Abstract A least-squares point-by-point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history 1979 Imperial Valley, California, earthquake. The represented by a plane embedded in half-space where elastic properties vary with depth. yields both spatial temporal variations dislocation on for right-lateral strike-slip normal dip-slip components motion. Inversions are run different dips constant variable velocity models. Effects data sets also...

A method is presented for modeling earthquake strong ground motion, which uses the aftershocks associated with a large as Green's functions. major earthquake, rupture surface, modeled by collection of point sources distributed over fault plane. The response each source approximated motion closest aftershock. By using aftershock responses, effects true earth structure are included in process. This used to model El Centro displacement record 1940 Imperial Valley earthquake.

We have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses recorded strong ground motion and teleseismic waveforms. Well-located hypocenters are projected onto main shock fault plane, their positions examined relative zones displacement indicated by estimated slip. also examine focal mechanisms, when these data available, in an attempt identify possible secondary faulting within...

Abstract This article compares techniques for calculating broadband time histories of ground motion in the near field a finite fault by comparing synthetics with strong-motion data set 1994 Northridge earthquake. Based on this comparison, preferred methodology is presented. Ground-motion-simulation are divided into two general methods: kinematic- and composite-fault models. Green's functions three types evaluated: stochastic, empirical, theoretical. A hybrid scheme found to give best fit...

Abstract Near-source strong motion velocity records and teleseismic short-period P waveforms are modeled to obtain the spatial temporal distribution of slip for 1984 Morgan Hill earthquake. Both forward modeling constrained, least-squares inversion techniques used interpret in frequency range approximately 0.2 2.0 Hz. These data support a nearly unilateral rupture southeast with propagation nine-tenths local S-wave velocity. The majority occurs over fault length 25 km first approximation can...

We present a new method for calculating broadband time histories of ground motion based on hybrid low-frequency/high-frequency approach with correlated source parameters. Using finite-difference we calculate low- frequency synthetics (< ∼1 Hz) in 3D velocity structure. also compute 1D model using frequency-wavenumber method. The low frequencies from the calculation are combined high by matched filtering at crossover 1 Hz. description, common to both and synthetics, is random distributions...

This study examines the rationale of Hilbert-Huang transform (HHT) for analyzing dynamic and earthquake motion recordings in studies seismology engineering. In particular, this paper first provides fundamentals HHT method, which consist empirical mode decomposition (EMD) Hilbert spectral analysis. It then uses to analyze hypothetical real wave motion, results are compared with obtained by Fourier data processing technique. The analysis two indicates that method is able extract some...

Abstract We have inverted the teleseismic P waveforms recorded by stations of Global Digital Seismograph Network for 8 July 1986 North Palm Springs, California, 28 October 1983 Borah Peak, Idaho, and 19 September 1985 Michoacan, Mexico, earthquakes to recover distribution slip on each faults using a point-by-point inversion method with smoothing positivity constraints. In procedure, fault plane fixed strike dip is placed in region earthquake hypocenter divided into large number subfaults....

Large subduction earthquakes on the Cascadia zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being subducted beneath North America at rate of approximately 4 centimeters per year. The shares many characteristics with zones in southern Chile, southwestern Japan, and Colombia, where comparably also subducting. large earthquakes, ranging energy magnitude (M(w)) between 8 9.5, have occurred along these other zones. If storing elastic energy,...

A hybrid global search algorithm is used to solve the nonlinear problem of calculating slip amplitude, rake, risetime, and rupture time on a finite fault. Thirty‐five strong motion velocity records are inverted by this method over frequency band from 0.1 1.0 Hz for Northridge earthquake. Four regions larger‐amplitude identified: one near hypocenter at depth 17 km, second west about same depth, third updip 10 fourth northwest. The results further show an initial fast with 2.8 3.0 km/s...

Abstract We examined short-period P waves to investigate if waveform data could be used determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. removed path and site complications by choosing aftershock 2.7) as an empirical Green function. The main shock were deconvolved using function produce simple far-field displacement pulses. least-squares method invert these pulses slip distribution on finite fault. Both (strike 125°, dip...

Abstract Following the 1989 Loma Prieta earthquake, a dense array of seven digitally recorded, three-component seismograph stations was deployed on Robinwood Ridge 7.3 km northwest epicenter. The purpose this to investigate cause high levels structural damage and ground cracking observed ridge crest. Aftershocks recorded by allow comparison motion up slope from base data present an extremely complicated pattern that demonstrates importance three-dimensionality problem. Slowness analysis P...

The July 8, 1986, North Palm Springs earthquake is used as a basis for comparison of several different approaches to the solution rupture history finite fault. inversion waveform data considered; both teleseismic P waveforms and local strong ground motion records. Linear parametrizations slip amplitude are compared with nonlinear time. Inversions using synthetic empirical Green's functions considered. In general, accurate more readily calculable problem where simple ray theory flat‐layered...

abstract Near-source ground motion at four azimuths but constant epicentral range is computed from a buried circular strike-slip fault in half-space. Particle acceleration, velocity, and displacement each station on the free surface frequency band 0.0 to 5.0 Hz. The assumed dislocation derived Kostrov (1964) function for continuously propagating stress relaxation. azimuthal variations amplitudes waveforms directly result spatially varying slip fault, radiation pattern over magnitude...

Twelve three-component strong-motion displacement records are modeled for the 1979 Imperial Valley earthquake to recover distribution of slip on fault plane. The final model, which point source responses calculated by a discrete wavenumber/finite element technique, uses structure with gradients in material properties rather than layers. effects velocity gradient investigated comparing synthetics layer-over-a-half-space model using generalized rays. It is shown that uniform rupture...

Abstract We simultaneously invert the strong-motion velocity records and long- intermediate-period teleseismic P waveforms of 19 September 1985 Michoacan, Mexico, earthquake to recover distribution slip on fault using a point-by-point constrained stabilized, least-squares inversion method. A plane with strike fixed at 300° dip 14° is placed in region hypocenter divided into 120 subfaults. Rupture assumed propagate 2.6 km/sec away from hypocenter. Synthetic near-source ground motions for pure...

Abstract We estimate stress drops for earthquakes in and near the continental United States using method of spectral ratios. The ratio acceleration spectra between collocated recorded at a given station removes effects path recording site yields source parameters including corner frequency for, seismic moment between, two earthquakes. determine drop from these 1121 greater than M ∼3 60 earthquake clusters. find that average Brune few eastern (EUS) tectonic mainshocks studied (2.6–36 MPa) is...

Abstract Ground-motion records from aftershocks of the 1994 Northridge earthquake are used to estimate site response in urban Los Angeles area. Over 1300 shear-wave 61 sources and 90 sites a linear inversion for source site-response spectra. The methodology makes no assumptions about shape spectrum. To obtain stable unique inverse, Q model geometrical spreading factor assumed. In addition, at hard-rock is constrained be approximately 1.0 with kappa 0.02. spectra compare favorably results...

Abstract Aftershocks of the 1989 Loma Prieta, California, earthquake are used to estimate site response along San Francisco Peninsula. A total 215 shear-wave records from 24 sources and 21 sites in a linear inversion for source spectra. The methodology makes no assumptions about shape spectrum. However, obtain stable, unique inverse Q model geometrical spreading factor assumed, as well constraint on that sets averaged over two specific stations 1.0. Site responses calculated by this...

Mathematical models of soil nonlinearity in common use and recently developed nonlinear codes are compared to investigate the range their predictions. We consider equivalent linear formulations with without frequency-dependent moduli damping ratios for total effective stress. Average velocity profiles 150 m depth midrange National Earthquake Hazards Reduction Program site classifications (B, BC, C, D, E) top 30 used compare response a wide conditions from rock soft soil. Nonlinear using...

Abstract This article addresses the variability of site response in Los Angeles area and possible structural causes for observations. Aftershock records from 231 sites San Fernando basins surrounding mountains are used this study. Spectral ratios, taken with respect to a low-amplitude reference site, document variation amplification frequency range 2 6 Hz, both spatially backazimuth source. At higher frequencies (6 10 Hz), spectral ratios shown have greater spatial variability. Interstation...

Abstract Strong motion records of the 1989 Loma Prieta earthquake are inverted to determine a model rupture history. Uncorrected horizontal and vertical accelerograms integrated particle velocity time histories for 38 stations within an epicentral range 75 km. The bandpassed filtered with corners at 0.05 1.0 Hz. These using nonlinear method solve distribution slip amplitudes times specified locations on fault plane. plane is priori: km long 17 wide, extending from 3 19 depth constant dip...

Abstract Broadband, digital, teleseismic body waves ( P and SH) are inverted to obtain the history of slip for 17 October 1989, Loma Prieta earthquake. Comparison finite-fault, waveform, inversion results using an L 1 norm 2 reveal some basic uncertainties in rupture that not usually appreciated earthquake source studies. However, more robust features can be identified less dependent on choice minimization norm. From a consideration first-motion data forward modeling waves, strike dip our...

Abstract A pair of significant earthquakes occurred on conjugate faults in the western Imperial Valley involving through-going Superstition Hills fault and Elmore Ranch cross fault. The first event was located fault, Ms = 6.2, larger 6.6. latter is seen as a doublet teleseismically with amplitudes ratio 1:2 delayed by about 8 sec. This 8-sec delay also dozen strong-motion records. These records are used constrained least-squares inversion scheme to determine distribution slip 2-D Upon closer...

Broadband vertical P-wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in circum-Pacific last 45 yr. Most studied come a common instrument, Pasadena, California, Benioff 1-90 seismometer. Propagation and instrument effects deconvolved using damped least-squares inversion to obtain teleseismic source time function. The has additional constraint that function be positive everywhere. period band over functions considered reliable is 2.5 50...