Anomalies in Geomagnetic Variations across the Central Gulf of California

Abstract

Geomagnetic field variations have been observed at four stations in the central Gulf of California and at one Pacific coast station at the same latitude. The four Gulf stations comprise two pairs of stations on opposite sides of the Gulf; one pair, at El Barril and Bahia Kino, was placed across what was thought to be a long section of transform fault in the Gulf and the second pair, at Mulege and Guaymas, was placed across the Guaymas basin which is a proposed site of an ocean ridge type spreading centre. Variations in the vertical component of the magnetic field show almost complete reversal on opposite sides of the Gulf in the frequency range 0.25–4.0 c hr-1. Analysis of the data indicates that induced electric currents flow in and under the Gulf of California. Models for 1 chr-1 suggest that the surface conductor alone is insufficient to account for the surprisingly large anomaly between El Barril and Bahia Kino. Although only a small number of data points is available it is thought that this anomaly indicates the possible existence of a spreading centre between these two stations. The suggestion is therefore made that the fracture pattern for the central Gulf of California includes a spreading centre at the San Pedro Martir basin. A consequence of this is that the fracture pattern must change with time. No explanation of this changing fracture pattern is attempted but its occurrence would account for the presence of the many islands in the Gulf of California.