bluuebunny/crossref_metadata_2025_split huggingface dataset:
Site amplification in the San Fernando Valley, California: Variability of site-effect estimation using theS-wave, coda, andH/Vmethods
Authors: Bonilla Luis Fabián , Steidl Jamison H. , Lindley Grant T. , Tumarkin Alexei G. , Archuleta Ralph J. 
Published: September 2021

AbstractDuring the months that followed the 17 January 1994 M 6.7 Northridge, California, earthquake, portable digital seismic stations were deployed in the San Fernando basin to record aftershock data and estimate site-amplification factors. This study analyzes data, recorded on 31 three-component stations, from 38 aftershocks ranging from M 3.0 to M 5.1, and depths from 0.2 to 19 km. Site responses from the 31 stations are estimated from coda waves, S waves, and ratios of horizontal to vertical (H/V) recordings. For the coda and the S waves, site response is estimated using both direct spectral ratios and a generalized inversion scheme. Results from the inversions indicate that the effect of Qs can be significant, especially at high frequencies. Site amplifications estimated from the coda of the vertical and horizontal components can be significantly different from each other, depending on the choice of the reference site. The difference is reduced when an average of six rock sites is used as a reference site. In addition, when using this multi-reference site, the coda amplification from rock sites is usually within a factor of 2 of the amplification determined from the direct spectral ratios and the inversion of the S waves. However, for nonrock sites, the coda amplification can be larger by a factor of 2 or more when compared with the amplification estimated from the direct spectral ratios and the inversion of the S waves. The H/V method for estimating site response is found to extract the same predominant peaks as the direct spectral ratio and the inversion methods. The amplifications determined from the H/V method are, however, different from the amplifications determined from the other methods. Finally, the stations were grouped into classes based on two different classifications, general geology and a more detailed classification using a quaternary geology map for the Los Angeles and San Fernando areas. Average site-response estimates using the site characterization based on the detailed geology show better correlation between amplification and surface geology than the general geology classification.
Moho dip and crustal anisotropy in northwestern Nevada from teleseismic receiver functions
Authors: Peng Xiaohua , Humphreys Eugene D. 
Published: September 2021

AbstractReceiver functions are derived from teleseismic waves recorded during the 1988 to 1989 PASSCAL Basin and Range passive-source seismic experiment in northwestern Nevada. A velocity model involving both a planar dipping Moho and crustal anisotropy is needed to explain the radial and tangential motions of the observed PS conversions. An arrival-time difference often observed between radial and tangential Moho PS conversions suggests an anisotropic crust. The PS conversions are large and indicate a major discontinuity under the area. The particle motion directions for most of the tangential components change sign between South American events and events from the other two source areas (Japan and Tonga regions), providing good evidence for a Moho dipping approximately to the north. Also, the PS conversions from the Moho follow direct P arrivals by about 3.2 sec under the southern part of the array, 3.4 sec under the southern central part of the array, and 3.7 sec under the northern part of the array, indicating a Moho that varies in depth from about 26 to 31 km. A velocity model with the Moho dipping ∼9° in a nearly northerly direction and an anisotropic crust with a split time of ∼0.25 sec and a fast axis of ∼130° best explain these observations.
Stable baseline correction of digital strong-motion data
Authors: Chiu Hung-Chie 
Published: September 2021

AbstractMost baseline errors of analog strong-motion data still exist in highresolution data. In this study, we identify the major baseline errors of digital strong-motion data and propose a three-step algorithm to correct these errors. The major baseline errors found in these digital data consist of constant drift in the acceleration, low-frequency instrument noise, low-frequency background noise, the small initial values for acceleration and velocity, and manipulation errors. This threestep algorithm includes fitting the baseline of acceleration by the least squares, applying a high-pass filter in acceleration, and subtracting the initial values in velocity. A least-squares fit of a straight line before filtering can effectively remove the baseline drift in acceleration. Then, the filtering removes the linear trend and other low-frequency errors that exist in the acceleration. Finally, the subtracting of the initial velocity removes the linear trend of displacement. Among these three steps, only the filtering in the second step may introduce a side effect. Compared to the Volume II routine developed by Trifunac and Lee (1973), this three-step processing significantly reduces computational efforts and side effects resulting from unnecessary manipulation of data. This algorithm has been successfully tested on several types of digital strong-motion data. Several independent validations show that the proposed algorithm is stable.
Fault location and rupture kinematics of the magnitude 6.8, 1992 Erzincan earthquake, Turkey, from strong ground motion and regional records
Authors: Bernard Pascal , Gariel Jean-Christophe , Dorbath Louis 
Published: September 2021

Abstract
The hypocenter location of the 13 March 1992, M = 6.9 Erzincan earthquake (Turkey) and its rupture kinematics have been studied using local and regional seismic records to understand its relationship with the tectonic activity of the Erzincan basin and of the North Anatolian fault (NAF). Regional records of the mainshock and the largest aftershocks were used to locate the respective epicenters. The mainshock S-P travel time delay and the P-wave polarization of the near-source accelerogram record in Erzincan (ERZ), calibrated by the aftershock records, constrain the mainshock hypocenter to be located about 10 km to the east-southeast of Erzincan, 39°42.3 N, 39°35.2 E, and at a best-fit depth of about 9 km. The activated fault is a major branch of the NAF along the eastern edge of the basin. Hypocentral depths greater than about 16 km are not supported by the data. The ground velocity record at ERZ has been synthesized for constraining the northwestward rupture, assuming a kinematic model with constant slip and rupture velocity, and a strike 125°, for a large number of models. The latter were constructed by varying the rupture parameters in a discrete domain. The best-fit fault models are located within 1 km of the epicenter above and have all their northwestern end within 5 km of ERZ. The up-dip limit of the rupture in the vicinity of ERZ ranges from 5 to 2 km in depth, in agreement with the absence of surface breakage. The estimated rupture velocity is 3 km/sec; the rise time is 0.35 sec; and the mean slip of about 1 m is poorly resolved, with a standard uncertainty of 0.5 m, being strongly sensitive to the rupture velocity and to the fault location. Combining these results with the seismic moment and the source duration provided by other studies leads to a total rupture length ranging between 20 and 35 km. The rupture thus propagated bilaterally on the NAF and was confined within the limits of the basin, stopping to the southeast near the intersection of the NAF with the Ovaçik fault.
Far-field pulse shapes from circular sources with variable rupture velocities
Authors: Deichmann Nicholas 
Published: September 2021

AbstractRecently, Sato (1994) developed a simple earthquake source model of a circular rupture expanding outward from the center of a fault with constant stress drop. In contrast to previous models, the rupture velocity is allowed to vary over the duration of faulting. This model is used to synthesize apparent moment-rate functions for a three-stage source process: first, the rupture starts out with a gradually increasing velocity, then, it continues to expand uniformly until, finally, it slows to a gradual stop. Synthetic velocity seismograms are obtained from a convolution of the apparent moment-rate functions with a causal Q-operator and an appropriate instrument response. Comparisons with an example of an earthquake signal show that, in the context of the proposed model, the observed emergent P-wave onset, which is not compatible with a constant rupture velocity, can be explained by a gradually accelerating rupture front. Systematic departures from the generally expected scaling relationship between seismic moment and rupture duration are often interpreted as evidence for a dependence of stress drop on seismic moment. However, the trade-off between stress drop and rupture velocity inherent in all kinematic source models implies that such deviations can just as well be attributed to systematic variations of rupture velocity. Whereas, in general, the total duration of the far-field displacement pulse is shorter for P waves than for S waves, the model predicts that the rise time, τ1/2, of the displacement pulse should be longer for P waves than for S waves. This feature could constitute a critical test of the model and also provide a constraint on the rupture velocity.
A comparison of select trigger algorithms for automated global seismic phase and event detection
Authors: Withers Mitchell , Aster Richard , Young Christopher , Beiriger Judy , Harris Mark , Moore Susan , Trujillo Julian 
Published: September 2021

AbstractDigital algorithms for robust detection of phase arrivals in the presence of stationary and nonstationary noise have a long history in seismology and have been exploited primarily to reduce the amount of data recorded by data logging systems to manageable levels. In the present era of inexpensive digital storage, however, such algorithms are increasingly being used to flag signal segments in continuously recorded digital data streams for subsequent processing by automatic and/or expert interpretation systems. In the course of our development of an automated, near-real-time, waveform correlation event-detection and location system (WCEDS), we have surveyed the abilities of such algorithms to enhance seismic phase arrivals in teleseismic data streams. Specifically, we have considered envelopes generated by energy transient (STA/LTA), Z-statistic, frequency transient, and polarization algorithms. The WCEDS system requires a set of input data streams that have a smooth, low-amplitude response to background noise and seismic coda and that contain peaks at times corresponding to phase arrivals. The algorithm used to generate these input streams from raw seismograms must perform well under a wide range of source, path, receiver, and noise scenarios. Present computational capabilities allow the application of considerably more robust algorithms than have been historically used in real time. However, highly complex calculations can still be computationally prohibitive for current workstations when the number of data streams become large. While no algorithm was clearly optimal under all source, receiver, path, and noise conditions tested, an STA/LTA algorithm incorporating adaptive window lengths controlled by nonstationary seismogram spectral characteristics was found to provide an output that best met the requirements of a global correlation-based event-detection and location system.
Determination of Δσ andκ0 from response spectra of large earthquakes in Greece
Authors: Margaris Basil N. , Boore David M. 
Published: September 2021

AbstractWe fit an ω−2 model to response spectra from eight recent Greek earthquakes ranging in size from M = 5.8 to M = 6.9. The diminution parameter κ0 was determined for each site, with a value near 0.06 for a typical soil site. The stress parameter (Δσ) showed little variation from earthquake to earthquake and had a mean value of 56 bars over all earthquakes. Predictions of peak velocity, peak acceleration, rupture duration, and fault length using the derived stress parameters are consistent with observations. Frequency-dependent site amplifications were included in all estimates; the combined effect of amplification and attenuation had a maximum value close to a factor of 2.5 for a typical soil site, relative to the motions at the surface of a perfectly elastic uniform half-space composed of materials near the source. The results form the foundation for predictions of strong motions in Greece for distances and magnitudes other than those for which data are available.
Source model of the 1995 Hyogo-Ken Nanbu earthquake and simulation of near-source ground motion
Authors: Kamae Katsuhiro , Irikura Kojiro 
Published: September 2021

AbstractThe 1995 Hyogo-Ken Nanbu earthquake struck the heavily populated Kobe and adjacent cities in western Japan. More than 6400 people were killed, and more than 150,000 buildings were destroyed. The characteristics of mainshock ground motions in the heavily damaged area are needed to understand how buildings and bridges performed and why they reached failure. Unfortunately, very few strong ground motions were recorded in the heavily damaged area during the mainshock. In this study, we attempt to estimate mainshock ground motions by using the empirical Green's function method (EGF method). First, we assume an initial source model with the asperities based on the rupture process obtained by inversion of strong-ground-motion records. For simplicity, we consider each asperity as a subevent with uniform stress drop in a finite extent. Then, the initial model was improved by matching the synthetic and observed ground motions using a trial-and-error procedure. The final model consists of three subevents: subevent 1 with stress drop of 163 bars, under the Akashi Strait around the rupture starting point; subevent 2 with stress drop of 86 bars, under the Nojima Fault in Awaji Island; and subevent 3 with stress drop of 86 bars, under Kobe. Finally, we estimate strong ground motions using aftershock records at sites where the mainshock was not recorded. The near-source motions in Kobe synthesized with the best-fit model are characterized by two large pulses with a duration of 1 to 3 sec. The pulses are caused by forward rupture directivity effects from subevents 1 and 3. Peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1000 cm/sec2 and 130 cm/sec, respectively, while those at a rock site in the near-source region are about 300 cm/sec2 and 60 cm/sec.
Predictions of shear-wave velocities in southern California using surface geology
Authors: Park Stephen , Elrick Scott 
Published: September 2021

AbstractA new model of the average shear-wave velocity in the uppermost 30 m has been generated by extrapolation of discrete velocity profiles using surface geology at several scales. Statistical methods have been applied to create a map that is no more complicated than is supported by the velocity data; several geologic units with similar responses are grouped together. The resulting map is simpler than previous ones and yet fits the observed velocity profiles better than earlier, more complicated maps. Analysis within a geographic information system will permit updates and modification of the map as new velocity data are added.
Discriminating ripple-fired explosions with high-frequency (&gt; 16 Hz) data
Authors: Carr Dorthe B. , Garbin H. Douglas 
Published: September 2021

Abstract
Most ripple-fired explosions have a unique signature in the spectrum that can be used to quickly identify them when monitoring the Comprehensive Test Ban Treaty. We want to know the importance of high-frequency (&gt; 16 Hz) seismic data in identifying these explosions. The deployable seismic verification system (DSVS) in Wyoming records data up to 50 Hz with good signal to noise, so it is an excellent source for determining the benefits of recording data over 16 Hz. We developed a database of 118 known earthquakes and 176 known ripple-fired explosions. We calculated a binary spectrogram and an average binary spectrum for each event and developed criteria based on the number of peaks and nulls above certain thresholds to classify events as ripple-fired explosions. Using data at frequencies up to 50 Hz, 50% of the known ripple-fired explosions were correctly identified, and another 22% had banding in the spectrogram but did not meet the established criteria. The other 27% of the known ripple-fired explosions had no banding. To test the importance of high-frequency (&gt; 16 Hz) data, we recalculated spectrograms between 0 and 16 Hz for the 135 known ripple-fired explosions and earthquakes that had banding. Eleven of the 135 could not be identified correctly if data over 16 Hz was excluded; 5 had information at frequencies over 16 Hz that was critical to seeing any banding. But the vast majority of events were correctly identified in the pass band of 0 to 16 Hz, suggesting that higher-frequency data do not significantly help to identify most ripple-fired explosions in Wyoming.
Global CMT analysis of moderate earthquakes,Mw≧ 4.5, using intermediate-period surface waves
Authors: Arvidsson Ronald , Ekström Göran 
Published: September 2021

AbstractA new method for calculating centroid moment tensor (CMT) solutions for moderate-sized earthquakes is presented and tested. In the new algorithm, which is a modification to the standard Harvard CMT method, intermediate-period surface waves are included in the inversion for source parameters. The dispersion of teleseismic surface waves in the period range 40 to 150 sec is predicted by interpolation of recent global phase velocity maps. The method is tested on a set of 20 moderate and large (5.2 ≦ Mw ≦ 7.2) earthquakes with known mechanisms. The retrieved mechanisms are similar to the previous results, even when noise is added to the seismograms to simulate earthquakes of a smaller magnitude (Mw ∼ 4.5). The inversion algorithm is applied to the 1993 Klamath Falls mainshock and aftershock sequence, and the results compare well with earlier results. A catalog of Mw ≧ 4.5 focal mechanisms for Greece and surrounding areas for the first six months of 1995 is derived using the new method of analysis.
Magnitude of nonlinear sediment response in Los Angeles basin during the 1994 Northridge, California, earthquake
Authors: Beresnev Igor A. , Field Edward H. , Van Den Abeele Koen , Johnson Paul A. 
Published: September 2021

AbstractThe study of nonlinear site response has practical difficulties due to large ambiguities in isolating local response from other competing effects. We chose a sedimentary site LF6 in Los Angeles basin that (1) has the closest reference rock sites available, compared to other stations, allowing an accurate estimation of local amplification, and (2) illustrates clear resonance in the near surface. In our opinion, this case represents the least ambiguity in the identification of possible nonlinearity. The site responses during the Northridge, the 1987 Whittier Narrows events and the Northridge aftershocks are compared. The station shows a fundamental resonance-frequency change between the higher- and lower-amplitude motions in the entire ensemble of 17 events used. The net shear-modulus reduction during the Northridge event is a factor of 1.3 to 1.4 compared to the Whittier Narrows event and is a factor of 1.7 compared to the aftershocks. This result provides guidance of what to expect at other sites in the basin, where the nonlinear response is less easy to characterize.
Implications of a composite source model and seismic-wave attenuation for the observed simplicity of small earthquakes and reported duration of earthquake initiation phase
Authors: Singh S. K. , Ordaz M. , Mikumo T. , Pacheco J. , Valdés C. , Mandal P. 
Published: September 2021

AbstractAn examination of P waves recorded on near-source, velocity seismograms generally shows that most small earthquakes (Mw &lt; 2 to 3) are simple. On the other hand, larger earthquakes (Mw ≧ 4) are most often complex. The simplicity of the seismograms of Mw &lt; 2 to 3 events may reflect the simplicity of the source (and, hence, may imply that smaller and larger earthquakes are not self-similar) or may be a consequence of attenuation of seismic waves. To test whether the attenuation is the cause, we generated synthetic P-wave seismograms from a composite circular source model in which subevent rupture areas are assumed to follow a power-law distribution. The rupture of an event is assumed to initiate at a random point on the fault and to propagate with a uniform speed. As the rupture front reaches the center of a subevent patch (all of which are circular), a P pulse is radiated that is calculated from the kinematic source model of Sato and Hirasawa (1973). Synthetic P-wave seismograms, which are all complex, are then convolved with an attenuation operator for different values of t*. The results show that the observed simplicity of small events (Mw &lt; 2 to 3) may be entirely explained by attenuation if t* ≧ 0.02 sec.The composite source model predicts that the average time delay between the initiation of the rupture and the rupture of the largest patch, τ, scales as M01/3, such that log τ = (1/3) log M0 − 8.462. This relation is very similar to that reported by Umeda et al. (1996) between M0 and the observed time difference between the initiation of the rupture and the rupture of the “bright spot.” It roughly agrees with the relation between M0 and the duration of the initiation phase reported by Ellsworth and Beroza (1995) and Beroza and Ellsworth (1996). The relation also fits surprisingly well the data on duration of slow initial phase, tsip, and M0, reported by Iio (1995). One possible explanation of this agreement may be that the composite source model, which is essentially the “cascade” model, successfully captures the evolution of the earthquake source process and that the rupture initiation and the abrupt increase in the velocity amplitude observed on seismograms by previous researchers roughly corresponds to the rupture of the first subevent and the breaking of the largest subevent in the composite source model.