bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismicity in the Rangely, Colorado, area: 1962-1970
Authors: Gibbs James F. , Healy John H. , Raleigh C. Barry , Coakley John 
Published: September 2021

abstract
Seismic data recorded for a 7-year period at the Uinta Basin Observatory were searched for earthquakes originating near an oil field at Rangely, Colorado, 65 km ESE of the observatory. Changes in the number of earthquakes recorded per year appear to correlate with changes in the quantity of fluid injected per year. Between November 1962 and January 1970, 976 earthquakes were detected near the oil field by the UBO station; 320 earthquakes were larger than magnitude 1.
Richter local magnitudes are estimated from both S-wave and P-wave measurements; a method based on the duration of the seismic signal is used to estimate the magnitude of the larger shocks. Magnitude of the two largest shocks was 3.4 and 3.3. The total seismic energy released was 1017 ergs. During this same period, the energy used for water injection, measured at the wellhead, was 1021 ergs.
SH pulse in an elastic wedge
Authors: Abo-Zena A. M. , King Chi-Yu 
Published: September 2021

abstract
This paper gives an analysis of the response of an elastic wedge of arbitrary angle to an impulsive SH source applied on the wedge surface along a line parallel to the edge of the wedge. A two-dimensional time-dependent Green's function for SH waves is constructed from an integral-transform approach. The result is given in a closed form for the incident and the reflected pulses and in an integral form for the diffracted pulse from the edge. For the special case that the wedge angle is an integral fraction of π, the result is interpretable in terms of a finite set of image sources with no diffraction effect. Numerical examples are given for illustration.
Surface-wave propagation under initial tension or compression
Authors: Brunelle E. J. 
Published: September 2021

AbstractThe propagation of Rayleigh waves in a half-space and the propagation of Love waves in a welded layer and half-space are examined when initial tensile or compressive stresses are present. Using the perturbed and linearized equations of elasticity, which include the effects of initial stress, a modified Rayleigh equation and a modified Love equation are obtained. The solution of the equations shows a dramatic change in the phase speeds of the two wave types under initial tension or compression. Numerical results are presented.
S-wave attenuation in the crust in northern Greece
Authors: Hatzidimitriou P. M. 
Published: September 2021

AbstractThe attenuation of shear waves in the crust is estimated, for frequencies between 1.5 and 12.0 Hz, by applying a single-station method based on the rate of decay of the S-wave to coda-wave amplitude ratio with distance. The data used come from local earthquakes that occurred in the Thessaloniki area, northern Greece, during the period 1983 through 1989 and were recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. The Qs values obtained are 115, 244, 477, and 755 for 1.5, 3.0, 6.0, and 12.0 Hz, respectively. These values are very close to the coda Q values estimated for the same area using the S-to-S single scattering model for lapse times between 30 and 100 sec but they are higher than the coda Q values for lapse times between 10 and 30 sec. The estimated Qs is found to be strongly frequency dependent, proportional to f0.91, which is very close to the frequency dependence of the coda Q.
Sediment-induced amplification in the Northeastern United States: A case study in Providence, Rhode Island
Authors: Fischer Karen M. , Salvati Lynn A. , Hough Susan E. , Gonzalez Edward , Nelsen Chad E. , Roth Erich G. 
Published: September 2021

AbstractWe employed ambient-noise measurements to assess the potential for seismic site response in sediment-filled valleys that intersect beneath downtown Providence, Rhode Island. At eight valley stations and at two sites on an adjacent bedrock highland, we recorded ground motion from two types of sources: pile drivers at a local construction site and ambient microtremors. At all valley sites where sediment thicknesses exceed 10 m, spectral ratios contain amplitude peaks at frequencies of 1.5 to 3.0 Hz. In contrast, spectral ratios from the two sites on the bedrock highland where sediment cover is less than 4-m thick are relatively flat within this frequency range. A variety of borehole logs identified two fundamental sediment types (soft sediment and a consolidated glacial till) and were used to map layer thicknesses over the entire study region. Refraction data constrained P-wave velocity in the bedrock to be 3680 ± 160 m/sec and indicated two soft-sediment layers with P-wave velocities of 300 ± 50 and 1580 ± 120 m/sec. Using a one-dimensional reflection matrix technique, we matched the spectral-ratio peak observed at each valley site with the frequency of fundamental resonance predicted for local layer thicknesses and velocities. A positive correlation between the best-fitting soft-sediment velocities and bedrock depth may reflect greater compaction in the deepest sediments or a locally two-dimensional sediment resonance at the deepest sediment sites. We conclude that unconsolidated sediment layers under downtown Providence have the potential to amplify earthquake ground motion at frequencies damaging to engineered structures.
Scaling relations for strong ground motion prediction models with M2 terms
Authors: Fukushima Yoshimitsu 
Published: September 2021

Abstract
In most previous studies on the attenuation relation of strong ground motion, the increase in amplitude with earthquake magnitude was expressed by a linear relation. However, if the ω−2 source model is assumed, the corner period of the spectrum varies with the magnitude, and the scaling law of the source spectrum amplitude becomes a complicated function of magnitude. The scaling relation of the spectrum amplitude with MW can be simply approximated as a quadratic function, and the coefficient of the MW2 term should be negative. On the contrary, positive coefficients of the ML2, mbLg2, and MJ2 (MJ: magnitude of Japan Meteorological Agency) terms have been derived by regression analyses of strong ground motions.
Based on the ω−2 model, semi-empirical relations between Mo and the magnitudes were derived. Further, the seismological scaling law of the source spectrum obtained from the relation between Mo and the magnitudes was approximated as a quadratic function of the magnitude, and positive coefficients of the squared magnitude terms were obtained. These results stem from the definitions of magnitude derived from amplitudes of seismograms around a specific period of 1.0 sec for ML and mbLg and of 5.0 sec for MJ.
P-wave backazimuth anomalies observed by a small-aperture seismic array at Pinyon Flat, southern California: Implications for structure and source location
Authors: Lin Cheng-Horng , Roecker S. W. 
Published: September 2021

AbstractSeismograms of earthquakes and explosions recorded at local, regional, and teleseismic distances by a small-aperture, dense seismic array located on Pinyon Flat, in southern California, reveal large (±15°) backazimuth anomalies. We investigate the causes and implications of these anomalies by first comparing the effectiveness of estimating backazimuth with an array using three different techniques: the broadband frequency-wavenumber (BBFK) technique, the polarization technique, and the beamforming technique. While each technique provided nearly the same direction as a most likely estimate, the beamforming estimate was associated with the smallest uncertainties. Backazimuth anomalies were then calculated for the entire data set by comparing the results from beamforming with backazimuths derived from earthquake locations reported by the Anza and Caltech seismic networks and the Preliminary Determination of Epicenters (PDE) Bulletin. These backazimuth anomalies have a simple sinelike dependence on azimuth, with the largest anomalies observed from the southeast and northwest directions. Such a trend may be explained as the effect of one or more interfaces dipping to the northeast beneath the array. A best-fit model of a single interface has a dip and strike of 20° and 315°, respectively, and a velocity contrast of 0.82 km/sec. Application of corrections computed from this simple model to ray directions significantly improves locations at all distances and directions, suggesting that this is an upper crustal feature. We confirm that knowledge of local structure can be very important for earthquake location by an array but also show that corrections computed from simple models may not only be adequate but superior to those determined by raytracing through smoothed laterally varying models.
Rupture directivity and slip distribution of theM4.3 foreshock to the 1992 Joshua Tree earthquake, Southern California
Authors: Mori Jim 
Published: September 2021

AbstractDetails of the M 4.3 foreshock to the Joshua Tree earthquake were studied using P waves recorded on the Southern California Seismic Network and the Anza network. Deconvolution, using an M 2.4 event as an empirical Green's function, corrected for complicated path and site effects in the seismograms and produced simple far-field displacement pulses that were inverted for a slip distribution. Both possible fault planes, north-south and east-west, for the focal mechanism were tested by a least-squares inversion procedure with a range of rupture velocities. The results showed that the foreshock ruptured the north-south plane, similar to the mainshock. The foreshock initiated a few hundred meters south of the mainshock and ruptured to the north, toward the mainshock hypocenter. The mainshock (M 6.1) initiated near the northern edge of the foreshock rupture 2 hr later. The foreshock had a high stress drop (320 to 800 bars) and broke a small portion of the fault adjacent to the mainshock but was not able to immediately initiate the mainshock rupture.
Comparison of magnitudes estimated by the Japan Meteorological Agency with moment magnitudes for intermediate and deep earthquakes
Authors: Katsumata Akio 
Published: September 2021

Abstract
The magnitude, MJMA, estimated by the Japan Meteorological Agency (JMA) is generally referred to in Japan for the regional seismicity in the area. MJMA is determined from maximum displacement amplitudes of the total seismic wave traces. For earthquakes shallower than 60 km, MJMA is determined by Tsuboi's formula, and for earthquakes deeper than 60 km, by Katsumata's formula. These relations were designed to give almost the same magnitude value as that of Gutenberg and Richter. We compared MJMA with moment magnitude, MW, which can be calculated from the centroid moment tensor (CMT) solutions. It was found that the average difference between MJMA and MW is not significant for shallow earthquakes in the magnitude range from 5 to 7, but it is significant at a low level for the earthquakes of deeper foci. The averaged difference reaches about 0.4 magnitude units for the focal depth of 600 km. We derived an attenuation function for the maximum displacement amplitude assuming the validity of the moment magnitude. This relation between epicentral distance and amplitude for shallow earthquakes is almost identical to the one calculated from Tsuboi's formula. It is suggested that the estimated attenuation function for deep-focus earthquakes reflects the specific Q and velocity structure that is peculiar to the subduction zone.
Shear-wave velocity of the sedimentary basin in the upper Mississippi embayment usingS-to-Pconverted waves
Authors: Chen Kou-Cheng , Chiu Jer-Ming , Yang Yung-Tun 
Published: September 2021

AbstractFrom mid-October 1989 to August 1992, 40 three-component PANDA (Portable Array for Numerical Data Acquisition) stations were deployed in the central New Madrid seismic zone. Three-component digital seismograms recorded by the PANDA stations in the region are characterized by (1) the very weak direct S arrivals on the vertical component, which can be identified unambiguously from the two horizontal components, and (2) at least two prominent secondary arrivals between the direct P and S arrivals, one (Sp) dominant on the vertical component and another (Ps) with smaller amplitude on the two horizontal components. Travel-time differences between the Sp and S and between the P and Ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event. Polarization analyses of three-component seismograms and travel-time measurements confirm the interpretation that these two secondary arrivals are the P-to-S (Ps) and S-to-P (Sp) converted waves that occur at the bottom of the sedimentary basin beneath each station. Since abundant well-log data are available in the upper Mississippi embayment, the thickness of the sediments beneath each seismic station can be estimated. Travel-time differences between the direct and the converted waves can be used to calculate average shear-wave velocity for the sediments beneath each station. The estimated shear-wave velocities of the sediments beneath PANDA stations vary from 0.45 to 0.67 km/sec. The higher shear-wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden.
Earthquake mechanisms from linear-programming inversion of seismic-wave amplitude ratios
Authors: Julian Bruce R. , Foulger G. R. 
Published: September 2021

AbstractThe amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first-motion polarities, but amplitudes are severely distorted by the effects of heterogeneity in the Earth. This distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases, rather than simple amplitudes, but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal. Searching methods are particularly costly if general (moment tensor) mechanisms are allowed. Efficient linear-programming methods, which do not suffer from these problems, have previously been applied to inverting polarities and wave amplitudes. We extend these methods to amplitude ratios, in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation. Three-component digital data for an earthquake at the Hengill-Grensdalur geothermal area in southwestern Iceland illustrate the power of the method. Polarities of P, SH, and SV waves, unusually well distributed on the focal sphere, cannot distinguish between diverse mechanisms, including a double couple. Amplitude ratios, on the other hand, clearly rule out the double-couple solution and require a large explosive isotropic component.
Numerical simulations of wave propagation in heterogeneous wave guides with implications for regional wave propagation and the nature of lithospheric heterogeneity
Authors: Wagner Gregory S. 
Published: September 2021

AbstractI present results from elastic finite-difference simulations of regional wave propagation conducted in an effort to characterize, in a statistical sense, the nature of lithospheric heterogeneities required to generate scattered wave fields with characteristics consistent with those observed in regional array data. In particular, regional P, S, and Lg wave trains that are comprised not of the occasional coherent deterministic phase emersed in randomly scattered coda, but of a continuous succession of coherent forward-scattered arrivals. My modeling suggests that lithospheric heterogeneities should be parameterized using spatially anisotropic correlation functions. Models containing spatially isotropic heterogeneities inhibit the extent to which energy is forward scattered and trapped in the crustal wave guide and, consequently, produce regional wave fields whose characteristics are inconsistent with array observations. Models containing spatially anisotropic heterogeneities—which preferentially forward scatter energy that is subsequently trapped in the crustal wave guide—produce wave fields whose characteristics are consistent with regional array observations and provide intuitively appealing representations of subsurface structure.
Source characteristics of small to moderate earthquakes in the Kanto region, Japan: application of a new definition of theS-wave time window length
Authors: Watanabe Kazutoshi , Sato Haruo , Kinoshita Shigeo , Ohtake Masakazu 
Published: September 2021

AbstractThe S wave from a local earthquake generally consists of several pulses, in contrast to a simple pulse of P wave. This results in a large uncertainty in the estimation of seismic moment and wave energy when the window length for S-wave analysis is not chosen properly. In this study, we propose a new method to define objectively an appropriate time window length of the S wave for estimation of source characteristics based on the S-wave to P-wave energy ratio for a point shear dislocation source. Analyzing waveform data of 97 local earthquakes in the Kanto region, Japan, whose magnitudes M range from 3.3 to 6.0, we obtained simple equations for predicting the time window length of the S-wave TS as a function of earthquake magnitude or pulse width of P-wave TP; we got TS ≈ 1.8 TP for the relation between TP and TS. Applying the S-wave window thus defined, we estimated seismic energy E, seismic moment M0, and corner frequency fc for both P and S waves. Regression analysis of those parameters revealed (1) our method to define TS is confirmed by the fact that the seismic moment determined from P and S waves are consistent; (2) in the range of 1014 &lt; M0 &lt; 1018 (N·m), M0 is almost proportional to f−3c both for P and S waves; (3) the value of E/M0 is 2.7 ∼ 4.0 × 10−5; and (4) breakdown of the scaling relation is seen at M ≦ 4.
Rocking and overturning of precariously balanced rocks by earthquakes
Authors: Shi Baoping , Anooshehpoor Abdolrasool , Zeng Yuehua , Brune James N. 
Published: September 2021

Abstract
Precariously balanced rocks in seismically active regions may be used to provide constraints on probabilistic estimates of strong ground motion. A computer program is developed to study the rocking response of models of precariously balanced rocks when subjected to various levels of ground accelerations. The computer code, validated by comparing the numerical and experimental results for simple-shaped rigid blocks, is used to study the rocking response of rectangular blocks with various aspect ratios to the El Centro strong ground motion recording of the 18 May 1940 Imperial Valley earthquake. Results show that during earthquakes, the horizontal components of ground motion play a dominant role in overturning rocking objects. The rederived and corrected Housner's equation (1963) could be used to estimate the minimum overturning acceleration of precarious rocks at different frequencies by measuring the quasi-static toppling acceleration in the field.
Shallow velocity structure and poisson's ratio at the Tarzana, California, strong-motion accelerometer site
Authors: Catchings R.  D. , Lee W.  H. K. 
Published: September 2021

Abstract
The 17 January 1994, Northridge, California, earthquake produced strong ground shaking at the Cedar Hills Nursery (referred to here as the Tarzana site) within the city of Tarzana, California, approximately 6 km from the epicenter of the mainshock. Although the Tarzana site is on a hill and is a rock site, accelerations of approximately 1.78 g horizontally and 1.2 g vertically at the Tarzana site are among the highest ever instrumentally recorded for an earthquake. To investigate possible site effects at the Tarzana site, we used explosive-source seismic refraction data to determine the shallow (&lt;70 m) P-and S-wave velocity structure. Our seismic velocity models for the Tarzana site indicate that the local velocity structure may have contributed significantly to the observed shaking. P-wave velocities range from 0.9 to 1.65 km/sec, and S-wave velocities range from 0.20 and 0.6 km/sec for the upper 70 m. We also found evidence for a local S-wave low-velocity zone (LVZ) beneath the top of the hill. The LVZ underlies a CDMG strong-motion recording site at depths between 25 and 60 m below ground surface (BGS). Our velocity model is consistent with the near-surface (&lt;30 m) P- and S-wave velocities and Poisson's ratios measured in a nearby (&lt;30 m) borehole. High Poisson's ratios (0.477 to 0.494) and S-wave attenuation within the LVZ suggest that the LVZ may be composed of highly saturated shales of the Modelo Formation. Because the lateral dimensions of the LVZ approximately correspond to the areas of strongest shaking, we suggest that the highly saturated zone may have contributed to localized strong shaking. Rock sites are generally considered to be ideal locations for site response in urban areas; however, localized, highly saturated rock sites may be a hazard in urban areas that requires further investigation.
Is the quiescence of major earthquakes (M ≧ 7.5) Since 1952 in the Himalaya and northeast India real?
Authors: Satyabala S.  P. , Gupta Harsh  K. 
Published: September 2021

Abstract
The earthquake catalog for the Himalaya and the northeast India regions (latitude 20°N to 38°N and longitude 75°E to 100°E, comprising of portions of the Himalaya and Arakan Yoma fold belt) for the period 1897 to May 1995 shows that there have been 14 major earthquakes (M ≧ 7.5) during the period 1897 to 1952 and no major earthquakes after 1952. To investigate the possibility that this quiescence is an artifact of nonuniform magnitude scales over the period of study, we examined three global catalogs and found that there is indeed an absence of major earthquakes after 1952.
Source complexity of the 1994 Northridge earthquake and its relation to aftershock mechanisms
Authors: Thio Hong Kie , Kanamori Hiroo 
Published: September 2021

Abstract
We determined the source process of the 1994 Northridge earthquake in relation to the aftershock mechanisms. To study the source complexity of the mainshock, we inverted the P and SH waveforms recorded by the IRIS and IDA/IRIS networks, using the method of Kikuchi and Kanamori (1991) in which the rupture is represented by a series of discrete subevents with varying mechanisms. The waveforms show that the rupture consisted of several subevents with about 2 sec in between. Our solution consists of three subevents with essentially the same mechanism, viz., strike, dip, and slip of 130°, 42°, and 116°, respectively. The first subevent occurred at a depth of about 19 km, followed after 2 sec by the second and largest subevent at a depth of 17 km and the third subevent again 2 sec after the second at a depth of about 13 km. The total moment from the body waves of this sequence is about 1.1 × 1026 dyne · cm (Mw = 6.6) with a source duration of 7 sec.
The large depths of these subevents explain the lack of any surface rupture. Furthermore, the upward propagation of the subevents is consistent with the depth of the hypocenter and the distribution of the aftershocks, which are shallower and more northerly than the mainshock hypocenter.
The aftershocks were analyzed using data from the TERRAscope network. We inverted short-period surface waves to determine the moment tensor for 70 events with Mw &gt; 3.5. The aftershocks can be grouped into three regions based on the mechanisms: the eastern part of the aftershock zone, where we find thrust events with mechanisms very similar to the main event; a central area with predominantly strike-slip events; and an area to the west, where we find oblique thrust events but with more northerly P axes than in the eastern region. This distribution suggests that the fault system on which the Northridge earthquake occurred is segmented and that the extent of the Northridge rupture is controlled by a change in geometry of the fault. We find a high stress drop (270 bar) for the mainshock; we propose that the changes in the fault geometry prevented a slip pulse from propagating, thereby causing a high ratio of slip-to-rupture length.