Bol. Soc. Geol. Mexicana. Tomo XLVIII, No. 1, 1987

Resultados de los estudios sismológicos de gran visión realizados en las fallas Vallecitos-Calabazas, en el norte de Baja California

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http://dx.doi.org/10.18268/BSGM1987v48n1a3

Cecilio J. Rebollar* y Antonio Uribe Carbajal**

*Centro de Investigaciones Científicas y de Educación superior de Ensenada, B. C.
**Comisión Federal de Electricidad.

Abstract

We analyzed the seismicity (1. 4 ≤MI1≤3.4) recorded by a network of five portable stations deployed along the Vallecitos-Calabazas fault systern (VCFS) during 1983, as well as the activity from VCFS recorded at the permanent seismic station CBX from 1982 to 1986.

We found an average of 7.3 events per month distributed over the distance range from 8 to 53 km (1.0≤S-P≤7.0 seconds). There is an apparent nonstationarity of seismicity as indicated by a plot of cumulative number of events versus time. The b-value is found to be 1.41 which is high compared to that of 0.92 for the adjacent similar (strike-slip) San Miguel Fault. This difference in b-values suggests a higher stress environment along the San Miguel Fault than in the VCFS. In other words, the stresses in VCFS are widespread in a large volume and not concentrated in a particular shear plane. We calculated the rate of seismic slip for two years time period of local events recorded at station CBX (308 events), and  from a time sample of earthquake spanning from 1934 to 1980. We found a rate of seismic slip of 0.030 mm/year for the first sample and 0.028 mm/year for the second sample or approximately one millimeter every 30 years

These two estimates are very similar and suggest that the strain energy accumulated in this area is released in a series of small earthquakes.

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