@article{BeauvalHainzlScherbaum2006, author = {Beauval, Celine and Hainzl, Sebastian and Scherbaum, Frank}, title = {The impact of the spatial uniform distribution of seismicity on probabilistic seismic-hazard estimation}, series = {Bulletin of the Seismological Society of America}, volume = {96}, journal = {Bulletin of the Seismological Society of America}, number = {6}, publisher = {GeoScienceWorld}, address = {Alexandria, Va.}, issn = {0037-1106}, doi = {10.1785/0120060073}, pages = {2465 -- 2471}, year = {2006}, abstract = {The first step in the estimation of probabilistic seismic hazard in a region commonly consists of the definition and characterization of the relevant seismic sources. Because in low-seismicity regions seismicity is often rather diffuse and faults are difficult to identify, large areal source zones are mostly used. The corresponding hypothesis is that seismicity is uniformly distributed inside each areal seismic source zone. In this study, the impact of this hypothesis on the probabilistic hazard estimation is quantified through the generation of synthetic spatial seismicity distributions. Fractal seismicity distributions are generated inside a given source zone and probabilistic hazard is computed for a set of sites located inside this zone. In our study, the impact of the spatial seismicity distribution is defined as the deviation from the hazard value obtained for a spatially uniform seismicity distribution. From the generation of a large number of synthetic distributions, the correlation between the fractal dimension D and the impact is derived. The results show that the assumption of spatially uniform seismicity tends to bias the hazard to higher values. The correlation can be used to determine the systematic biases and uncertainties for hazard estimations in real cases, where the fractal dimension has been determined. We apply the technique in Germany (Cologne area) and in France (Alps).}, language = {en} } @article{ScherbaumCottonStaedtke2006, author = {Scherbaum, Frank and Cotton, Fabrice Pierre and Staedtke, Helmut}, title = {The estimation of minimum-misfit stochastic models from empirical ground-motion prediction equations}, doi = {10.1785/0120050015}, year = {2006}, abstract = {In areas of moderate to low seismic activity there is commonly a lack of recorded strong ground motion. As a consequence, the prediction of ground motion expected for hypothetical future earthquakes is often performed by employing empirical models from other regions. In this context, Campbell's hybrid empirical approach (Campbell, 2003, 2004) provides a methodological framework to adapt ground-motion prediction equations to arbitrary target regions by using response spectral host-to-target-region-conversion filters. For this purpose, the empirical ground-motion prediction equation has to be quantified in terms of a stochastic model. The problem we address here is how to do this in a systematic way and how to assess the corresponding uncertainties. For the determination of the model parameters we use a genetic algorithm search. The stochastic model spectra were calculated by using a speed-optimized version of SMSIM (Boore, 2000). For most of the empirical ground-motion models, we obtain sets of stochastic models that match the empirical models within the full magnitude and distance ranges of their generating data sets fairly well. The overall quality of fit and the resulting model parameter sets strongly depend on the particular choice of the distance metric used for the stochastic model. We suggest the use of the hypocentral distance metric for the stochastic Simulation of strong ground motion because it provides the lowest-misfit stochastic models for most empirical equations. This is in agreement with the results of two recent studies of hypocenter locations in finite-source models which indicate that hypocenters are often located close to regions of large slip (Mai et al., 2005; Manighetti et al., 2005). Because essentially all empirical ground-motion prediction equations contain data from different geographical regions, the model parameters corresponding to the lowest-misfit stochastic models cannot necessarily be expected to represent single, physically realizable host regions but to model the generating data sets in an average way. In addition, the differences between the lowest-misfit stochastic models and the empirical ground-motion prediction equation are strongly distance, magnitude, and frequency dependent, which, according to the laws of uncertainty propagation, will increase the variance of the corresponding hybrid empirical model predictions (Scherbaum et al., 2005). As a consequence, the selection of empirical ground-motion models for host-to-target-region conversions requires considerable judgment of the ground-motion analyst}, language = {en} } @article{BeauvalHainzlScherbaum2006, author = {Beauval, C{\´e}line and Hainzl, Sebastian and Scherbaum, Frank}, title = {Probabilistic seismic hazard estimation in low-seismicity regions considering non-Poissonian seismic occurrence}, issn = {0956-540X}, doi = {10.1111/j.1365-246X.2006.02863.x}, year = {2006}, abstract = {In low-seismicity regions, such as France or Germany, the estimation of probabilistic seismic hazard must cope with the difficult identification of active faults and with the low amount of seismic data available. Since the probabilistic hazard method was initiated, most studies assume a Poissonian occurrence of earthquakes. Here we propose a method that enables the inclusion of time and space dependences between earthquakes into the probabilistic estimation of hazard. Combining the seismicity model Epidemic Type Aftershocks-Sequence (ETAS) with a Monte Carlo technique, aftershocks are naturally accounted for in the hazard determination. The method is applied to the Pyrenees region in Southern France. The impact on hazard of declustering and of the usual assumption that earthquakes occur according to a Poisson process is quantified, showing that aftershocks contribute on average less than 5 per cent to the probabilistic hazard, with an upper bound around 18 per cent}, language = {en} } @article{DialloKuleshHolschneideretal.2006, author = {Diallo, Mamadou Sanou and Kulesh, Michail and Holschneider, Matthias and Kurennaya, Kristina and Scherbaum, Frank}, title = {Instantaneous polarization attributes based on an adaptive approximate covariance method}, series = {Geophysics}, volume = {71}, journal = {Geophysics}, number = {5}, publisher = {SEG}, address = {Tulsa}, issn = {0016-8033}, doi = {10.1190/1.2227522}, pages = {V99 -- V104}, year = {2006}, abstract = {We introduce a method for computing instantaneous-polarization attributes from multicomponent signals. This is an improvement on the standard covariance method (SCM) because it does not depend on the window size used to compute the standard covariance matrix. We overcome the window-size problem by deriving an approximate analytical formula for the cross-energy matrix in which we automatically and adaptively determine the time window. The proposed method uses polarization analysis as applied to multicomponent seismic by waveform separation and filtering.}, language = {en} } @article{DouglasBungumScherbaum2006, author = {Douglas, John and Bungum, Hilmar and Scherbaum, Frank}, title = {Ground-motion prediction equations for Southern Spain and Southern Norway obtained using the composite model perspective}, issn = {1363-2469}, doi = {10.1080/1363246060935058}, year = {2006}, abstract = {In this paper, two sets of earthquake ground-motion relations to estimate peak ground and response spectral acceleration are developed for sites in southern Spain and in southern Norway using a recently published composite approach. For this purpose seven empirical ground-motion relations developed from recorded strong-motion data from different parts of the world were employed. The different relations were first adjusted based on a number of transformations to convert the differing choices of independent parameters to a single one. After these transformations, which include the scatter introduced, were performed, the equations were modified to account for differences between the host and the target regions using the stochastic method to compute the host-to-target conversion factors. Finally functions were fitted to the derived ground-motion estimates to obtain sets of seven individual equations for use in probabilistic seismic hazard assessment for southern Spain and southern Norway. The relations are compared with local ones published for the two regions. The composite methodology calls for the setting up of independent logic trees for the median values and for the sigma values, in order to properly separate epistemic and aleatory uncertainties after the corrections and the conversions}, language = {en} } @article{SuryantoIgelWassermannetal.2006, author = {Suryanto, Wiwit and Igel, Heiner and Wassermann, Joachim and Cochard, Alain and Schuberth, B. S. A. and Vollmer, Daniel and Scherbaum, Frank and Schreiber, U. and Velikoseltsev, A.}, title = {First comparison of array-derived rotational ground motions with direct ring laser measurements}, series = {Bulletin of the Seismological Society of America}, volume = {96}, journal = {Bulletin of the Seismological Society of America}, number = {6}, publisher = {GeoScienceWorld}, address = {Alexandria, Va.}, issn = {0037-1106}, doi = {10.1785/0120060004}, pages = {2059 -- 2071}, year = {2006}, abstract = {Recently, ring laser technology has provided the first consistent observations of rotational ground motions around a vertical axis induced by earthquakes. "Consistent," in this context, implies that the observed waveforms and amplitudes are compatible with collocated recordings of translational ground motions. In particular, transverse accelerations should be in phase with rotation rate and their ratio proportional to local horizontal phase velocity assuming plane-wave propagation. The ring laser installed at the Fundamental station Wettzell in the Bavarian Forest, Southeast Germany, is recording the rotation rate around a vertical axis, theoretically a linear combination of the space derivatives of the horizontal components of motion. This suggests that, in principle, rotation can be derived from seismic-array experiments by "finite differencing." This has been attempted previously in several studies; however, the accuracy of these observations could never be tested in the absence of direct measurements. We installed a double cross-shaped array of nine stations from December 2003 to March 2004 around the ring laser instrument and observed several large earthquakes on both the ring laser and the seismic array. Here we present for the first time a comparison of array-derived rotations with direct measurements of rotations for ground motions induced by the M 6.3 Al Hoceima, Morocco, earthquake of 24 February 2004. With complete 3D synthetic seismograms calculated for this event we show that even low levels of noise may considerably influence the accuracy of the array-derived rotations when the minimum number of required stations (three) is used. Nevertheless, when using all nine stations, the overall fit between direct and array-derived measurements is surprisingly good (maximum correlation coefficient of 0.94).}, language = {en} } @article{HainzlScherbaumBeauval2006, author = {Hainzl, Sebastian and Scherbaum, Frank and Beauval, C{\´e}line}, title = {Estimating background activity based on interevent-time distribution}, issn = {0037-1106}, doi = {10.1785/0120050053}, year = {2006}, abstract = {The statistics of time delays between successive earthquakes has recently been claimed to be universal and to show the existence of clustering beyond the duration of aftershock bursts. We demonstrate that these claims are unjustified. Stochastic simulations with Poissonian background activity and triggered Omori-type aftershock sequences are shown to reproduce the interevent-time distributions observed on different spatial and magnitude scales in California. Thus the empirical distribution can be explained without any additional long-term clustering. Furthermore, we find that the shape of the interevent-time distribution, which can be approximated by the gamma distribution, is determined by the percentage of main-shocks in the catalog. This percentage can be calculated by the mean and variance of the interevent times and varies between 5\% and 90\% for different regions in California. Our investigation of stochastic simulations indicates that the interevent-time distribution provides a nonparametric reconstruction of the mainshock magnitude-frequency distribution that is superior to standard declustering algorithm}, language = {en} } @article{DialloKuleshHolschneideretal.2006, author = {Diallo, Mamadou Sanou and Kulesh, Michail and Holschneider, Matthias and Scherbaum, Frank and Adler, Frank}, title = {Characterization of polarization attributes of seismic waves using continuous wavelet transforms}, issn = {0016-8033}, doi = {10.1190/1.2194511}, year = {2006}, abstract = {Complex-trace analysis is the method of choice for analyzing polarized data. Because particle motion can be represented by instantaneous attributes that show distinct features for waves of different polarization characteristics, it can be used to separate and characterize these waves. Traditional methods of complex-trace analysis only give the instantaneous attributes as a function of time or frequency. However. for transient wave types or seismic events that overlap in time, an estimate of the polarization parameters requires analysis of the time-frequency dependence of these attributes. We propose a method to map instantaneous polarization attributes of seismic signals in the wavelet domain and explicitly relate these attributes with the wavelet-transform coefficients of the analyzed signal. We compare our method with traditional complex-trace analysis using numerical examples. An advantage of our method is its possibility of performing the complete wave-mode separation/ filtering process in the wavelet domain and its ability to provide the frequency dependence of ellipticity, which contains important information on the subsurface structure. Furthermore, using 2-C synthetic and real seismic shot gathers, we show how to use the method to separate different wave types and identify zones of interfering wave modes}, language = {en} } @article{EwaldIgelHinzenetal.2006, author = {Ewald, Michael and Igel, Heiner and Hinzen, Klaus-G{\"u}nther and Scherbaum, Frank}, title = {Basin-related effects on ground motion for earthquake scenarios in the Lower Rhine Embayment}, issn = {0956-540X}, doi = {10.1111/j.1365-246X.2006.02909.x}, year = {2006}, abstract = {The deterministic calculation of earthquake scenarios using complete waveform modelling plays an increasingly important role in estimating shaking hazard in seismically active regions. Here we apply 3-D numerical modelling of seismic wave propagation to M 6+ earthquake scenarios in the area of the Lower Rhine Embayment, one of the seismically most active regions in central Europe. Using a 3-D basin model derived from geology, borehole information and seismic experiments, we aim at demonstrating the strong dependence of ground shaking on hypocentre location and basin structure. The simulations are carried out up to frequencies of ca. 1 Hz. As expected, the basin structure leads to strong lateral variations in peak ground motion, amplification and shaking duration. Depending on source-basin-receiver geometry, the effects correlate with basin depth and the slope of the basin flanks; yet, the basin also affects peak ground motion and estimated shaking hazard thereof outside the basin. Comparison with measured seismograms for one of the earthquakes shows that some of the main characteristics of the wave motion are reproduced. Cumulating the derived seismic intensities from the three modelled earthquake scenarios leads to a predominantly basin correlated intensity distribution for our study area}, language = {en} }