DIRECTION DETERMINATION The three degrees of freedom, latitude, longitude, and elevation (or equivalents), constitute a rectangular coordinate system (neglecting earth curvature effects), and clearly determination of the orientations of the axes is important. The vertical direction is usually defined by means of a level or plumb line. Horizontal orientation can be determined with respect to the position of a celestial body, the Earth's rotation, magnetic north, or a previously known orientation. Although the most obvious celestial orientation is by sighting on Polaris (which is not exactly at the celestial pole), any star can be used. Sighting on the Sun ( sun shots ) permits orientation during daylight. Nightime observations can establish orientation to a fraction of an arc second (arcsec). Gyrocompass orientation is extensively used in marine and airborne surveys. A gyrocompass gives orientation with respect to true north within about 20 arcsec. A magnetic compass is often used to determine direction with respect to magnetic north, correction for the magnetic declination giving true north. Diurnal variations may create 10 min of error, more during magnetic storms. Care has to be exercised that no local iron or electric currents distort the magnetic field. Benchmarks (identified points of known location) often have nearby reference points (azimuth bars) that can be used to establish orientation. DISTANCE MEASUREMENT Direct measurement of distance is done by seeing how many times a standard measure will fit between points whose separation is to be determined, a technique called chaining , the unit of measure usually being a steel tape (a chain ) of precise length.

Applied Geophysics: Appendix B. Location Determination

Quantification of human impact on water, sediment, and nutrient fluxes at the global scale demands characterization of reservoirs with an accuracy that is presently unavailable. This letter presents a new method, based on virtual dam placement, to make accurate estimations of area-volume relationships of large reservoirs, using solely readily available elevation data. The new method is based on regional similarity of area-volume relationships. The essence of the method is that virtual reservoirs are created in the vicinity of an existing reservoir to derive area-volume relationships for the existing reservoir. The derived area-volume relationships reproduced in situ bathymetric data well. An intercomparison for twelve reservoirs resulted in an average R2 = 0.93. This is a significant improvement on estimates using the best existing global regression model, which gives R2 = 0.54 for the same set of reservoirs.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016GL069816

Determining water reservoir characteristics with global elevation data

Bathymetric survey of Lake Naivasha and its satellite Lake Oloiden in Kenya; using acoustic profiling system

The Cerro Prieto dam, a relatively small water reservoir in NE Mexico, is one of the main resources of potable water for Monterrey, a city with a population of about four million inhabitants. A high resolution seismic study using non-linear parametric sub-bottom echo-sounder SES-2000 was carried out in this water reservoir. High resolution acoustic data interpretation shows that the thickness of recent sediments due to siltation of the reservoir reaches 3.5-4.0 m. It shows a high recent sedimentation rate (1-2 up to 14 cm/ year). Based on the echo-sounder data, the first bathymetric map and a digital model of recent sediment thickness were designed. A significant (5-12%) difference between the volume capacity value used by National Commission of Water (CNA) and acoustic survey results was revealed. Differences between the CNA and acoustic data indicate storage losses from 12-17 up to 30 million cubic meters. The results obtained through study such as this one, could be useful to improve a water resources management.

http://www.scielo.org.mx/pdf/geoint/v53n1/v53n1a3.pdf

Bottom topography, recent sedimentation and water volume of the Cerro Prieto Dam, NE Mexico

Sediment distribution and accumulation in Lake Naivasha, Kenya over the past 50 years

Paleogeographic development of the surroundings of Cerro Prieto water reservoir, Pablillo basin, NE Mexico, and geophysical modeling of the reservoir subsurface

Gravity data are sensitive to local vertical offsets across high-angle faults, where rocks with different densities are juxtaposed. Yet high densities in some Mesozoic sedimentary rocks just above the basement may smear out the subtle gravity signatures of basement faults. At this study the gravity data processing tends to avoid ill-described “black-box” techniques. The study area is situated in the Palomas site, Cuatrocienegas region, Coahuila, NE Mexico. The San Marcos Fault is at least 300 km long and has WNW-ESE trend from the central part of Nuevo Leon State through Coahuila, and finally to the eastern part of Chihuahua State. Gravimetric data shows that the lowest values of free air and Bouguer anomalies are in the southern part of the area, and the highest values are in the western and central part of the area. Between these parts exists a zone of high horizontal gravity gradient. Configuration of linear elements of gravity field (gradient zones) delimited the San Marcos Fault in the San Marcos valley below thickness of recent sedimentary cover. Two density models were carried out, which showed that the Cretaceous rocks are in discordant contact with the Paleo- zoic rocks that can be related to the San Marcos Fault. The density was determinate using to Nettleton’s method, which results highlight the presence of the San Marcos Fault. Density models showed that the Quaternary sediments are in direct contact with the San Marcos Fault.

https://file.scirp.org/pdf/JMP20122900017_17462684.pdf

Gravity Field Variations Associated with the Buried Geological Structures: San Marcos Fault (NE Mexico) Case Study

In this work, the integral analysis of gravity and aeromagnetic data in the La Popa Basin and the adjacent geologic structures is presented. The analysis was complemented with a Digital Model of Elevations that, combined with the review of previous geological studies, served to compare the surface structures and basement blocks in the study area. The most important tectonic blocks were distinguished and finally two 2.5D geological-geophysical models were developed. These models represent in a general way the most important structural characteristics of the northeast of Mexico.

/pdf/rasgos-tectonicos-de-la-cuenca-de-la-popa-y-de-las-1j52xuk68c.pdf

Rasgos tectónicos de la Cuenca de La Popa y de las estructuras que la rodean en el noreste de México derivados de campos geofísicos potenciales

Northeast Mexico is in essence the juncture of two distinctly different tectono-stratigraphic provinces, the eastern Gulf of Mexico (Coastal Plane, Sierra Madre Oriental) province and the western Pacific Mexico (Rivera plate, Meso-American trench, Sierra Madre Occidental) province (Goldhammer & Johnson, 2001). Tectonic evolution of northeast Mexico was dominated by divergent-margin regime associated with the opening of the Gulf of Mexico and overprinted by non-igneous Laramide orogenic effects (Pindell et al., 1988). The structural grain of northeast Mexico consists of Triassic to Liassic fault-controlled basement blocks, the development of which reflects in part late Paleozoic orogenic patterns of metamorphism and igneous intrusion (Wilson, 1990). Several tectonic provinces may be recognized by interpretation of the basement and sediment cover: Coahuila Block, La Popa Basin, Sabinas Basin, Burgos Basin, Sierra Madre Oriental (Monterrey Trough), and Parras Basin (Yutsis et al., 2009, Fig. 1). Mojave-Sonora Megashear and San Marcos Fault (Chavez-Cabello et al., 2007) are two principal fault zones crossing the northeast Mexico in NW-SE direction. La Popa Basin is located on the foreland of the Sierra Madre Oriental, 85 km northwest of the city of Monterrey, N.L., northeast of Parras Basin and south of the Sabinas Basin (Fig. 2). The basin’s development is greatly defined by salt tectonics, and is of great interest to the petroleum industry (Hudec and Jackson, 2007; Jenchen, 2007), due to the fact that many of oil reservoirs in the world are located in salt basins (e.g. Gulf of Mexico, the Persian Gulf, the North Sea, Lower Congo Basin, Campos Basin, etc.) (Warren et al., 1999). La Popa Basin is the best analogue of the Gulf of Mexico (Willis, 2001). Although no oil or gas deposits were found in it so far, understanding of its structure and geological evolution can be applied to similar areas whether they are located in the continent or offshore. The Bouguer gravity and the total field aeromagnetic data were supplied by Geological Survey of Mexico (SGM), Pemex Exploration and Prospecting, published data (Mickus et al., 1999), and authors field works (Yutsis et al., 2009, Tamez et al., 2010, in press).

/pdf/geophysical-modeling-of-the-surroundings-of-la-popa-basin-ne-3xo2klcfh5.pdf

Konstantin Krivosheya

Papers

Bottom topography, recent sedimentation and water volume of the Cerro Prieto Dam, NE Mexico

Paleogeographic development of the surroundings of Cerro Prieto water reservoir, Pablillo basin, NE Mexico, and geophysical modeling of the reservoir subsurface

Gravity Field Variations Associated with the Buried Geological Structures: San Marcos Fault (NE Mexico) Case Study

Rasgos tectónicos de la Cuenca de La Popa y de las estructuras que la rodean en el noreste de México derivados de campos geofísicos potenciales

Geophysical Modeling of the Surroundings of La Popa Basin, NE Mexico, with Gravity and Magnetic Data