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T.G. Hildenbrand

Publications and source records attributed to T.G. Hildenbrand.

At least 37 records · Page 2Linked to original sources
USGS1996

Quantitative investigations of the Missouri gravity low: A possible expression of a large, Late Precambrian batholith intersecting the New Madrid seismic zone

Analysis of gravity and magnetic anomaly data helps characterize the geometry and physical properties of the source of the Missouri gravity low, an important cratonic feature of substantial width (about 125 km) and length (> 600 km). Filtered anomaly maps show that this prominent feature extends NW from the Reelfoot rift to the Midcontinent Rift System. Geologic reasoning and the simultaneous inversion of the gravity and magnetic data lead to an interpretation that the gravity anomaly reflects an upper crustal, 11-km-thick batholith with either near vertical or outward dipping boundaries. Considering the modeled characteristics of the batholith, structural fabric of Missouri, and relations of the batholith with plutons and regions of alteration, a tectonic model for the formation of the batholith is proposed. The model includes a mantle plume that heated the crust during Late Precambrian and melted portions of lower and middle crust, from which the low-density granitic rocks forming the batholith were partly derived. The batholith, called the Missouri batholith, may be currently related to the release of seismic energy in the New Madrid seismic zone (earthquake concentrations occur at the intersection of the Missouri batholith and the New Madrid seismic zone). Three qualitative mechanical models are suggested to explain this relationship with seismicity. Copyright 1996 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS1996

Rationale and preliminary operational plan for a high-altitude magnetic survey over the United States

A proposed high-altitude survey of the U.S. with an ER-2 to collect radar data offers an exciting and cost-effective opportunity to collect magnetic anomaly data. At this workshop, a group of magnetic specialists addressed this opportunity by discussing the need for high-altitude magnetic data and by formulating a preliminary operational plan to acquire such data. The high-altitude aeromagnetic survey would provide critical data needed to expand our knowledge of the geomagnetic field, with applications to a variety of earth science issues including geology, tectonics, core-processes, and rock-magnetism. Test flights with a cesium magnetometer indicate that the ER-2 has the potential to measure the magnetic field at an accuracy of 2 nT or better along flight lines. If the national ER-2 survey is carried out, the successful collection of high-altitude magnetic data hinges on establishing a consortium of federal and state agencies, private industry, and academic institutions to provide the identified resources.

Open-File Report↗
USGS1995

Geophysical setting of the Reelfoot Rift and relations between rift structures and the New Madrid seismic zone

In the winter of 1811-12, three of the largest historic earthquakes in the United States occurred near New Madrid, Missouri. Seismicity continues to the present day throughout a tightly clustered pattern of epicenters centered on the bootheel of Missouri, including parts of northeastern Arkansas, northwestern Tennessee, western Kentucky, and southern Illinois. In 1990, the New Madrid seismic zone/Central United States became the first seismically active region east of the Rocky Mountains to be designated a priority research area within the National Earthquake Hazards Reduction Program (NEHRP). This Professional Paper is a collection of papers, some published separately, presenting results of the newly intensified research program in this area. Major components of this research program include tectonic framework studies, seismicity and deformation monitoring and modeling, improved seismic hazard and risk assessments, and cooperative hazard mitigation studies.

Professional Paper↗
USGS1983

FFTFIL; a filtering program based on two-dimensional Fourier analysis of geophysical data

The filtering program 'fftfil' performs a variety of operations commonly required in geophysical studies of gravity, magnetic, and terrain data. Filtering operations are carried out in the wave number domain where the Fourier coefficients of the input data are multiplied by the response of the selected filter. Input grids can be large (2=number of rows or columns=1024) and are not required to have numbers of rows and columns equal to powers of two.

Open-File Report↗