The relationship between seismicity and fault structure on the Discovery transform fault, East Pacific Rise

Abstract

There is a global seismic moment deficit on mid-ocean ridge transform faults, and the largest earthquakes on these faults do not rupture the full fault area. We explore the influence of physical fault structure, including step-overs in the fault trace, on the seismic behavior of the Discovery transform fault, 4S on the East Pacific Rise. One year of microseismicity recorded during a 2008 ocean bottom seismograph deployment (24,377 0 M L 4.6 earthquakes) and 24 years of Mw 5.4 earthquakes obtained from the Global Centroid Moment Tensor catalog, are correlated with surface fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 5.4 Mw 6.0 earthquakes that occurred on Discovery between 1 January 1990 and 1 April 2014 was relocated into one of five distinct rupture patches using a teleseismic surface wave cross-correlation technique. Microseismicity was relocated using the HypoDD relocation algorithm. The western fault segment of Discovery (DW) is composed of three zones of varying structure and seismic behavior: a zone with no large events and abundant microseismicity, a fully coupled zone with large earthquakes, and a complex zone with multiple fault strands and abundant seismicity. In general, microseismicity is reduced within the patches defined by the large, repeating earthquakes. While the extent of the large rupture patches on DW correlates with physical features in the bathymetry, step-overs in the primary fault trace are not observed at patch boundaries, suggesting along-strike heterogeneity in fault zone properties controls the size and location of the large events.

Earthquake Rupture in Fault Zones With Along‐Strike Material Heterogeneity

“…Yang et al (2014) detected damaged fault zones within the Anza gap and south of the Anza gap but not near the two ends of the Anza gap. A similar relationship between the spatial distribution of small earthquakes and damaged fault zones has also been observed in an oceanic setting, along the Discovery transform fault, East Pacific Rise (Froment et al, 2014;Wolfson-Schwehr et al, 2014).…”

Spatial and Temporal Variations in Earthquake Stress Drop on Gofar Transform Fault, East Pacific Rise: Implications for Fault Strength

“…RTFs have spatial and temporal patterns in seismicity that suggest varying mechanical properties (e.g., Kuna et al, ; McGuire et al, ; Wolfson‐Schwehr et al, ). On Gofar, coupling is determined seismically from a combination of long‐term global catalogs (e.g., Boettcher & Jordan, ; Boettcher & McGuire, ) and local OBS studies (McGuire et al, ).…”

The 2015 Mw 7.1 earthquake on the Charlie‐Gibbs transform fault: Repeating earthquakes and multimodal slip on a slow oceanic transform

“…McGuire et al . [] first observed quasi‐repeating sequences on fast‐slipping Pacific transforms, and this behavior has since been identified on the Blanco [ Braunmiller and Nábělek , ], Heezen [ Sykes and Ekström , ], and Gofar‐Discovery [ McGuire , ; Boettcher and McGuire , ; Wolfson‐Schwehr et al , ] fault systems. The maximum magnitude of these sequences ( M 5.4–6.4) scales with fault slip rate [ Boettcher and McGuire , ], and multiple cycles have been observed due to fast fault slip rates (6–14 cm/yr) and short repeat times (4–14 years).…”

“…McGuire et al . [] interpreted areas of heightened microseismicity between repeating earthquakes as “rupture barriers.” Factors including damage zone porosity [ Roland et al , ; Froment et al , ], enhanced fluid circulation [ Roland et al , ], and fault geometry [ Wolfson‐Schwehr et al , ] have been proposed to control this along‐strike variability in seismic coupling.…”