| Title | Resistivity and Self-Potential Study in the Southern Part of the Mexicali Valley |
|---|---|
| Authors | S. Diaz C., J. F. Arellano |
| Year | 1979 |
| Conference | DOE-CFE Symposium on Cerro Prieto |
| Keywords | |
| Abstract | In order to obtain information about the geothermal possibilities in the Southern part of the Mexicali Valley, the Comision Federal de Electricidad has performed complementary geological, geochemical and geophysical studies in an area covering approximately 600 km2 located between Mesa de Andrade and Estacion Guadalupe Victoria, B. C. (Fig. 1). The geothermal activity in this area is characterized by the presence of abnormal water temperatures, ranging from 35° to 45°C, in some of the shallow wells drilled to a depth of 100 m by the Secretarea de Agricultura y Recursos Hidraulicos (SARH). The structure of this zone is affected by the Cerro Prieto fault, which can be seen in the surface of the northeastern part of Mesa de Andrade, and in its southeast continuation down to the Gulf of California. The Cerro Prieto geothermal field is located in the northeastern extreme of the fault, thus the thermal activity in the field has been related to the fault. Based on the geology of the area and on results from the geoelectric study performed in the northern part of the Mexicali Valley, two regional geophysical surveys were programmed by means of electric resistivity and self-potential methods. One hundred and ten vertical electric soundings were performed for the geoelectric survey, using a Schlumberger arrange with a 10 km maximum spacing between current electrodes (AB/2 5000 m), in six regional lines approximately 20 km long and with a northeast-southwest strike (lines No. 18, 19, 20, 21, 22, and 23) crossing perpendicularty the Cerro Prieto fault. To complement the resistivity study a selfpotential survey was performed measuring differences in the potential between two non-polarizing electrodes 200 m apart. The "leap frog" technique was followed on the six regional lines and on another three closing loop lines with a length of about 35 km each and a northwestsoutheast strike (lines A, B, and C). Con el fin de obtener informaci6n sobre las posibilidades geotermicas de la parte sur del Valle de Mexicali, la Comisi6n Federal de Electricidad ha realizado estudios complementarios geol6gicos, geoqu{micos y geof(sicos en un area de aproximadamente 600 km2, en la regi6n oomprendida entre Mesa de Andrade y la Estaci6n Guadalupe Victoria, B. C. (Fig. 1). En esta zona, la actividad geotermica se caracteriza por la presencia de temperaturas anormales -de 35° a 45°C-en el agua de algunos pozos someros perforados a la profundidad de 100 m por la Secretar(a de Agricultura y Recursos Hidraulicos (SARH). Estructuralmente, la zona esta afectada por la faIia de Cerro Prieto, ·visible superficialmente en la parte NE de la Mesa de Andrade y en su prolongaci6n al SE hasta el Golfo de California. En el extremo NO de la falIa se encuentra el campo geotermico de Cerro Prieto, cuya actividad termal se ha relacionado con ella. Con base en la geolog(a del area y el resultado del estudio geoelectrico efectuado en la parte N del Valle de Mexicali, se programaron dos levantamientos geof(sicos regionales mediante los metodos de resistividad electrica y potencial espontaneo. Para el levantamiento geoelectrico se ejecutaron 110 sondeos electricos verticales, utilizando el dispositivo Schlumberger con espaciamiento maximo entre electrodos de corriente de 10 km (AB/2 = 5000 m), en seis Ifneas regionales de 20 km de longitud aproxima" damente, con rumbo NE-SO (I(neas Nos. 18, 19, 20, 21, 22 y 23) para cruzar perpendicularmente la falla Cerro Prieto. Como complemento del estudio de resistividad se lIev6 a cabo un levantamiento de potencial espontaneo, con mediciones de diferencias de potencial entre dos electrodos no polarizables separados 200 m, siguiendo la tecnica de saito de rana, sobre las seis I (neas regionales anteriores y en otras tres Hneas de cierre de pol(gonos con una longitud de 35 km cada uno aproximadamente y rumbo NO-SE U(neas A, By C). |