conducted ocean bottom seismograph (OBS) observations using short-period and broad-band OBSs near the Japan Trench from August to October 2011. These OBSs were deployed on the landward slope including the area, where the several tens of meters co-seismic displacement was observed [e.g., Fujiwara et al., 2011], with approximately 10 to 20 km separation in horizontal. Earthquakes were detected from continuous seismograms obtained by the OBSs. The phase arrival times were picked manually. We determined the hypocenters by using a grid search method in a 2-D velocity model based on the active seismic survey [Ito et al., 2005]. Focal mechanisms were also estimated from polarities of the first motion of P-wave arrivals. The obtained results show that normal-faulting earthquakes occurred within the overriding plate. These earthquakes likely relate to the normal fault system in the overriding plate. On the other hand, no earthquakes have been observed within the toe of the overriding plate, where the several tens of meters of co-seismic slip displacement along the plate interface occurred during the 2011 Tohoku-oki Earthquake. Earthquakes located within the subducting plate have a strike-slip faulting focal mechanism. These earthquakes are considered to be an aftershock activity of the Mw 7.0 strike slip event occurred on July 10, 2011.

  10. Reflection imaging using RVSP processing of aftershock recordings from the August 23, 2011 central Virginia earthquake

    NASA Astrophysics Data System (ADS)

    Quiros, D. A.; Brown, L. D.; Davenport, K.; Han, L.; Hole, J. A.; Chapman, M. C.; Mooney, W. D.; Cabolova, A.

    2012-12-01

    On August 23, 2011, a magnitude Mw 5.6 earthquake occurred in central Virginia and was felt over much of the eastern United States. This event, which had a NE-striking reverse faulting focal mechanism at a hypocentral depth of 6 km, occurred in the previously recognized "Central Virginia Seismic Zone". The likelihood of numerous small and several moderate-sized aftershocks motivated the rapid post-seismic deployment of a high-density seismic array by a team of scientists from Cornell University, Virginia Tech and the U.S. Geological Survey (USGS). Traditional earthquake aftershock deployments consist of a few tens of instruments at nominal distances that are in the order of kilometers. The Aftershock Imaging with Dense Arrays (AIDA) experiment in Virginia represents a prototype effort to field a deployment with hundreds of seismographs at sub-kilometer spacing (Δx ~ 200 m) using technology currently available (Reftek RT125A) from the EarthScope Flexible Array. One of the major expectations associated with such dense arrays was the potential for high resolution imaging of the hypocentral region using direct (refracted) and reflected seismic waves from the aftershock sources. Here we report our efforts to image reflective structures using techniques associated with Vertical Seismic Profiling (VSP). VSP is usually associated with recording of surface sources by instruments deployed down a borehole seismic survey or surface recording of sources within the borehole (Reverse VSP). The geometry of VSP surveys (i.e. reverse or regular) often provides better resolution than conventional surface seismic surveys because of the shorter ray paths involved (thus less attenuation) as well more definitive ties to geology encountered in the borehole. The aftershocks of the VA event can be treated as sources in a reverse VSP geometry since they span a range of depths in a relatively small area. We have imaged structure in the hypocentral region by applying VSP processing algorithms

  11. Estimation of the parameters of ETAS models by Simulated Annealing.

    PubMed

    Lombardi, Anna Maria

    2015-02-12

    This paper proposes a new algorithm to estimate the maximum likelihood parameters of an Epidemic Type Aftershock Sequences (ETAS) model. It is based on Simulated Annealing, a versatile method that solves problems of global optimization and ensures convergence to a global optimum. The procedure is tested on both simulated and real catalogs. The main conclusion is that the method performs poorly as the size of the catalog decreases because the effect of the correlation of the ETAS parameters is more significant. These results give new insights into the ETAS model and the efficiency of the maximum-likelihood method within this context.

  12. Estimation of the parameters of ETAS models by Simulated Annealing

    NASA Astrophysics Data System (ADS)

    Lombardi, Anna Maria

    2015-02-01

    This paper proposes a new algorithm to estimate the maximum likelihood parameters of an Epidemic Type Aftershock Sequences (ETAS) model. It is based on Simulated Annealing, a versatile method that solves problems of global optimization and ensures convergence to a global optimum. The procedure is tested on both simulated and real catalogs. The main conclusion is that the method performs poorly as the size of the catalog decreases because the effect of the correlation of the ETAS parameters is more significant. These results give new insights into the ETAS model and the efficiency of the maximum-likelihood method within this context.

  13. Estimation of the parameters of ETAS models by Simulated Annealing

    PubMed Central

    Lombardi, Anna Maria

    2015-01-01

    This paper proposes a new algorithm to estimate the maximum likelihood parameters of an Epidemic Type Aftershock Sequences (ETAS) model. It is based on Simulated Annealing, a versatile method that solves problems of global optimization and ensures convergence to a global optimum. The procedure is tested on both simulated and real catalogs. The main conclusion is that the method performs poorly as the size of the catalog decreases because the effect of the correlation of the ETAS parameters is more significant. These results give new insights into the ETAS model and the efficiency of the maximum-likelihood method within this context. PMID:25673036

  14. Reactive Secondary Sequence Oxidative Pathology Polymer Model and Antioxidant Tests

    PubMed Central

    Petersen, Richard C.

    2014-01-01

    Aims To provide common Organic Chemistry/Polymer Science thermoset free-radical crosslinking Sciences for Medical understanding and also present research findings for several common vitamins/antioxidants with a new class of drugs known as free-radical inhibitors. Study Design Peroxide/Fenton transition-metal redox couples that generate free radicals were combined with unsaturated lipid oils to demonstrate thermoset-polymer chain growth by crosslinking with the α-β-unsaturated aldehyde acrolein into rubbery/adhesive solids. Further, Vitamin A and beta carotene were similarly studied for crosslink pathological potential. Also, free-radical inhibitor hydroquinone was compared for antioxidant capability with Vitamin E. Place and Duration of Study Department of Materials Science and Engineering and Department of Biomaterials, University of Alabama at Birmingham, between June 2005 and August 2012. Methodology Observations were recorded for Fenton free-radical crosslinking of unsaturated lipids and vitamin A/beta carotene by photography further with weight measurements and percent-shrinkage testing directly related to covalent crosslinking of unsaturated lipids recorded over time with different concentrations of acrolein. Also, hydroquinone and vitamin E were compared at concentrations from 0.0–7.3wt% as antioxidants for reductions in percent-shrinkage measurements, n = 5. Results Unsaturated lipid oils responded to Fenton thermoset-polymer reactive secondary sequence reactions only by acrolein with crosslinking into rubbery-type solids and different non-solid gluey products. Further, molecular oxygen crosslinking was demonstrated with lipid peroxidation and acrolein at specially identified margins. By peroxide/Fenton free-radical testing, both vitamin A and beta-carotene demonstrated possible pathology chemistry for chain-growth crosslinking. During lipid/acrolein testing over a 50 hour time period at 7.3wt% antioxidants, hydroquinone significantly reduced percent

  15. Detailed analysis of the spatio-temporal evolution of tremor, foreshock, and aftershock activities near the September 5, 2012 Nicoya Peninsula earthquake

    NASA Astrophysics Data System (ADS)

    Walter, J. I.; Peng, Z.; Schwartz, S. Y.; Meng, X.; Newman, A. V.; Protti, M.

    2013-05-01

    The subduction megathrust interface, at the Nicoya Peninsula, exhibits a wide range of complex fault behavior, from recently discovered slow slip and tremor, numerous microearthquakes, to infrequent megathrust (> Mw 7) earthquakes. In contrast to other subduction zones, the Nicoya tremor originates up-dip, down-dip, and within the seismogenic zone. The September 5, 2012 earthquake makes the Nicoya Peninsula uniquely poised to investigate the wide range of fault behavior and spatio-temporal evolution of seismic activity around the mainshock, as the seismogenic zone lies directly below the Peninsula. Preliminary matched-filter analysis using a template earthquake that precedes the mainshock by ~120 s indicates similar events occurring 20-40 min prior to the mainshock, as well as, immediately following the mainshock. We are expanding this analysis with a broader catalogue of template events and utilizing matched-filter codes optimized for graphics processing units (GPUs). While detailed analysis of the foreshock/aftershock sequence is ongoing, the early aftershocks cluster in a distinct region that is immediately adjacent to regions that have undergone slow slip in past events. We hope to gain better insight into the spatio-temporal transitions from stable sliding to stick-slip motion, and underlying physics of earthquake nucleation and interaction.

  16. Exploiting Non-sequence Data in Dynamic Model Learning

    DTIC Science & Technology

    2013-10-01

    dynamic process of interest. For example, the Sloan Digital Sky Survey (SDSS)1 has collected images of millions of celestial objects, each of which may...function of Z and hence Z. Since we assume the true dynamics to be smooth, a natural way to reconstruct a temporal ordering would be to solve the...program (3.42) better captures the dynamic nature of the data. • The initial models learnt from ordered cluster centers already perform quite well

  17. Adapting Pipeline Architectures to Track Developing Aftershock Sequences and Recurrent Explosions (Postprint)

    DTIC Science & Technology

    2012-05-08

    Proceedings of the 2011 Monitoring Research Review – Ground-Based Nuclear Explosion Monitoring Technologies, 13 – 15 September 2011, Tucson , AZ, Volume I, pp...as the 2004 Sumatra-Andaman Islands earthquake, the 2008 Sichuan earthquake, and the 2011 Japan earthquake flood seismic networks with thousands of

  18. Adapting Pipeline Architectures to Track Developing Aftershock Sequences and Recurrent Explosions

    DTIC Science & Technology

    2014-02-14

    unlimited. x APPENDIX – List of Figures Fig. A.1 Events from the bulletins of the International Seismological Center (www.isc.ac.uk, left) and the...in seismology . Whereas a correlator compares the temporal pattern of a signal from one event with the temporal pattern of signal from a subsequent...ISBN-13: 978-0801854149 Harris, D. (1991) “A waveform correlation method for identifying quarry explosions” Bulletin of the Seismological Society

  19. The PISA Pre-Main Sequence accreting models

    NASA Astrophysics Data System (ADS)

    Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla

    2013-07-01

    The poster investigates the effect of accretion processes on the evolution of stellar models computed by means of the well tested and updated PROSECCO evolutionary code, under the hypothesis of thin-disk accretion. We analysed the effect on the evolution of the adoption of different parameters as the accretion rate, accretion history, seed mass, and the fraction of the infalling matter energy (alpha_acc) deposed in to the star (accretion energy). We confirm that the most critical parameter is the accretion energy. We show that, depending on alpha_acc the evolution of accreting and non-accreting objects can be completely different, confirming that the adoption of small alpha_acc value (i.e. small accretion energy, cold accretion) produces fainter and more compact models with respect to the ones predicted from non-accreting structures at the same mass and age, models that can not be reconciled with the data available for young objects (i.e. position in the HR diagram, lithium abundances). On the contrary, if a large part of the accretion luminosity is deposed into the star (alpha_acc = 1, hot accretion), at least during the fisrt stages of the accretion phase or during bursts episodes, large radii and luminosities are achievable, with resulting structures much more similar to the non-accreting ones.

  20. Using the Gauss-Newton Method to Invert for Brune Model Moment, Corner Frequency, and Kappa Parameters: Results from the Canterbury, New Zealand Earthquake Sequence

    NASA Astrophysics Data System (ADS)

    Neighbors, C.; Cochran, E. S.; Ryan, K. J.; Kaiser, A. E.

    2015-12-01

    The seismic spectrum can be modeled by assuming a Brune spectrum and estimating the parameters of seismic moment (M0), corner frequency (fc), and the high frequency site attenuation (κ). Traditionally studies either hold fixed or use a predefined set of trial values for one of the parameters (e.g., fc) and then solve for the remaining parameters. Here, we use the Gauss-Newton nonlinear least-squares method to simultaneously determine the M0, fc, and high-frequency κ for each event-station pair. We use data collected during the Canterbury, New Zealand earthquake sequence. The seismic stations include the permanent GeoNet accelerometer network as well as a dense network of nearly 200 Quake-Catcher Network (QCN) MEMs accelerometers installed following the 3 September 2010 M 7.1 Darfield earthquake. We examine over 180 aftershocks ≥ Mw3.5 that occurred from 9 September 2010 to 31 July 2011 and are captured by both networks. We use Fourier-transformed S-wave windows that include 80% of the S-wave energy and fit the acceleration spectra between 0.5 and 20 Hz. We apply a path and site correction to the data as described in Oth and Kaiser (2014). Then, the records are smoothed using a Konno and Omachi (1998) filter and uniformly resampled in log space. Initial "best guesses" for M0 and fc are determined from GNS catalog magnitudes and by assuming a 100 bar (10 MPa) stress drop and an initial κ is determined from an automated high-frequency fit method. We use a parametric inversion technique that requires a single M0 and fc for each event, while κ is allowed to vary by station to reflect varying site conditions. Final solutions for M0, fc, and κ are iteratively calculated by minimizing the residual function. After Brune (1970, 1971), the stress drop is determined from the best-fit fc. Moment magnitudes determined agree well with the GNS catalog, with a median difference of 0.12 Mw and 0.20 Mw for GeoNet and QCN inversions, respectively. Stress drop results are within

  1. Combining next-generation sequencing and online databases for microsatellite development in non-model organisms

    PubMed Central

    Rico, Ciro; Normandeau, Eric; Dion-Côté, Anne-Marie; Rico, María Inés; Côté, Guillaume; Bernatchez, Louis

    2013-01-01

    Next-generation sequencing (NGS) is revolutionising marker development and the rapidly increasing amount of transcriptomes published across a wide variety of taxa is providing valuable sequence databases for the identification of genetic markers without the need to generate new sequences. Microsatellites are still the most important source of polymorphic markers in ecology and evolution. Motivated by our long-term interest in the adaptive radiation of a non-model species complex of whitefishes (Coregonus spp.), in this study, we focus on microsatellite characterisation and multiplex optimisation using transcriptome sequences generated by Illumina® and Roche-454, as well as online databases of Expressed Sequence Tags (EST) for the study of whitefish evolution and demographic history. We identified and optimised 40 polymorphic loci in multiplex PCR reactions and validated the robustness of our analyses by testing several population genetics and phylogeographic predictions using 494 fish from five lakes and 2 distinct ecotypes. PMID:24296905

  2. Conserved intergenic sequences revealed by CTAG-profiling in Salmonella: thermodynamic modeling for function prediction

    PubMed Central

    Tang, Le; Zhu, Songling; Mastriani, Emilio; Fang, Xin; Zhou, Yu-Jie; Li, Yong-Guo; Johnston, Randal N.; Guo, Zheng; Liu, Gui-Rong; Liu, Shu-Lin

    2017-01-01

    Highly conserved short sequences help identify functional genomic regions and facilitate genomic annotation. We used Salmonella as the model to search the genome for evolutionarily conserved regions and focused on the tetranucleotide sequence CTAG for its potentially important functions. In Salmonella, CTAG is highly conserved across the lineages and large numbers of CTAG-containing short sequences fall in intergenic regions, strongly indicating their biological importance. Computer modeling demonstrated stable stem-loop structures in some of the CTAG-containing intergenic regions, and substitution of a nucleotide of the CTAG sequence would radically rearrange the free energy and disrupt the structure. The postulated degeneration of CTAG takes distinct patterns among Salmonella lineages and provides novel information about genomic divergence and evolution of these bacterial pathogens. Comparison of the vertically and horizontally transmitted genomic segments showed different CTAG distribution landscapes, with the genome amelioration process to remove CTAG taking place inward from both terminals of the horizontally acquired segment. PMID:28262684

  3. Conserved intergenic sequences revealed by CTAG-profiling in Salmonella: thermodynamic modeling for function prediction

    NASA Astrophysics Data System (ADS)

    Tang, Le; Zhu, Songling; Mastriani, Emilio; Fang, Xin; Zhou, Yu-Jie; Li, Yong-Guo; Johnston, Randal N.; Guo, Zheng; Liu, Gui-Rong; Liu, Shu-Lin

    2017-03-01

    Highly conserved short sequences help identify functional genomic regions and facilitate genomic annotation. We used Salmonella as the model to search the genome for evolutionarily conserved regions and focused on the tetranucleotide sequence CTAG for its potentially important functions. In Salmonella, CTAG is highly conserved across the lineages and large numbers of CTAG-containing short sequences fall in intergenic regions, strongly indicating their biological importance. Computer modeling demonstrated stable stem-loop structures in some of the CTAG-containing intergenic regions, and substitution of a nucleotide of the CTAG sequence would radically rearrange the free energy and disrupt the structure. The postulated degeneration of CTAG takes distinct patterns among Salmonella lineages and provides novel information about genomic divergence and evolution of these bacterial pathogens. Comparison of the vertically and horizontally transmitted genomic segments showed different CTAG distribution landscapes, with the genome amelioration process to remove CTAG taking place inward from both terminals of the horizontally acquired segment.

  4. Conserved intergenic sequences revealed by CTAG-profiling in Salmonella: thermodynamic modeling for function prediction.

    PubMed

    Tang, Le; Zhu, Songling; Mastriani, Emilio; Fang, Xin; Zhou, Yu-Jie; Li, Yong-Guo; Johnston, Randal N; Guo, Zheng; Liu, Gui-Rong; Liu, Shu-Lin

    2017-03-06

    Highly conserved short sequences help identify functional genomic regions and facilitate genomic annotation. We used Salmonella as the model to search the genome for evolutionarily conserved regions and focused on the tetranucleotide sequence CTAG for its potentially important functions. In Salmonella, CTAG is highly conserved across the lineages and large numbers of CTAG-containing short sequences fall in intergenic regions, strongly indicating their biological importance. Computer modeling demonstrated stable stem-loop structures in some of the CTAG-containing intergenic regions, and substitution of a nucleotide of the CTAG sequence would radically rearrange the free energy and disrupt the structure. The postulated degeneration of CTAG takes distinct patterns among Salmonella lineages and provides novel information about genomic divergence and evolution of these bacterial pathogens. Comparison of the vertically and horizontally transmitted genomic segments showed different CTAG distribution landscapes, with the genome amelioration process to remove CTAG taking place inward from both terminals of the horizontally acquired segment.

  5. Polypeptoids: A model system for exploring sequence and shape effects on block copolymer self-assembly

    NASA Astrophysics Data System (ADS)

    Segalman, Rachel

    2015-03-01

    While our ability to understand the detailed relationship between block copolymer chemistry and mesoscopic self-assembly has made remarkable progress over the last many years, yet we are still limited to a relatively small number of blocks in terms of structure-property understanding. Thus, there is a need to explore self-assembly phase space with sequence using a model system. Polypeptoids are non-natural, sequence specific polymers that offer the opportunity to probe the effect of sequence on self-assembly with much simpler molecular interactions and more scalable synthesis than traditional polypeptides. In this talk, I will discuss the use of this model system to understand the role of sequence on chain collapse and globule formation in solution, polymer crystallization, and block copolymer self-assembly. I will then discuss potential application as surface active agents for anti-fouling.

  6. Transgenerational inheritance: Models and mechanisms of non-DNA sequence-based inheritance.

    PubMed

    Miska, Eric A; Ferguson-Smith, Anne C

    2016-10-07

    Heritability has traditionally been thought to be a characteristic feature of the genetic material of an organism-notably, its DNA. However, it is now clear that inheritance not based on DNA sequence exists in multiple organisms, with examples found in microbes, plants, and invertebrate and vertebrate animals. In mammals, the molecular mechanisms have been challenging to elucidate, in part due to difficulties in designing robust models and approaches. Here we review some of the evidence, concepts, and potential mechanisms of non-DNA sequence-based transgenerational inheritance. We highlight model systems and discuss whether phenotypes are replicated or reconstructed over successive generations, as well as whether mechanisms operate at transcriptional and/or posttranscriptional levels. Finally, we explore the short- and long-term implications of non-DNA sequence-based inheritance. Understanding the effects of non-DNA sequence-based mechanisms is key to a full appreciation of heritability in health and disease.

  7. Next Generation Sequencing Technologies: The Doorway to the Unexplored Genomics of Non-Model Plants

    PubMed Central

    Unamba, Chibuikem I. N.; Nag, Akshay; Sharma, Ram K.

    2015-01-01

    Non-model plants i.e., the species which have one or all of the characters such as long life cycle, difficulty to grow in the laboratory or poor fecundity, have been schemed out of sequencing projects earlier, due to high running cost of Sanger sequencing. Consequently, the information about their genomics and key biological processes are inadequate. However, the advent of fast and cost effective next generation sequencing (NGS) platforms in the recent past has enabled the unearthing of certain characteristic gene structures unique to these species. It has also aided in gaining insight about mechanisms underlying processes of gene expression and secondary metabolism as well as facilitated development of genomic resources for diversity characterization, evolutionary analysis and marker assisted breeding even without prior availability of genomic sequence information. In this review we explore how different Next Gen Sequencing platforms, as well as recent advances in NGS based high throughput genotyping technologies are rewarding efforts on de-novo whole genome/transcriptome sequencing, development of genome wide sequence based markers resources for improvement of non-model crops that are less costly than phenotyping. PMID:26734016

  8. The Sumatra great earthquake sequence of 11 April 2012: Evidence of rupture onto multiple subfaults

    NASA Astrophysics Data System (ADS)

    Duputel, Z.; Kanamori, H.; Tsai, V. C.; Rivera, L. A.; Meng, L.; Ampuero, J. P.; Stock, J. M.

    2012-12-01

    Great strike-slip earthquakes are very uncommon and it is known that many of them involve remarkable rupture complexity. On 11 April 2012, the equatorial Indian Ocean was hit by a Mw=8.6 earthquake, followed two hours later by another Mw=8.2 event. These two earthquakes are the largest strike-slip events ever observed and also among the largest intraplate earthquakes instrumentally recorded. Our analysis for the Mw=8.6 mainshock reveals a remarkable rupture complexity and indicates a large centroid depth (~30km). To further resolve the rupture process, we developed a method to invert very long period seismic data for multiple-point-source parameters. The current optimum source model at long period consists of two point sources separated by about 209 km with magnitudes Mw=8.5 and Mw=8.3. To analyze the Mw=8.2 aftershock, we removed the perturbation due to large surface-wave arrivals of the Mw=8.6 mainshock by subtracting the corresponding synthetics. Our results suggests that the Mw=8.2 aftershock had a large centroid depth between 30 km and 40 km. This major earthquake sequence brings a new perspective to the seismotectonics of the equatorial Indian Ocean and reveals active deep lithospheric deformations.

  9. Recognizing Sequences of Sequences

    PubMed Central

    Kiebel, Stefan J.; von Kriegstein, Katharina; Daunizeau, Jean; Friston, Karl J.

    2009-01-01

    The brain's decoding of fast sensory streams is currently impossible to emulate, even approximately, with artificial agents. For example, robust speech recognition is relatively easy for humans but exceptionally difficult for artificial speech recognition systems. In this paper, we propose that recognition can be simplified with an internal model of how sensory input is generated, when formulated in a Bayesian framework. We show that a plausible candidate for an internal or generative model is a hierarchy of ‘stable heteroclinic channels’. This model describes continuous dynamics in the environment as a hierarchy of sequences, where slower sequences cause faster sequences. Under this model, online recognition corresponds to the dynamic decoding of causal sequences, giving a representation of the environment with predictive power on several timescales. We illustrate the ensuing decoding or recognition scheme using synthetic sequences of syllables, where syllables are sequences of phonemes and phonemes are sequences of sound-wave modulations. By presenting anomalous stimuli, we find that the resulting recognition dynamics disclose inference at multiple time scales and are reminiscent of neuronal dynamics seen in the real brain. PMID:19680429

  10. Mouse Genome Database: From sequence to phenotypes and disease models

    PubMed Central

    Richardson, Joel E.; Kadin, James A.; Smith, Cynthia L.; Blake, Judith A.; Bult, Carol J.

    2015-01-01

    Summary The Mouse Genome Database (MGD, www.informatics.jax.org) is the international scientific database for genetic, genomic, and biological data on the laboratory mouse to support the research requirements of the biomedical community. To accomplish this goal, MGD provides broad data coverage, serves as the authoritative standard for mouse nomenclature for genes, mutants, and strains, and curates and integrates many types of data from literature and electronic sources. Among the key data sets MGD supports are: the complete catalog of mouse genes and genome features, comparative homology data for mouse and vertebrate genes, the authoritative set of Gene Ontology (GO) annotations for mouse gene functions, a comprehensive catalog of mouse mutations and their phenotypes, and a curated compendium of mouse models of human diseases. Here, we describe the data acquisition process, specifics about MGD's key data areas, methods to access and query MGD data, and outreach and user help facilities. genesis 53:458–473, 2015. © 2015 The Authors. Genesis Published by Wiley Periodicals, Inc. PMID:26150326

  11. Genome sequence of the model mushroom Schizophyllum commune

    SciTech Connect

    Ohm, Robin A.; de Jong, Jan F.; Lugones, Luis G.; Aerts, Andrea; Kothe, Erika; Stajich, Jason E.; de Vries, Ronald P.; Record, Eric; Levasseur, Anthony; Baker, Scott E.; Bartholomew, Kirk A.; Coutinho, Pedro M.; Erdmann, Susann; Fowler, Thomas J.; Gathman, Allen C.; Lombard, Vincent; Henrissat, Bernard; Knabe, Nicole; Kues, Ursula; Lilly, Walt; Lindquist, Erika; Lucas, Susan; Magnuson, Jon K.; Piumi, Francois; Raudaskoski, Marjatta; Salamov, Asaf; Schmutz, Jeremy; Schwarze, Francis W.; vanKuyk, Patricia A.; Horton, J. S.; Grigoriev, Igor V.; Wosten, Han

    2010-09-01

    Much remains to be learned about the biology of mushroom-forming fungi, which are an important source of food, secondary metabolites and industrial enzymes. The wood-degrading fungus Schizophyllum commune is both a genetically tractable model for studying mushroom development and a likely source of enzymes capable of efficient degradation of lignocellulosic biomass. Comparative analyses of its 38.5-megabase genome, which encodes 13,210 predicted genes, reveal the species's unique wood-degrading machinery. One-third of the 471 genes predicted to encode transcription factors are differentially expressed during sexual development of S. commune. Whereas inactivation of one of these, fst4, prevented mushroom formation, inactivation of another, fst3, resulted in more, albeit smaller, mushrooms than in the wild-type fungus. Antisense transcripts may also have a role in the formation of fruiting bodies. Better insight into the mechanisms underlying mushroom formation should affect commercial production of mushrooms and their industrial use for producing enzymes and pharmaceuticals.

  12. Discounting of reward sequences: a test of competing formal models of hyperbolic discounting.

    PubMed

    Zarr, Noah; Alexander, William H; Brown, Joshua W

    2014-01-01

    Humans are known to discount future rewards hyperbolically in time. Nevertheless, a formal recursive model of hyperbolic discounting has been elusive until recently, with the introduction of the hyperbolically discounted temporal difference (HDTD) model. Prior to that, models of learning (especially reinforcement learning) have relied on exponential discounting, which generally provides poorer fits to behavioral data. Recently, it has been shown that hyperbolic discounting can also be approximated by a summed distribution of exponentially discounted values, instantiated in the μAgents model. The HDTD model and the μAgents model differ in one key respect, namely how they treat sequences of rewards. The μAgents model is a particular implementation of a Parallel discounting model, which values sequences based on the summed value of the individual rewards whereas the HDTD model contains a non-linear interaction. To discriminate among these models, we observed how subjects discounted a sequence of three rewards, and then we tested how well each candidate model fit the subject data. The results show that the Parallel model generally provides a better fit to the human data.

  13. Object relations theory and activity theory: a proposed link by way of the procedural sequence model.

    PubMed

    Ryle, A

    1991-12-01

    An account of object relations theory (ORT), represented in terms of the procedural sequence model (PSM), is compared to the ideas of Vygotsky and activity theory (AT). The two models are seen to be compatible and complementary and their combination offers a satisfactory account of human psychology, appropriate for the understanding and integration of psychotherapy.

  14. Sequence-Based Pronunciation Variation Modeling for Spontaneous ASR Using a Noisy Channel Approach

    NASA Astrophysics Data System (ADS)

    Hofmann, Hansjörg; Sakti, Sakriani; Hori, Chiori; Kashioka, Hideki; Nakamura, Satoshi; Minker, Wolfgang

    The performance of English automatic speech recognition systems decreases when recognizing spontaneous speech mainly due to multiple pronunciation variants in the utterances. Previous approaches address this problem by modeling the alteration of the pronunciation on a phoneme to phoneme level. However, the phonetic transformation effects induced by the pronunciation of the whole sentence have not yet been considered. In this article, the sequence-based pronunciation variation is modeled using a noisy channel approach where the spontaneous phoneme sequence is considered as a “noisy” string and the goal is to recover the “clean” string of the word sequence. Hereby, the whole word sequence and its effect on the alternation of the phonemes will be taken into consideration. Moreover, the system not only learns the phoneme transformation but also the mapping from the phoneme to the word directly. In this study, first the phonemes will be recognized with the present recognition system and afterwards the pronunciation variation model based on the noisy channel approach will map from the phoneme to the word level. Two well-known natural language processing approaches are adopted and derived from the noisy channel model theory: Joint-sequence models and statistical machine translation. Both of them are applied and various experiments are conducted using microphone and telephone of spontaneous speech.

  15. Using Regional Moment Tensors to Constrain Earthquake Processes following the 2010 Darfield and 2011 Canterbury New Zealand Earthquake Sequences

    NASA Astrophysics Data System (ADS)

    Herman, M. W.; Furlong, K. P.; Herrmann, R. B.; Benz, H.

    2011-12-01

    We model regional broadband data from the South Island of New Zealand to determine regional moment tensor solutions for the mainshock and selected aftershocks of the M7.0, 3 September 2011, M6.1, 21 February 2011 and M6.0 13 June 2011 earthquakes that occurred near Christchurch, New Zealand. Arrival time picks from both the local and regional strong motion and broadband data were used to determine preliminary earthquake locations using a previously published South Island velocity model. Rayleigh and Love surface wave dispersion measurements were then made from selected events to refine the velocity model in order to better match the predominantly large regional surface waves. RMT solutions were computed using the procedures of Herrmann et al. (2011). In total, we computed RMT solutions for 82 events in the magnitude range of Mw3.5-7.0. Although the crustal faulting behavior in the region has been argued to reflect a complex interaction of strike slip and thrust faulting, the dominant faulting style in the sequence is right-lateral, strike-slip (75 events), with nodal planes striking west-east to southwest-northeast. There are only five purely reverse mechanisms, at the western end of the sequence, in the vicinity of the Harper Hills blind thrust. The main Mw 7.0 rupture shows both local small-scale stepovers and one larger (~ 5-10 km width) right stepover near 172.40°E. Although we expect normal faulting associated with this larger stepover, during the first month after the main shock we observe only two normal fault mechanisms and 13 strike slip (inferred E-W right-lateral) events in the stepover region, and since that time, the sense of faulting has been dominated by right-lateral, strike-slip events, perhaps indicating a sequence of short E-W fault segments in the region. The February and June 2011 events occurred along the same trend at the eastern end of the sequence, and show similar strike slip mechanisms to the majority of events to the west, but the

  16. Precision Measurements of the Cluster Red Sequence using an Error Corrected Gaussian Mixture Model

    SciTech Connect

    Hao, Jiangang; Koester, Benjamin P.; Mckay, Timothy A.; Rykoff, Eli S.; Rozo, Eduardo; Evrard, August; Annis, James; Becker, Matthew; Busha, Michael; Gerdes, David; Johnston, David E.; /Northwestern U. /Brookhaven

    2009-07-01

    The red sequence is an important feature of galaxy clusters and plays a crucial role in optical cluster detection. Measurement of the slope and scatter of the red sequence are affected both by selection of red sequence galaxies and measurement errors. In this paper, we describe a new error corrected Gaussian Mixture Model for red sequence galaxy identification. Using this technique, we can remove the effects of measurement error and extract unbiased information about the intrinsic properties of the red sequence. We use this method to select red sequence galaxies in each of the 13,823 clusters in the maxBCG catalog, and measure the red sequence ridgeline location and scatter of each. These measurements provide precise constraints on the variation of the average red galaxy populations in the observed frame with redshift. We find that the scatter of the red sequence ridgeline increases mildly with redshift, and that the slope decreases with redshift. We also observe that the slope does not strongly depend on cluster richness. Using similar methods, we show that this behavior is mirrored in a spectroscopic sample of field galaxies, further emphasizing that ridgeline properties are independent of environment. These precise measurements serve as an important observational check on simulations and mock galaxy catalogs. The observed trends in the slope and scatter of the red sequence ridgeline with redshift are clues to possible intrinsic evolution of the cluster red-sequence itself. Most importantly, the methods presented in this work lay the groundwork for further improvements in optically-based cluster cosmology.

  17. The great 1933 Sanriku-oki earthquake: reappraisal of the main shock and its aftershocks and implications for its tsunami using regional tsunami and seismic data

    NASA Astrophysics Data System (ADS)

    Uchida, Naoki; Kirby, Stephen H.; Umino, Norihito; Hino, Ryota; Kazakami, Tomoe

    2016-09-01

    be explained from a single high-angle fault confined at a shallow depth (depth ≦50 km). The upward motion of the 1933 tsunami waveform records observed at Sanriku coast also cannot be explained from a single high-angle west-dipping normal fault. If we consider additional fault, involvement of high-angle, east-dipping normal faults can better explain the tsunami first motion and triggering of the aftershock in a wide area under the outer trench slope. Therefore multiple off-trench normal faults may have activated during the 1933 earthquake. We also relocated recent (2001-2012) seismicity by the same method. The results show that the present seismicity in the outer-trench-slope region can be divided into several groups along the trench. Comparison of the 1933 rupture dimensions based on our aftershock relocations with the morphologies of fault scarps in the outer trench slope suggest that the rupture was limited to the region where fault scarps are largely trench parallel and cross cut the seafloor spreading fabric. These findings imply that bending geometry and structural segmentation of the incoming plate largely controls the spatial extent of the 1933 seismogenic faulting. In this shallow rupture model for this largest outer trench earthquake, triggered seismicity in the forearc and structural control of faulting represent an important deformation styles for off-trench and shallow megathrust zones.

  18. Modeling Seismicity Rate Changes in Oklahoma and Arkansas

    NASA Astrophysics Data System (ADS)

    Llenos, A. L.; Michael, A. J.

    2012-12-01

    The rate of M≥3 earthquakes in the central and eastern US increased beginning in 2009, particularly in regions such as Oklahoma and central Arkansas where fluid injection has occurred (Ellsworth et al., SSA abs, 2012; Horton, SRL, 2012). We compare rate changes observed in Oklahoma, which had a low background seismicity rate before 2009, to rate changes observed in central Arkansas, which had swarms prior to the start of wastewater injection (Chiu et al., BSSA, 1984; Horton, SRL, 2012). In both cases, stochastic Epidemic-Type Aftershock Sequence (ETAS) models (Ogata, JASA, 1988) and statistical tests demonstrate that the background rate of independent events and the aftershock productivity must increase in 2009 in order to explain the observed increase in seismicity. Productivity is lower during the earlier tectonic swarms in Arkansas. The change in aftershock productivity may provide a way to distinguish manmade from natural earthquake rate changes and could provide insights into the physical mechanisms of induced seismicity. We fit the ETAS model, which is based on empirical aftershock scaling laws such as Omori's Law and the Gutenberg-Richter magnitude distribution, to a 1973-2011 USGS PDE catalog of M≥3 Oklahoma earthquakes and a 1982-2012 ANSS catalog of M≥2.2 Arkansas earthquakes. To determine whether a rate increase is due to a change in background seismicity rate, aftershock productivity, or some combination of the two, we do the following: 1) fit the model parameters to the data, 2) convert origin times to transformed times (Ogata, JGR, 1992), and 3) use Runs and autocorrelation function tests to test the null hypothesis that the transformed times are drawn from a Poisson distribution with constant rate (as expected when no external processes trigger earthquakes besides a constant tectonic loading rate). In both cases a single set of parameters cannot fit the entire time period, suggesting that significant changes in the underlying process occurred

  19. Training the max-margin sequence model with the relaxed slack variables.

    PubMed

    Niu, Lingfeng; Wu, Jianmin; Shi, Yong

    2012-09-01

    Sequence models are widely used in many applications such as natural language processing, information extraction and optical character recognition, etc. We propose a new approach to train the max-margin based sequence model by relaxing the slack variables in this paper. With the canonical feature mapping definition, the relaxed problem is solved by training a multiclass Support Vector Machine (SVM). Compared with the state-of-the-art solutions for the sequence learning, the new method has the following advantages: firstly, the sequence training problem is transformed into a multiclassification problem, which is more widely studied and already has quite a few off-the-shelf training packages; secondly, this new approach reduces the complexity of training significantly and achieves comparable prediction performance compared with the existing sequence models; thirdly, when the size of training data is limited, by assigning different slack variables to different microlabel pairs, the new method can use the discriminative information more frugally and produces more reliable model; last but not least, by employing kernels in the intermediate multiclass SVM, nonlinear feature space can be easily explored. Experimental results on the task of named entity recognition, information extraction and handwritten letter recognition with the public datasets illustrate the efficiency and effectiveness of our method.

  20. Estimating genomic distance from DNA sequence location in cell nuclei by a random walk model

    SciTech Connect

    Engh, G. van den; Trask, B.J. ); Sachs, R. )

    1992-09-04

    The folding of chromatin in interphase cell nuclei was studied by fluorescent in situ hybridization with pairs of unique DNA sequence probes. The sites of DNA sequences separated by 100 to 2000 kilobase pairs (kbp) are distributed in interphase chromatin according to a random walk model. This model provides the basis for calculating the spacing of sequences along the linear DNA molecule from interphase distance measurements. An interphase mapping strategy based on this model was tested with 13 probes from a 4-megabase pair (Mbp) region of chromosome 4 containing the Huntington disease locus. The results confirmed the locations of the probes and showed that the remaining gap in the published maps of this region is negligible in size. Interphase distance measurements should facilitate construction of chromosome maps with an average marker density of one per 100 kbp, approximately ten times greater than that achieved by hybridization to metaphase chromosomes.

  1. Estimating Genomic Distance from DNA Sequence Location in Cell Nuclei by a Random Walk Model

    NASA Astrophysics Data System (ADS)

    van den Engh, Ger; Sachs, Rainer; Trask, Barbara J.

    1992-09-01

    The folding of chromatin in interphase cell nuclei was studied by fluorescent in situ hybridization with pairs of unique DNA sequence probes. The sites of DNA sequences separated by 100 to 2000 kilobase pairs (kbp) are distributed in interphase chromatin according to a random walk model. This model provides the basis for calculating the spacing of sequences along the linear DNA molecule from interphase distance measurements. An interphase mapping strategy based on this model was tested with 13 probes from a 4-megabase pair (Mbp) region of chromosome 4 containing the Huntington disease locus. The results confirmed the locations of the probes and showed that the remaining gap in the published maps of this region is negligible in size. Interphase distance measurements should facilitate construction of chromosome maps with an average marker density of one per 100 kbp, approximately ten times greater than that achieved by hybridization to metaphase chromosomes.

  2. Structured prediction models for RNN based sequence labeling in clinical text

    PubMed Central

    Jagannatha, Abhyuday N; Yu, Hong

    2016-01-01

    Sequence labeling is a widely used method for named entity recognition and information extraction from unstructured natural language data. In clinical domain one major application of sequence labeling involves extraction of medical entities such as medication, indication, and side-effects from Electronic Health Record narratives. Sequence labeling in this domain, presents its own set of challenges and objectives. In this work we experimented with various CRF based structured learning models with Recurrent Neural Networks. We extend the previously studied LSTM-CRF models with explicit modeling of pairwise potentials. We also propose an approximate version of skip-chain CRF inference with RNN potentials. We use these methodologies1 for structured prediction in order to improve the exact phrase detection of various medical entities. PMID:28004040

  3. Using single cell sequencing data to model the evolutionary history of a tumor

    PubMed Central

    2014-01-01

    Background The introduction of next-generation sequencing (NGS) technology has made it possible to detect genomic alterations within tumor cells on a large scale. However, most applications of NGS show the genetic content of mixtures of cells. Recently developed single cell sequencing technology can identify variation within a single cell. Characterization of multiple samples from a tumor using single cell sequencing can potentially provide information on the evolutionary history of that tumor. This may facilitate understanding how key mutations accumulate and evolve in lineages to form a heterogeneous tumor. Results We provide a computational method to infer an evolutionary mutation tree based on single cell sequencing data. Our approach differs from traditional phylogenetic tree approaches in that our mutation tree directly describes temporal order relationships among mutation sites. Our method also accommodates sequencing errors. Furthermore, we provide a method for estimating the proportion of time from the earliest mutation event of the sample to the most recent common ance