Crustal earthquake triggering by modern great earthquakes on subduction zone thrusts

摘要

Among the many questions raised by the recent abundance of great (M>8.0) subduction thrust earthquakes is their potential to trigger damaging earthquakes on crustal faults within the overriding plate and beneath many of the world’s densely populated urban centers. We take advantage of the coincident abundance of great earthquakes globally and instrumental observations since 1960 to assess this triggering potential by analyzing centroids and focal mechanisms from the centroid moment tensor catalog for events starting in 1976 and published reports about the M9.5 1960 Chile and M9.2 1964 Alaska earthquake sequences. We find clear increases in the rates of crustal earthquakes in the overriding plate within days following all subduction thrust earthquakes of M>8.6, within about ±10° of the triggering event centroid latitude and longitude. This result is consistent with dynamic triggering of more distant increases of shallow seismicity rates at distances beyond ±10°, suggesting that dynamic triggering may be important within the near field too. Crustal earthquake rate increases may also follow smaller M>7.5 subduction thrust events, but because activity typically occurs offshore in the immediately vicinity of the triggering rupture plane, it cannot be unambiguously attributed to sources within the overriding plate. These observations are easily explained in the context of existing earthquake scaling laws.