FEATURE OF THE EARTHQUAKE SEQUENCES OF CENTRAL-SOUTH AMERICA

The location data of 10 earthquakes sequences of central-south America for the period 1960-1990 are collected. One of them is intraplate earthquake sequence and showed the feature:the major axis of the epicenter area is shorter, the ration of the major axis to minor axis is small. The other 9 sequences are interplate earthquake sequences occurred in the subduction zone and showed the common feature:the major axis of the epicenter area is longer, the depth of focus is 70km at most and is in the medium below crust(with the exception of the sequence No. 10), the fault plane solution of main shock in each scquence is controlled by the strike and dip of subduction zone. These sequences can be divided into two groups:group 1 includes 5 sequences of which the direction of major axis of the epicenter area is parallel to the strike of the subduction zone;group 2 includes 4sequences of which the direction of major axis of the epicenter area is perpendicular to the strikes of the subduction zone. For each sequence of group 1, ratio of the major axis of the epicenter area to the minor axis is larger;fault plane solutions of all aftershocks but a few early ones are not significantly different from that of the main shock. For group 2, ratio of the major axis of the epicenter area to the minor axis of some sequences is less;fault plane solutions of later aftershocks of a few sequences are significantly different from that of the main shock.