The intermediate earthquake source near Bucaramanga, Colombia

abstract An intensive source of intermediate depth earthquakes has been located in northern Colombia. The activity of this source increased significantly between 1956 and 1966, but appears to be decreasing after 1966. The frequency-magnitude relation of the Bucaramanga earthquakes is anomalous, with fewer large earthquakes than expected. The distribution of determined hypocenters is the same as would be observed if all earthquakes originated in the same point source. Therefore it is concluded that the Bucaramanga seismic source consists of a volume, less than 10 km in radius, centered at 6.8°N, 73.1°W., and 150 km depth.

A procedure for source studies from spectrums of long-period seismic body waves

The well-known first motion method of Nakano and Byerly is extended, generalized and combined with recent new ideas in body wave theory in order to set up a routine procedure for extracting source parameters from spectral analysis of isolated P and S pulses recorded at a net of standardized stations around a non-shallow source. The method consists of compensating the observed spectrums for instrumental and propagational effects. A combined study of the resulting radiation patterns, initial phases, and the initial amplitudes will render information regarding the spatial and temporal nature of deep and intermediate earthquake sources as seen through the spectral window of 10-100 seconds. The shorter periods can be used for source studies only if an accurate station correction is available.