Slip on ridge transform faults : insights from earthquakes and laboratory experiments

Abstract

The relatively simple tectonic environment of mid-ocean ridge transform fault (RTF) seismicity provides a unique opportunity for investigation of earthquake and faulting processes. We develop a scaling model that is complete in that all the seismic parameters are related to the RTF tectonic parameters. Laboratory work on the frictional stability of olivine aggregates shows that the depth extent of oceanic faulting is thermally controlled and limited by the 600°C isotherm. Slip on RTFs is primarily aseismic, only 15% of the tectonic offset is accommodated by earthquakes. Despite extensive fault areas, few large earthquakes occur on RTFs, and few aftershocks follow the large events. Standard models of seismicity, in which all earthquakes result from the same seismic triggering process, do not describe RTF earthquakes. Instead, large earthquakes appear to be preceded by an extended fault preparation process marked by abundant foreshocks within 1 hour and 15 km of the mainshocks. In our experiments normal force vibrations, such as seismic radiation from nearby earthquakes, can weaken and potentially destabilize steadily creeping faults. Integrating the rheology, geology, and seismicity of RTFs, we develop a synoptic model to better understand the spatial distribution of fault strength and stability and provide insight into slip accommodation on RTFs.

Segmentation of the Blanco Transform Fault Zone from earthquake analysis: Complex tectonics of an oceanic transform fault

“…The average seismic zone width is 7.0 (8.7) km assuming seismic slip is confined between the 200°C (100°C) and 600°C isotherms. The 100°–200°C temperature range corresponds to the transition from aseismic stable sliding at shallow depth to deeper stick‐slip behavior in serpentinite [ Moore et al , 2004; Boettcher , 2005]. The only significant deviation from the isotherm‐based cutoff appears to occur for the M w = 6.5, 27 October 1994 event (large ellipse in Figure 14, middle); for this large event, a circular rupture assumption is likely incorrect and the actual rupture probably had a large length‐to‐width ratio with significant slip along most of the western Blanco Ridge.…”

Absolute Centroid Location of Submarine Earthquakes from 3D Waveform Modeling of Water Reverberations

“…Different from their continental analogues, OTFs have a simple geometric configuration, a close to homogeneous composition and a smooth thermal structure (Fox & Gallo, 1984;Turcotte & Schubert, 2014;Wilson, 1965). This relative simplicity leads to a somewhat predictable seismic behavior that is less dependent on the geologic history of the plate boundary, allowing us to dissect the different thermal-mechanical factors that control earthquake rupture along transform faults Boettcher (2005). However, despite the substantial attention that OTFs have received, there are still many of their seismological aspects that are not well understood, especially on a global scale.…”

Tectonic Processes in the Jan Mayen Fracture Zone Based on Earthquake Occurrence and Bathymetry

“…Assuming full coupling, the expected recurrence interval for events of 6 along a 10 10 km fault patch for a range of stress drops was calculated, assuming a spreading rate of 16 mm/yr and that slip scales as the square root of the rupture area (M. Boettcher, personal comm., 2006). The results indicate that a recurrence interval of 10-15 years would give full seismic coupling on a fault patch for earthquakes with stress drops of 0.5-1 MPa, which is in the range of stress drops found on ridge transform faults (Boettcher and Jordan, 2004;Boettcher, 2005). This is an interesting result because it implies that a particular fault patch is fully coupled, while the surrounding fault area is probably slipping predominantly aseismically.…”