bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake
Authors: Wald David J. , Heaton Thomas H. 
Published: September 2021

AbstractWe have determined a source rupture model for the 1992 Landers earthquake (MW 7.2) compatible with multiple data sets, spanning a frequency range from zero to 0.5 Hz. Geodetic survey displacements, near-field and regional strong motions, broadband teleseismic waveforms, and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface. Our fault parameterization involves a variable-slip, multiple-segment, finite-fault model which treats the diverse data sets in a self-consistent manner, allowing them to be inverted both independently and in unison. The high-quality data available for the Landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern. In all models, consistent features include the following: (1) similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 × 1026 dyne-cm (seismic potency of 2.3 to 2.7 km3); (2) very heterogeneous, unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km, though slip is limited to shallower regions in some areas; (3) a total rupture duration of 24 sec and an average rupture velocity of 2.7 km/sec; and (4) substantial variations of slip with depth relative to measured surface offsets. The extended rupture length and duration of the Landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter-duration, strike-slip events. Our imaging allows visualization of the rupture evolution, including local differences in slip durations and variations in rupture velocity. Rupture velocity decreases markedly at shallow depths, as well as near regions of slip transfer from one fault segment to the next, as rupture propagates northwestward along the multiply segmented fault length. The rupture front slows as it reaches the northern limit of the Johnson Valley/Landers faults where slip is transferred to the southern Homestead Valley fault; an abrupt acceleration is apparent following the transfer. This process is repeated, and is more pronounced, as slip is again passed from the northern Homestead Valley fault to the Emerson fault. Although the largest surface offsets were observed at the northern end of the rupture, our modeling indicates that substantial rupture was also relatively shallow (less than 10 km) in this region.
Investigation of the rupture process of the 28 June 1992 Landers earthquake utilizing TERRAscope
Authors: Dreger Douglas S. 
Published: September 2021

Abstract
Displacement seismograms recorded by TERRAscope for the 28 June 1992 Landers earthquake (MW 7.3) are deterministically modeled using a forward, point-source summation technique. Although the data set is sparse, it was possible to robustly determine important rupture parameters such as gross slip distribution, rupture velocity, rise time, and total source duration. The relatively simple approach lends itself to rapid application following large earthquakes, provided that a catalog of Green's functions appropriate for the region is available.
The fault used in the modeling of the Landers mainshock has a length of 70 km along strike and a width of 15 km along dip. A model was found in which the distribution and amplitude of slip at the surface matches the observed surface slip and provides a very good level of fit to the seismic data. Seismically, the Landers earthquake is characterized as two subevents. The peak slip of the first subevent is 10 km north of the epicenter and the second is 40 km northwest along strike from the epicenter. The seismic moment is distributed as 2 × 1026 dyne-cm to the first and 6 × 1026 to the second subevent, respectively. It was assumed in our modeling that the distribution of seismic moment along strike was the same at all depths. This assumption implies that slip at depth is 69% of that at the surface as a result of differences in the material properties in the velocity model. the sensitivities of the source model to rupture velocity and dislocation rise time were examined. A rupture velocity of 2.9 km/sec (80% of the shear-wave velocity) and a rise time of 1 to 3 sec were found to satisfy the data. The rise time is only a fraction of the total source process time of 24 sec, and implies that slip on the fault occurred within a narrow band (3 to 10 km), at any instant during the rupture.
Magnetic field observations in the near-field the 28 June 1992 Mw 7.3 Landers, California, earthquake
Authors: Johnston M. J. S. , Mueller R. J. , Sasai Y. 
Published: September 2021

Abstract
Recent reports suggest that large magnetic field changes occur prior to, and during, large earthquakes. Two continuously operating proton magnetometers, LSBM and OCHM, at distances of 17.3 and 24.2 km, respectively, from the epicenter of the 28 June 1992 Mw 7.3 Landers earthquake, recorded data through the earthquake and its aftershocks. These two stations are part of a differentially connected array of proton magnetometers that has been operated along the San Andreas fault since 1976. The instruments have a sensitivity of 0.25 nT or better and transmit data every 10 min through the GOES satellite to the USGS headquarters in Menlo Park, California. Seismomagnetic offsets of −1.2 ± 0.6 and −0.7 ± 0.7 nT were observed at these sites. In comparison, offsets of −0.3 ± 0.2 and −1.3 ± 0.2 nT were observed during the 8 July 1986 ML 5.9 North Palm Springs earthquake, which occurred directly beneath the OCHM magnetometer site. The observations are generally consistent with seismomagnetic models of the earthquake, in which fault geometry and slip have the same from as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake. In these models, right-lateral rupture occurs on connected fault segments in a homogeneous medium with average magnetization of 2 A/m. The fault-slip distribution has roughly the same form as the observed surface rupture, and the total moment release is 1.1 × 1020 Nm. There is no indication of diffusion-like character to the magnetic field offsets that might indicate these effects result from fluid flow phenomena. It thus seems unlikely that these earthquake-generated offsets and those produced by the North Palm Springs earthquake were generated by electrokinetic effects. Also, there are no indications of enhanced low-frequency magnetic noise before the earthquake at frequencies below 0.001 Hz.
Regional observation of a nuclear test from a vertical hydrophone array
Authors: Harris D. B. , D'Spain G. , Goldner A. 
Published: September 2021

AbstractIn order to evaluate the potential of water-column vertical hydrophone arrays for the measurement of continental events at regional distances, ocean acoustic data bases were examined for arrivals from these types of events. In 1987, the nuclear test LOCKNEY (mb 5.7, 37.28°N 116.38°W) was observed in the deep-ocean water column at a range of 900 km by the Vertical Line Array (VLA) at 35° N 126° W. Although the hydrophone data were contaminated below 10 Hz by array suspension noise and ocean acoustic noise, adaptive array processing allows us to extract the P and T phases. The root-mean-square (rms) direct P-wave amplitude in the water column is 100.6 dB referenced to 1 μPa in the 4- to 8-Hz band in a 20-sec window, which suggests a detection threshold of mb 5.2 in a deep oceanic environment at this range for a single hydrophone. The arrival time of the T phase [i.e., the portion of seismic energy that has somehow coupled into, and propagated within, the deep ocean sound channel (Aki and Richards, 1980)] is consistent with a P-wave conversion at the continental margin, assuming a velocity of 6 km/sec from NTS to the continental margin and acoustic propagation at 1.5 km/sec in the water column from the continent to the array.
A kinematic self-similar rupture process for earthquakes
Authors: Herrero A. , Bernard P. 
Published: September 2021

Abstract
The basic assumption that the self-similarity and the spectral law of the seismic body-wave radiation (e.g., ω-square model) must find their origin in some simple self-similar process during the seismic rupture led us to construct a kinematic, self-similar model of earthquakes. It is first assumed that the amplitude of the slip distribution high-pass filtered at high wavenumber does not depend on the size of the ruptured fault. This leads to the following “k-square” model for the slip spectrum, for k &gt; 1/L: Δ~uL(k)=CΔσμLk2,
where L is the ruptured fault dimension, k the radial wavenumber, Δσ the mean stress drop, μ the rigidity, and C an adimensional constant of the order of 1. The associated stress-drop spectrum, for k &gt; 1/L, is approximated by Δ~σL(k)=ΔσLk.
The rupture front is assumed to propagate on the fault plane with a constant velocity v, and the rise time function is assumed to be scale dependent. The partial slip associated to a given wavelength 1/k is assumed to be completed in a time 1/kv, based on simple dynamical considerations. We therefore considered a simple dislocation model (instantaneous slip at the final value), which indeed correctly reproduces this self-similar characteristic of the slip duration at any scale. For a simple rectangular fault with isochrones propagating in the x direction, the resulting far-field displacement spectrum is related to the slip spectrum as u˜(ω)=FΔ~u(kx=1Cdωv,ky=0),
where the factor F includes radiation pattern and distance effect, and Cd is the classical directivity coefficient 1/[1 − v/c cos (θ)]. The k-square model for the slip thus leads to the ω-square model, with the assumptions above. Independently of the adequacy of these assumptions, which should be tested with dynamic numerical models, such a kinematic model has several important applications. It may indeed be used for generating realistic synthetics at any frequency, including body waves, surface waves, and near-field terms, even for sites close to the fault, which is often of particular importance; it also provides some clues for estimating the weighting factors for the empirical Green's function methods. Finally, the slip spectrum may easily be modified in order to model other power-law decay of the radiation spectra, as well as composite earthquakes.
Observations of ambient noise and signal coherency on the Island of Hawaii for teleseismic studies
Authors: Li Yingping , Prothero William , Thurber Clifford , Butler Rhett 
Published: September 2021

AbstractAmbient seismic noise conditions at several sites on the Island of Hawaii have been studied by analyzing noise power spectral density (PSD) and signal-to-noise ratio (SNR) of teleseisms. Broadband digital waveform data used in this study were collected during Project ALOHA. Direct comparison of noise PSD and SNR of teleseisms simultaneously recorded at stations on Hawaii and at station KIP on Oahu indicates that the stations on Hawaii are quieter than station KIP on Oahu in the frequency band of 0.1 to 1 Hz, suggesting that the Island of Hawaii can provide better noise conditions than station KIP. Our interpretation of this observation is that the area and volume of Hawaii are much larger than those of Oahu and distances to the coast for the stations on Hawaii are larger than that for station KIP on Oahu. Stronger attenuation and relatively low coherency for teleseismic signals on Hawaii in frequencies of 0.4 to 1.2 Hz are attributed to the presence of partial melt in the upper mantle. Teleseismic signal coherency is very low at frequencies above 2 Hz for a small array with a radius about 2 km. The relatively high coherency of the tangential component is strongly indicative of severe scattering effects caused by the heterogeneity in structure of the active volcanic area.
A multidisciplinary approach to seismic hazard in southern California
Authors: Ward Steven N. 
Published: September 2021

Abstract
A serious obstacle facing seismic hazard assessment in southern California has been the characterization of earthquake potential in areas far from known major faults where historical seismicity and paleoseismic data are sparse. This article attempts to fill the voids in earthquake statistics by generating “master model” maps of seismic hazard that blend information from geology, paleoseismology, space geodesy, observational seismology, and synthetic seismicity. The current model suggests that about 40% of the seismic moment release in southern California could occur in widely scattered areas away from the principal faults. As a result, over a 30-yr period, nearly all of the region from the Pacific Ocean to 50 km east of the San Andreas Fault has a greater than 50/50 chance of experiencing moderate shaking of 0.1 g or greater, and about a 1 in 20 chance of suffering levels exceeding 0.3 g. For most of the residents of southern California, thelion's share of hazard from moderate earthquake shaking over a 30-yr period derives from smaller, closer, more frequent earthquakes in the magnitude range (5 ≦ M ≦ 7) rather than from large San Andreas ruptures, whatever their likelihood.
The 1737 Calcutta earthquake and cyclone evaluated
Authors: Bilham Roger 
Published: September 2021

Abstract
Catalogs of historically devastating earthquakes (e.g., Dunbar et al., 1992) contain an entry for an earthquake in Calcutta in 1737 that is held responsible for the loss of 300,000 lives, thus rendering it one of the three most disastrous earthquakes in history. Yet, evidence for a severe earthquake is weak, consisting of anonymous reports conveyed to Europe 6 months later by merchant ships returning from Bengal. Official accounts of the disaster submitted to the East India Company headquarters in London list 3000 fatalities and omit mention of an earthquake. If the 11 October 1737 Calcutta earthquake is to remain on lists of catastrophic earthquakes, the following issues need to be resolved: the discrepancy between the 1737 urban population of Calcutta (&lt;20,000) and the number of claimed fatalities, the difficulty in distinguishing between damage from shaking and hurricane force winds and flooding that occurred during the same night, and the contradiction between the number of nocturnal deaths and the apparent earthquake resistance of hatched roof dwellings typical of eighteenth century rural Bengal. It is possible that earthquake damage may have been minimal or nonexistent.
Modeling viscoelastic waves: a comparison of ray theory and the finite-difference method
Authors: Quiroga-Goode Gerardo E. , Krebes E. S. , Le Lawrence H. T. 
Published: September 2021

AbstractTwo techniques for computing ray synthetic seismograms in anelastic media produce substantially different results in a model consisting of an elastic half-space overlying a stack of anelastic layers (Krebes and Slawinski, 1991). The first technique, the stationary ray method, involves an evaluation of the wave field integral by the method of steepest descent, and yields complex rays. In the second, the conventional ray method, it is assumed that the attenuation vector of the initial ray segment (in the elastic part of the model) is zero (which is not the case for the stationary ray). The essential difference between these two methods is that the stationary ray method gives minimum travel-time rays, thus agreeing with Fermat's principle. Krebes and Slawinski (1991) relied upon this fact to suggest that the stationary ray method is the correct method. However, since the method raises some conceptual peculiarities (e.g., the initial ray segment of the stationary ray is an inhomogeneous elastic wave propagating as a body wave), it is important to verify their results and conclusions with an independent solution of the problem; we use a numerical finite-difference solution. By making direct comparisons between synthetic seismograms obtained with the stationary ray method, conventional ray method, and finite differences, we find that the stationary ray method agrees with the finite-difference solution better than the conventional ray method.
Integral equation method for plane crack with arbitrary shape in 3D elastic medium
Authors: Fukuyama Eiichi , Madariaga Raul 
Published: September 2021

AbstractWe have derived stress integral equations for an arbitrary shaped plane crack in a three-dimensional (3D) infinite homogeneous isotropic elastic medium. First we obtained the integral equation for static crack, which is consistent with previous works. Then we derived a new boundary integral equation for the study of dynamic tensile and shear cracks. We removed the hypersingularity that appears in the usual formulation of the stress-boundary integral equation method by a regularization technique. The dynamic stress integral equation consists of three terms which can be physically explained. The first term is a modification of the static solution, the second one represents the diffraction of waves at slip discontinuities, and the last term is related to the effect of an instantaneous change in slip velocity. The first term controls the overall shape of the stress drop inside the crack. This term is important when we consider the final stress drop on the fault. However, the second and the third terms are dominant at a moving crack tip, and are responsible for the radiation of P and S waves. They are also very important for the application of a fracture criterion at the rupture front. Using this boundary integral equation we have calculated several numerical examples for both the static and dynamic fault models.
Analysis of broadband records from the 28 June 1992 Big Bear earthquake: Evidence of a multiple-event source
Authors: Jones Laura E. , Hough Susan E. 
Published: September 2021

AbstractThe 28 June 1992 Big Bear earthquake occurred at 15:05:21 GMT and is considered to be an aftershock of the earlier Mw = 7.3 Landers earthquake. From overall aftershock locations and long-period focal studies, rupture is generally assumed to have propagated northeast. No surface rupture was found, however, and the mainshock locations determined from both strong motion and TERRAscope data are mutually consistent and do not lie on the assumed fault plane. Further, directivity analysis of records from the TERRAscope array suggests significant short- and long-period energy propagating northwest along the presumed antithetic fault plane. This observation is supported by significant early aftershocks distributed along both the presumed rupture plane and the antithetic plane to the northwest. An empirical Green's function (eGf) approach using both the Mw = 5.2, 28 June 1992 14:43 GMT foreshock and the Mw = 5.0 17 August 1992 aftershock produces consistent results and suggests that the Big Bear event comprised at least two substantial subevents. From the eGf results, we infer that the second and possibly a third subevent occurred on the presumed (northeast striking) mainshock rupture surface, but that significant moment release occurred on the antithetic northwest striking surface. We present results from line-source fault modeling of broadband displacement recordings of the Big Bear mainshock, which indicate that a two-fault event is necessary to produce the observed waveforms. The limitations imposed by the mainshock location and directivity analysis require that the initial rupture be towards the northwest, striking 320°. This was followed approximately 4 sec later by bilateral rupture along a northeast-southwest fault that strikes 50° east of north.
Magnitude-dependent variance of peak ground acceleration
Authors: Youngs R. R. , Abrahamson N. , Makdisi F. I. , Sadigh K. 
Published: September 2021

AbstractWe examine the variability of peak horizontal and vertical accelerations of the large California strong-motion data set for the time period 1957 to 1991 and find a statistically significant dependence of the standard error on earthquake magnitude. Specifically, the standard error decreases with increasing magnitude. The analysis was conducted using a rigorous methodology that examines both earthquake to earthquake (inter-event) variability and within earthquake (intra-event) variability. The magnitude dependence is stronger for inter-event variability than intra-event variability, and stronger for horizontal peak acceleration than for vertical peak acceleration. The data from the recent Landers, Big Bear, and Northridge earthquakes are consistent with these results.
Source characterization and fault plane determination for MbLg = 1.2 to 4.4 earthquakes in the Charlevoix Seismic Zone, Quebec, Canada
Authors: Li Yingping , Doll Charles , Toksöz M. N. 
Published: September 2021

Abstract
Two earthquake doublets and two multiplets recorded by the Charlevoix Telemetered Network (CLTN) in the Charlevoix Seismic Zone (CSZ) of southern Quebec, Canada, have been analyzed using an empirical Green's function (EGF) method to derive the relative source time functions (RSTF's) of seven master events with MbLg = 1.2 to 4.4. We identified the doublets and multiplets using a waveform cross-correlation and relative event location technique to verify that each earthquake pair had similar focal mechanisms and hypocentral locations. Three-component S waveforms recorded by the high dynamic range (126 dB) instrumentation of the CLTN were used to extract the RSTF's.
The RSTF's reveal that six of the seven events are simple with single-source pulses having durations of 0.05 to 0.2 sec. Another earthquake (920310-0545, M 3.3) appears to be a double event with two episodes of rupturing. Azimuthal variations of the RSTF pulse amplitudes and widths provide strong evidence for the rupture directivities of five of the earthquakes (M = 1.2 to 4.4). The azimuthal variations in the RSTF pulse amplitudes were used to estimate the rupture directions and rupture velocities. Lower-bound estimates of the rupture velocity range from 0.5 to 0.7 Vs. Estimates of the rupture direction were combined with P-wave focal mechanisms for the four largest events (M 3.3 to 4.4) to identify the fault plane for these earthquakes. Source parameters were measured for the RSTF's of the master events, including seismic moments of 3.5 × 1018 to 5.3 × 1021 dyne-cm, fault radii of 100 to 330 m, and static stress drops of 2 to 90 bars. The fault radii and stress-drop estimates for M &gt; 3 events agree well with estimates obtained by other researchers for M ∼ 3 to 4.5 earthquakes in the CSZ. We also observed apparent scaling between the stress drop and the earthquake size, which has been reported in other studies of stress drop in northeastern North America.
Configuring a seismographic network for optimal monitoring of fault lines and multiple sources
Authors: Steinberg David M. , Rabinowitz Nitzan , Shimshoni Yair , Mizrachi Daphna 
Published: September 2021

AbstractThe geometric configuration of a seismographic network has important consequences for the ability to determine hypocenters with high precision. We present a method for optimal configuration when the network must monitor a system of faults. Our optimality criterion is drawn from the statistical theory of experimental design and can be effeciently maximized using an extension of the DETMAX algorithm. Our work generalizes that of Rabinowitz and Steinberg (1990), which treated the problem of optimal network configuration for monitoring a point source.