Evidence for the release of long‐term tectonic strain stored in continental interiors through intraplate earthquakes

Abstract

The occurrence of large earthquakes in stable continental interiors challenges the applicability of the classical steady state “seismic cycle” model to such regions. Here we shed new light onto this issue using as a case study the cluster of large reverse faulting earthquakes that occurred in Fennoscandia at 11–9 ka, triggered by the removal of the ice load during the final phase of regional deglaciation. We show that these reverse‐faulting earthquakes occurred at a time when the horizontal strain rate field was extensional, which implies that these events did not release horizontal strain that was building up at the time but compressional strain that had been accumulated and stored elastically in the lithosphere over timescales similar to or longer than a glacial cycle. We argue that the tectonically stable continental lithosphere can store elastic strain on long timescales, the release of which may be triggered by rapid, local transient stress changes caused by surface mass redistribution, resulting in the occurrence of intermittent intraplate earthquakes.

Fluid Flow and Heat Transport Computation for Power-Law Scaling Poroperm Media

“…Laboratory experiments and numerical modelling identify strain levels of order ∼ 0.003 and above as creating an elastic damage within the crustal fabric [36]. At the same time, field data assess ambient crustal strain levels in the seismically inactive Fennoscandian crust of order ∼ 0.003 and above [37]. A binary population picture of crustal rock focused on cement-contacts is consistent with studies of the role cements play in crustal rock mechanics.…”

The April 2017 Mw6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids

“…The Botswana earthquake therefore did not require localized, present‐day, stress, or strain accumulation, contrary to plate boundary events resulting from the near‐fault accrual of stress imposed by plate and block motions (Kanamori & Brodsky, ). In a prestressed crust able to store reversible strain on long timescales (Craig et al, ; Feldl & Bilham, ) with faults at or close to failure (Townend & Zoback, ), short‐term fault strength transients, such as those triggered by fluids leaks from the upper mantle, may be all it takes to trigger large events.…”

Image log analysis of in situ stress orientation, breakout growth, and natural geologic structures to 2.5 km depth in central Scandinavian Caledonides: Results from the COSC‐1 borehole

“…The pattern of the strain rate field modeled by Craig et al . [] at 11–10,000 years does not look so different from the present‐day strain rate field calculated from geodetic observations [ Keiding et al , ], except that it is 1 order of magnitude lower today. However, the recent mapping of postglacial fault scarps in Sweden by Mikko et al [] shows a remarkably homogeneous NE‐SW orientation of these reverse faults that are consistent with the dominance of a linear rather than radial stress pattern in Scandinavia also at that time.…”