Da. Wiens et Jj. Mcguire, THE 1994 BOLIVIA AND TONGA EVENTS - FUNDAMENTALLY DIFFERENT TYPES OF DEEP EARTHQUAKES, Geophysical research letters, 22(16), 1995, pp. 2245-2248
The 1994 Bolivia and Tonga events show large differences in source and
aftershock properties. The Bolivia earthquake, characterized by high
stress drop, slow rupture propagation, and a weak aftershock sequence,
appears similar to other large deep earthquakes that are isolated fro
m active seismic zones, including the 1970 Colombia earthquake. In con
trast, the 1994 Tonga event showed stress drop, rupture propagation ve
locities, and an aftershock sequence similar to that found for shallow
earthquakes. The aftershock sequence of the 1994 Tonga event is many
times stronger than has been observed for any other deep earthquake. A
survey of deep earthquake aftershocks suggests that aftershock occurr
ence is correlated with the overall subduction zone magnitude frequenc
y relation (b-value). The largest deep events occur in isolated region
s lacking smaller earthquakes, or in subduction zones characterized by
anomalously low b-values. The 1994 Tonga event is an exception and is
the largest deep earthquake to occur within an active subduction zone
showing a large b-value, perhaps explaining the strong aftershock seq
uence. The Bolivia and Tonga events may represent end members of a pop
ulation of deep earthquakes showing exceptional diversity in source pr
operties, or they may represent two fundamentally different types of d
eep earthquakes, perhaps resulting from different physical mechanisms.