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° 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.