Development of LP Wave Discrimination Capability Using LP Strain Instruments

Fix, James E.; Sherwin, John

doi:10.21236/ad0869214

Cited by 4 publications

(4 citation statements)

References 49 publications

(76 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Very few heat flow determinations have been made in this province (Roy, Blackwell & Decker 1972). However, the Sn velocity across the Colorado Plateau from Rangely, Colorado, to QC-AZ is about 10 per cent slower than the Sn velocity from the Nevada Test Site (NTS) to QC-AZ (Fix & Sherwin 1972). This significantly slower shear-wave velocity suggests that the Colorado Plateau may have a mantle similar to central Mexico.…”

Section: J E Fixmentioning

confidence: 95%

The Crust and Upper Mantle of Central Mexico

Fix¹

1975

Geophysical Journal International

View full text Add to dashboard Cite

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 380km 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 kni s-' for Rayleigh waves and 0.025-0.281 km s-l for Love waves. The inversion models have low velocities that correspond with a representative geotherm and petrologic P-Tdiagrams to indicate partial melting. The 4layer 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 Aat plateaus as found in central Mexico and the Colorado Plateau. The inversion models have a 7.5s S-wave residual relative to the Canadian Shield model CANSD in agreement with observed US station anomalies.

show abstract

Section: J E Fixmentioning

confidence: 95%

The Crust and Upper Mantle of Central Mexico

Fix¹

1975

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…amplitudes of the spectrum in the final band of interest, and at frequencies that alias into this. Between earthquakes, the spectrum of earth strain up to 10 sec (Fix and Sherwin, 1972;Berger and Levine, 1974;Beavan and Goulty, 1977) diminishes smoothly with frequency. There will thus be little aliasing from frequencies just above the final Nyquist frequency.…”

Section: Design Resultsmentioning

confidence: 99%

Designing Compact Causal Digital Filters for Low-Frequency Strainmeter Data

Agnew¹,

Hodgkinson²

2007

Bulletin of the Seismological Society of America

View full text Add to dashboard Cite

For the strainmeter component of the Plate Boundary Observatory, filters are needed to produce low-frequency series (5-minute samples) from the higherfrequency (1 Hz) data generated by the instruments. We present design methods for finding filters that are efficient, causal, and compact. We use standard methods for generating symmetric finite impulse response filters, followed by root finding, selection of roots, and reconstruction of the weights, using procedures that make these processes numerically stable. The final filters show appropriate performance even in the presence of large teleseismic signals, but introduce unavoidable artifacts for strain data from large local earthquakes.

show abstract

“…Surface disturbances from atmospheric turbulence and other nearby sources cause an ordinary horizontal component seismograph to tilt, thereby giving it a component of gravitational acceleration, which reads out as if it were horizontal motion. In an extensive investigation of earth noise, Fix and Sherwin [1972], using strain and inertial seismographs in combination, showed that the spectrum of true horizontal noise closely matched the spectrum of vertical noise in amplitude, minor peaks falling sometimes above, sometimes below, the corresponding peaks of the vertical noise. Further, Sorrells et al [1971] showed that apparent (tilt effect) horizontal components of local earth noise decrease considerably with depth of installation of the seismometer.…”

Section: Uniform Representation Of Earth Noise Datamentioning

confidence: 89%

“…In a later report, Fix [1973] shows a plot of instrument noise with a dummy resistor in place of the seismometer, and it is clear that his observed amplitude of'earth' noise is at least 2 or 3 times the observed instrument noise. To show that the instrument noise is a minor contribution, I have plotted as a branch curve an estimated 'true' earth noise, and it can be seen that the logarithm of the difference usually does not exceed 0.125, or 1.25 dB.…”

Section: Uniform Representation Of Earth Noise Datamentioning

confidence: 96%

The sensitivity and dynamic range of inertial seismographs

Melton¹

1979

Physics of the Earth and Planetary Interiors

View full text Add to dashboard Cite

Development of LP Wave Discrimination Capability Using LP Strain Instruments

Cited by 4 publications

References 49 publications

The Crust and Upper Mantle of Central Mexico

The Crust and Upper Mantle of Central Mexico

Designing Compact Causal Digital Filters for Low-Frequency Strainmeter Data

The sensitivity and dynamic range of inertial seismographs

Contact Info

Product

Resources

About