ABSTRACT Microseismic logging technology was applied to a Devonian Shale well in the Appalachian Basin to evaluate the height and orientation of a hydraulic fracture. The technique was used in the Sterling Drilling and Production Company Jarvis No. 1143, which is the Gas Research Institute's (GRI) Comprehensive Study Well No. 2 (CSW 2). The well, completed in the Devonian Shales, is located in Calhoun County, WV. This was the first application of the fracture mapping procedure in the Appalachian Basin; it was performed as part of GRI's efforts to understand fracture growth and orientation in the Devonian Shales. The procedure was also unique in that it was the first time the seismic data were collected in a gas-filled wellbore and after a well had been produced for an extended period of two years. The microseismic logging analysis results on CSW 2 indicate a 200-ft fracture height with an orientation trending Ν34°E. Also presented in this paper are the results obtained from a series of hydraulic fracture diagnostic tests performed on the CSW 2 prior to the microseismic logging experiment

Six strain and inertial seismographs at Queen Creek, Arizona (QC-AZ), recorded six modes of surface waves from a suite of 18 earthquakes near Chiapas, Mexico. The six group-velocity dispersion curves were used in a least-squares inversion to estimate the shear velocity structure of the upper 380 km of crust and mantle in central Mexico. Multiple filter analysis of 108 seismograms produced group velocity dispersion curves slower than average continental paths. The range of the average deviation from the mean dispersion curve for the fundamental modes was 0·025 to 0·160 km s−1 for Rayleigh waves and 0·025–0·281 km s−1 for Love waves. The inversion models have low velocities that correspond with a representative geotherm andpetrologic P-T diagrams to indicate partial melting. The 4-layer crust is 30 km thick with a high-temperature gradient LVZ in the granitic layer and with a LVZ in the lower 8 km of a basaltic layer resulting from a high geothermal gradient or from partial melting of water saturated rock. The mantle has a 4–8 km thick solid lid and a shallow low velocity zone. The lowest velocities correspond to 10–20 per cent partial melting. A sharp velocity gradient at 70–80 km probably results from both the phase change to garnet pyrolite and the lower extreme of partial water pressure with the disappearance of amphiboles from the host pyrolite. Based on the velocities, 5 per cent anhydrous melting extends to 260 km. From 300 to 380 km temperature gradients and crystal lattice instabilities prior to the olivine-spinel phase change produce another LVZ. A hypothesis is presented that the large volume of low density magma produces a regional vertical force that creates high flat plateaus as found in central Mexico and the Colorado Plateau. The inversion models have a 7·5 s S-wave residual relative to the Canadian Shield model CANSD in agreement with observed US station anomalies.

Abstract Theoretical expressions for the spectra of the noise in a galvanometer, a seismometer, and a seismometer-galvanometer seismograph are derived from electrical analog circuits and from the Johnson noise of the resistive elements in these circuits. The contributions of the internal damping of the seismometer and of the galvanometer, and of the series resistor to the total potential energy of the thermal noise in a high-sensitivity long-period seismograph are explicit in the expressions. The theoretical thermal spectra agree with observations made at Las Cruces, New Mexico (LC-NM), and at Queen Creek, Arizona (QC-AZ). At LC-NM, the outputs from two matched vertical seismographs were subtracted to obtain estimates of the individual seismograph noise at periods from 4 to 800 sec. Additional experiments demonstrated that the seismograph noise between 10 and 1,000 sec could be estimated equally well by replacing the seismometer: (1) with a resistor, (2) with a coil and magnet oriented vertically or north-south, or by (3) rigidly blocking the seismometer mass. The observed spectra from LC-NM indicate an excess noise in the electronics of the galvanometer phototube amplifier (GPTA) having a one-over-f character at periods longer than 300 sec. At QC-AZ, seismograph noise was recorded with a resistor substituted for the seismometer. The observed noise spectra agree identically with the theoretical noise spectra at periods from 25 to 60 sec and with theoretical noise spectra plus a 1/f noise in the GPTA electronics at periods out to 2,560 sec. The QC-AZ observed and theoretical noise spectra are plotted from 3 to 2,560 sec as the mean-square voltage at the seismograph output and as the root-mean-square displacement of the ground that would produce the same signal as the noise. Typical minimum vertical amplitude spectra of the microseismic background are above the instrument noise spectra in the period range from 3 to 2,560 sec. The agreement between the theoretical thermal noise spectra and the two sets of observational spectra confirms the validity both of the theoretical expressions and of the experimental procedures.

abstract Amplitude spectral density of the ambient earth motion in the vertical and horizontal directions at a quiet site are given in graphical and tabular form over the five decades of period from 0.1 to 2560 sec. Comparison of these spectra in the period range between 0.1 and 3 sec with the Brune and Oliver (1959) minimum curve and in the period range between 10 and 100 sec with spectra from the mines at Las Cruces, New Mexico, and Ogdensburg, New Jersey, indicate that in these period ranges the spectra are representative of the quietest seismograph stations presently known. These spectra can serve as a guide for seismologists and other scientists interested in the quiescent vibrations of the ground.

Abstract A seismograph complex consisting of short-period (SP), long-period (LP), and extended long-period (XLP) inertial and strain seismographs has been installed. Recordings are made on magnetic tape and photographic film. Routine magnifications on the 20-trace, 16-mm film recorders for all three components are: SP inertial, 500 K; LP inertial, 100 K. The noise levels permit equivalent magnifications on the strain seismographs. The complex provides seismic wave discrimination by directional response, which is independent of period, and by detection of differences in phase velocities between P, S, Love, or Rayleigh arrivals. The strain seismographs use 40-m-long rods and moving coil transducers with generator constants of 32,000 v/m/sec. They sense waves of 5 × 10-13 strain at 30 sec and reject the 2 × 10-8 earth-tide strain. A low-noise preamplifier drives a filter assembly which provides SP, LP, and XLP strain outputs. The complex is installed in an abandoned mine 50 km southeast of Phoenix, Arizona. Environmental control is provided by burial at a depth of about 110 m in a quartz diorite, by sealing the mine, and by insulating the seismometers.