Fig. 2: Distribution of earthquakes and focal mechanisms.
From: Microseismicity and lithosphere thickness at a nearly-amagmatic oceanic detachment fault system
a Bathymetric map of the SWIR 64°30’E area showing 307 events of the SMSMO (blue circles) and RVSMO (orange circles) catalogs, the RVSMO seismic swarm (green circles), and 8 determined focal mechanisms. Cross in the legend shows the average absolute horizontal location uncertainty of 3.2 km (1σ). Geological information (see legend for symbols) includes breakaways, emergences, and the boundary between volcanic and smooth seafloor1. Best-fitting focal mechanisms have clear upward (black dots) and downward (white dots) first motions of P-wave onsets (see the “Methods” section). Depth profiles (P0–P0’ to P3–P3’) are marked as labeled white lines in a. b Histograms of earthquake depths below the seafloor for the SMSMO (blue) and RVSMO (orange) catalogs, including the seismic swarm (green). c Along-axis depth profile P0–P0’ projecting earthquakes within ±8 km off the profile (VE = 1 and the same below). The vertical bar shows the average absolute vertical uncertainty of 2.8 km (1σ). The classification of volcanic (pink) and smooth (blue) seafloor is indicated4. Gray dashed line is the 7.5 km/s velocity contour39. Labeled gray dashed lines show depths below the seafloor (the same below). d and e Across-axis depth profiles P1–P1’ and P2–P2’ projecting earthquakes within ±3 km off the profiles. Black dashed lines indicate the fault plane adapted from (f). f Across-axis depth profile P3–P3’ projecting earthquakes within ±5 km off the profile. Dotted lines represent seismic reflectors, interpreted as DF1 damage zone23, with the main detachment fault plane tentatively drawn in the center (subseafloor solid black line). Black23 and gray39 dashed lines are the 7.5 km/s velocity contours. Focal mechanisms are projected to profiles P2–P2’ and P3–P3’.
