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 ML ≥ 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 9.20×1018 dyn cm to 2.33×1024 dyn cm. Earthquakes with seismic moment greater than about 1.0×1021 dyn cm had nearly constant stress drops (≃ 50 bars); earthquakes with seismic moment less than about 1.0×1021 dyn cm had stress drops that apparently decrease as seismic moment decreases.

We compare the attenuation of high‐frequency (3–30 Hz) shear waves for crustal paths in New York State, South Africa, and southern California over source‐receiver distances of about 10–400 km. The data consist of digital recordings of S waves (Δ = 5–100 km) and Lg waves (Δ = 100–400 km) produced by earthquakes. We use a coda normalization method to remove the effects of site amplification and source excitation from the amplitudes of the S and Lg waves. Over the entire distance range studied (10–400 km), the amplitude decay of 3‐Hz shear wave energy is considerably less for the tectonicaily stable areas of New York and South Africa than for the tectonicaily active region of southern California. High‐frequency (30 Hz) S wave attenuation is significantly less for New York and South Africa than for southern California, for distances between 15 and 90 km. We parameterize the decay with distance (R) of coda‐normalized shear wave amplitudes with a frequency‐independent Q and geometrical spreading exponent γ, where geometrical spreading is proportional to R−γ. For New York State the S wave amplitude decay (3–30 Hz) is well described by a frequency‐independent Q of 2100−330+490 and γ of 1.3±0.1. The decay of Lg wave amplitudes from 3 to 15 Hz in the New York State region is fit with a frequency‐independent Q of 1600−280+330 γ of 0.70±0.2. The S wave amplitudes (3–30Hz) in South Africa yield a Q of 1500−190+380 and γ of 1.3±0.1. Fixing the geometrical spreading at R−0.5 produces an Lg wave Q estimate at 3 Hz in South Africa of 360−50+80. This Lg wave Q is low considering that South Africa is a cratonic, tectonicaily stable area. The S wave amplitudes from southern California are described with a frequency‐independent Q of 800−150+240 and a large geometrical spreading exponent of γ of 1.9±0.2. We find an Lg wave Q at 3 Hz of 260±30 for southern California, after constraining the geometrical spreading at R−0.5.

An effective solution to the problem of the detection and identification of low-yield coupled and fully decoupled underground nuclear explosions appears available via use of high-frequency seismicf data ranging up to 30 or 40 Hz. In order to evaluate detection-identification capabilities when using such data, it is necessary to estimate (1) spectral characteristics and relative amplitudes of both P and S waves from explosions and earthquakes over the frequency band from 5 to 40 Hz, (2) signal transmission characteristics over this band through pertinent types of earth structure, and (3) recording system and ground noise characteristics over this frequency band. In this study, each of these topics is considered in turn as they relate to detection and discrimination of the signals from low-yield coupled and decoupled explosions in the regional and teleseismic distance ranges. Estimates of the capabilities of specific hypothetical networks to detect and identify (insofar as signal-to-noise ratio is an important factor in identification) explosions within the USSR are then considered. These estimates of signal detection capability provide the central focus for the study as they serve to translate diverse and rather complex sets of observational data and theory into concrete predictions of monitoring capability. Following the assessment of detection capabilities, the problem of identification of small events is considered, with particular emphasis on discrimination at regional distances where the network is calculated to provide signals of high signal-to-noise ratio. The principal results and conclusions of this study are as follows: (1) seismic system noise can be suppressed to levels well below ground noise at quiet sites up to frequencies at least as high as 30-40 Hz when using presently available hardware; (2) average amplitudes of high-frequency noise in a variety of geological environments are very low and change little with time or season; (3) transmission of high-frequency P and S wave signals in the regional distance range in stable continental areas and shields is nearly as efficient as at 1 Hz, with effective Q factors in shield areas being about 9000 and 4000 for high-frequency Pn and Sn, respectively, while the effective Q for P, waves in tectonic areas is about 1000; (4) a properly designed and deployed network of 25 simple three-component nonarray stations internal to the USSR and 15 similar stations surrounding the USSR is predicted to be capable of multistation detection at high signal-to-noise ratio of fully decoupled 1-kt explosions located at all potential decoupling sites within the USSR; (5) by inference from the quantitative agreement of empirical observations and theoretical predictions, when using lower-frequency data over a great range of explosion yields, we conclude that procedures based on the use of both detectable P and S waves will serve to identify explosion-generated seismic signals at least as small as those expected from a fully decoupled 1-kt explosion.

The Whittier Narrows earthquake sequence (local magnitude, M(L) = 5.9), which caused over $358-million damage, indicates that assessments of earthquake hazards in the Los Angeles metropolitan area may be underestimated. The sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east-west length of the northern margin of the Los Angeles basin. Peak horizontal accelerations from the main shock, which were measured at ground level and in structures, were as high as 0.6g (where g is the acceleration of gravity at sea level) within 50 kilometers of the epicenter. The distribution of the modified Mercalli intensity VII reflects a broad north-south elongated zone of damage that is approximately centered on the main shock epicenter.