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The Duality of Doublets: Unusually Large Aftershocks or Unusually Strong Fault Interactions?

Description: 

Earthquake doublets—large nearby events of similar size striking within a short period—have been a puzzle for over half a century. Is the second event in a doublet pair simply an unusually large aftershock, or do doublets reveal a unique fault interaction process? If all subduction zones exhibit the same percentage of doublets, that would support the first view. But if some subduction zones generate many more doublets than others, that would support the second view.

First, we find that doublets do indeed undergo Omori aftershock decay, reaching the background or steady doublet rate in 4-6 months, although the subsumed decay continues for much longer. However, among the world’s twelve major subduction zones, the Solomon-Vanuatu trench hosts ten times more doublets—defined arbitrarily here as M≥6 pairs within 0.25 M units, 50 km, and 10 years. Whether or not one normalizes by trench length and velocity, this difference cannot be explained by the 2-4 times higher rate of M≥6 shocks in the Solomon-Vanuatu trench. Here we argue that this extraordinary doublet rate results from abundant (near-vertical) tear faults in the slab and forearc. The trench produces seventeen times more doublets involving strike-slip motion than the mean of the other 11 major trenches. Coulomb stress transfer is as efficient between the subduction interface and adjacent tear faults as between megathrust surfaces offset by these tears. Tear faults segment and roughen the megathrust interface, hampering the along-strike propagation of great earthquakes, and so confine ruptures. As a result, the trench has an exceptionally low rate of M≥8 shocks despite a very high rate of M≥6 shocks. The seafloor roughness and tear faulting arise from the recent initiation and reorganization of subduction, and the entrainment of lithospheric fragments and rift-transform systems into the trench. The net impact is a higher post-mainshock hazard due to the abundance of doublets, but a lower rate of great earthquakes and the destructive tsunamis they generate.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond - III

Type: Oral

Date: 4/16/2026

Presentation Time: 05:00 PM (local time)

Presenting Author: Yu Jiang

Student Presenter: No

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