Seismic velocity structure of the easternmost segment of the Gofar transform fault, East Pacific Rise
The fast-slipping (~ 14 cm/yr) Gofar transform fault (GTF) East Pacific Rise has three active segments G1 to G3 from east to west. These fault segments produce large earthquakes (MW ~ 6.0) quasi-periodically every five to six years (Figure 1). Interestingly, large earthquakes rupture the same 20-km long fault patches separated by a ~ 10-km rupture barrier zone, implying along-strike variations in fault zone material properties (McGuire et al. 2012). This further suggests that rupture patches and barrier zones remain stable over multiple seismic cycles. Here, we jointly invert P- and S-wave travel times, recorded at an ocean-bottom-seismometer (OBS) experiment along G1 between January 2019 and February 2020, to determine the 3-D seismic velocity structure of the area and relocate the local earthquakes. Our velocity models reveal a large low-velocity anomaly extending through the entire oceanic crust along G1 with some along-strike variations. We identify a 10 km-long rupture barrier zone, which is interpreted to be highly fractured with enhanced fluid circulation. We further suggest that the observed deep seismicity underlying the rupture barrier zone may indicate sea-water infiltration. Lastly, we apply the same approach to the westernmost segment of the GTF and observe some similarities and differences between the two fault zone seismic velocity structures.