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Paul Spudich

Publications and source records attributed to Paul Spudich.

9 recordsLinked to original sources
USGS2012

Source parameters of the 1980 Mammoth Lakes, California, earthquake sequence

From the more than 1500 Mammoth Lakes earthquakes recorded on three-component digital seismographs (Spudich et al., 1981), 150 were used in an analysis of the locations, mechanism, and source parameters. A composite fault plane solution of nine earthquakes 3.9 ≤ M ≤ 5.1 defines a right-lateral strike slip mechanism on a steeply dipping nearly east-west plane striking S75°E or left-lateral strike slip on a nearly north-south plane striking N10°E. Vertical cross sections of well-located aftershocks indicate possibly three east-west planes that coincide with the locations of the four largest earthquakes with M L ≥ 6.0. Using the spectral analysis of S waves (Brune, 1970), source parameters for 67 earthquakes were determined. Forty-eight had magnitudes greater than or equal to 3.0. Seismic moments ranged from 9.20×10 18 dyn cm to 2.33×10 24 dyn cm. Earthquakes with seismic moment greater than about 1.0×10 21 dyn cm had nearly constant stress drops (≃ 50 bars); earthquakes with seismic moment less than about 1.0×10 21 dyn cm had stress drops that apparently decrease as seismic moment decreases.

California↗
USGS2009

Software for inference of dynamic ground strains and rotations and their errors from short baseline array observations of ground motions

In two previous articles we presented a formulation for inferring the strains and rotations of the ground beneath a seismic array having a finite footprint. In this article we derive expressions for the error covariance matrices of the inferred strains and rotations, and we present software for the calculation of ground strains, rotations, and their variances from short baseline array ground-motion data.

Bulletin of the Seismological Society of America↗
USGS2004

A formulation of directivity for earthquake sources using isochrone theory

A functional form for directivity effects can be derived from isochrone theory, in which the measure of the directivity-induced amplification of an S body wave is c, the isochrone velocity. Ground displacement of the near-, intermediate-, and far-field terms of P and S waves is linear in isochrone velocity for a finite source in a whole space. We have developed an approximation c-tilde-prime of isochrone velocity that can easily be implemented as a predictor of directivity effects in empirical ground motion prediction relations. Typically, for a given fault surface, hypocenter, and site geometry, c-tilde-prime is a simple function of the hypocentral distance, the rupture distance, the crustal shear wave speed in the seismogenic zone, and the rupture velocity. c-tilde-prime typically ranges in the interval 0.44, for rupture away from the station, to about 4, for rupture toward the station. In this version of the theory directivity is independent of period. Additionally, we have created another functional form which is c-tilde-prime modified to include the approximate radiation pattern of a finite fault having a given rake. This functional form can be used to model the spatial variations of fault-parallel and fault-normal horizontal ground motions. The strengths of this formulation are 1) the proposed functional form is based on theory, 2) the predictor is unambiguously defined for all possible site locations and source rakes, and 3) it can easily be implemented for well-studied important previous earthquakes. We compare predictions of our functional form with synthetic ground motions calculated for finite strike-slip and dip-slip faults in the magnitude range 6.5 - 7.5. In general our functional form correlates best with computed fault-normal and fault-parallel motions in the synthetic motions calculated for events with M6.5. Correlation degrades but is still useful for larger events and for the geometric average horizontal motions. We have had limited success applying it to geometrically complicated faults.

Open-File Report↗
USGS2003

Additional information for “TREMOR: A Wireless, MEMS Accelerograph for Dense Arrays” (Evans et al., 2003)

The length of Evans et al. (2003) necessitated transfer of several less germane sections to this alternate forum to meet that venue’s needs. These sections include a description of the development of Figure 1, the plot of spatial variability so critical to the argument for dense arrays of strong-motion instruments; the description of the rapid, integer, computational method for PGV used in the TREMOR instrument (the Oakland instrument, the commercial prototype, and the commercial instrument); siting methods and strategies used for Class B TREMOR instruments and those that can be used for Class C instruments to preserve the cost advantages of such systems; and some general discussion of MEMS accelerometers, including a comparative Table with representative examples of Class A, B and C MEMS devices. (“MEMS” means “Micro-ElectroMechanical” Systems—“micromachined” sensors, generally of silicon. Classes A, B, and C are defined in Table 1.)

Open-File Report↗
USGS1994

Including near-field terms in the isochrone integration method for application to finite-fault or kirchhoff boundary integral problems

In many types of seismological and engineering problems, it is necessary to perform a surface integral involving a Green's function having either a source or receiver point on the surface. For far-field terms of the Green's function, it is well known that the surface integral can be reduced to a line integral, yielding a considerable computational advantage. In this work we show that a similar transformation to a line integral can be made for the near-field terms when the Green's function is for a uniform whole space. The necessary condition is that the various terms in the Green's function can be transformed into sums of nondispersive pulses. We accomplish this for near-field terms in a whole space by repeatedly time-differentiating the terms.

Bulletin of the Seismological Society of America↗