IAMG 2001--Cancún Technical Program--Session D

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Preliminary geostatistical analisys of Geomagnetic Spatial correlation between the Radon-222 and Radio-226 concentrations collected from Los Azufres Geothermal reservoir in fractured rocks by Jesus Hernan Flores-Ruiz*, Instituto Mexicano del Petroleo, Mexico, Juan Esteban Hernandez-Quintero, Universidad Nacional Autonoma de Mexico, Mexico, J. Urrutia Fucugauchi, Instituto de Geofisica UNAM, Mexico and R. Martinez Angeles, Instituto Mexicano del Petroleo, Mexico The area in study is of 40 km2 and it is located in the northeast part of the Mexican State of Michoacán and to the southeast of the geothermal field Los Azufres inside the geologic province of the Mexican Volcanic Belt (MVB). In the place exist a series of faults of orientation east-west and northeast-southwest. These faults give origin to grabens and horst produced by regional distensives efforts with north-south preferential orientation. In these geologic structures it was carried out the exploration of gas Radon-222 (Rn-222) it was superficial and samples of volcanic rocks and soil, it being a bigger content of Radio-226 (Ra-226) in the floor samples. It was considered the maximum correlation distance between the data of Rn-222 and Ra-226 in the orthogonal directions (E-W, N-S, NE-SW and NW-SW). It is not necessary to forget that Radon gas has been used to measure dynamic processes, the resultant anomalies are considered the definition of the extension approximately in the underground of the thermal area for local structures that are continuous in the surface. This consideration is obvious, however, this is valid if the geologic structures are deep or near to the vertical one. It was also determined the space combined relationship between the emanations of the Rn-222 and the content of Ra-224 in the field samples for the method of Cokriging, it was estimated relationship between these two variables is respectively from 1 to 26. On the other hand it is significant the relationship between the permeable area and the density of radon measurements in the place. This factor would seem to be the most important in this area where there is a fault that can be activated due to the flow of heat through its comparing with a broadly permeable area. But the success of the radon emanations has been had by means of the biggest quantity from traverse profiles to the fault trace appearances in the geothermal field. Paper in PDF format Flores-Ruiz and others, Acrobat PDF, 240 k.