EN-ECHELON RUPTURES DURING THE GREAT BOLIVIAN EARTHQUAKE OF 1994

Rupture during this event has two characteristics. First bursts of major moment release (subevents) have a component of eastward movement from the epicenter. Second, later subevents show northward directivity. These observations lead to a model with four subevents, the latter three being line sources Propagating within approximately +/-30 degrees of north. This model has en echelon regions of moment release over sub-horizontal plane(s) and rupture speeds up to 3.5+/-0.5 km/s within subevents. Moment release over en echelon regions can accommodate high moment release over a limited seismogenic volume within subducted lithosphere. Depending on the exact geometry of the Wadati-Benioff zone and the precise direction of rupture propagation, lower bounds on the thickness of the seismogenic zone during this event range approximately 10-40 km. While several aspects of the en echelon rupture model dovetail with predictions based on the anticrack model for deep-focus seismicity, one must also allow for the possibility that the rupture zone extended beyond the expected thickness of metastable olivine wedge.