Geology topics

Huaibao P. Liu

Publications and source records attributed to Huaibao P. Liu.

3 recordsLinked to original sources

USGS2006

Improved phase-ellipse method for in-situ geophone calibration

For amplitude and phase response calibration of moving-coil electromagnetic geophones two parameters are needed, namely, the geophone natural frequency, f 0 , and the geophone upper resonance frequency f u . The phase-ellipse method is commonly used for the in situ determination of these parameters. For a given signal-to-noise ratio, the precision of the measurement of f 0 and f u depends on the phase sensitivity, f(δφ/δf) For some commercial geophones f(δφ/δf) at f u can be an order of magnitude less than the sensitivity at f 0 . In this paper we present an improved phase-ellipse method with increased precision. Compared to measurements made with the existing phase-ellipse methods, our method shows a 6- and 3-fold improvement in the precision, respectively, on measurements of f 0 and f u on a commercial geophone.

Geophysical Prospecting↗

USGS2006

A new Lagerstätte from the Middle Ordovician St. Peter formation in northeast Iowa, USA

A new fossil fauna has been discovered from a recently recognized shale unit within the middle Ordovician St. Peter Formation in northeast Iowa. It contains a variety of invertebrates and vertebrates, including soft body tissues, impressions, and 3-dimensionalpreservations. The exceptional preservation reveals a new Konservat-Lagerstätte, the Winneshiek Lagerstätte, and opens a unique window into the community that inhabited the margins of the Laurentian cratonic seaway during Middle Ordovician transgression. Among the fossils, several conodont assemblages, including the apparatus of enigmatic coleodontids, are preserved. Some conodont assemblages associated with soft body tissues are particularly noteworthy.

Geology↗

USGS1998

Effect of cable capacitance on in-situ borehole geophone calibration

Using 2-Hz electromagnetic moving‐coil geophones as sensing elements, we have constructed and deployed three‐component seismometers in boreholes at various sites for wave‐propagation studies associated with earthquake hazards (Liu et al., 1991). For example, one such seismometer has been deployed in a 88-m deep borehole reaching bedrock in the Marina District of San Francisco since 1990 (Liu et al., 1992) for the purpose of comparing ground motions in the bedrock and those at the surface. Periodic calibrations for such geophones are necessary to check if the geophone parameters have changed because of decreased magnetization of the geophone ferro‐magnet. For example, the coil transductance of the vertical‐component geophone of the borehole seismometer mentioned above was calibrated to be 121 V-s/m using phase‐ellipse test and step test before deployment. Sixty six months after the deployment, the coil transductance, when calibrated in situ and with a 100-m intervening cable between the geophone and the calibration instrument, was found to be 114 V-s/m.

Geophysics↗