Seismicity Properties of the Chain Transform Fault Inferred Using Data From the PI‐LAB Experiment. Issue 3 (3rd March 2023)

• Record Type: Journal Article
• Authors: Leptokaropoulos, K.; Rychert, C. A.; Harmon, N.; Kendall, J. M.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-03
• Subjects: oceanic transform faults -- Mid Atlantic Ridge -- OBS seismicity -- fault segmentation -- seismotectonics; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024804
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Oceanic transform faults are intriguing in that they do not produce earthquakes as large as might be expected given their dimensions. We use 1‐year of local seismicity (370 events above M C = 2.3) recorded on an array of ocean bottom seismometers (OBSs) and geophysical data to study the seismotectonic properties of the Chain transform, located in the equatorial Mid‐Atlantic. We extend our analysis back in time by considering stronger earthquakes ( M W ≥ 5.0) from global catalogs. We divide Chain into three areas (east, central, and west) based on historical event distribution, morphology, and multidimensional OBS seismicity cluster analysis. Seismic activity recorded by the OBS is the highest at the eastern area of Chain where there is a lozenge‐shaped topographic high, a negative rMBA gravity anomaly, and only a few historical M W ≥ 5.5 events. OBS seismicity rates are lower in the western and central areas. However, these areas accommodate the majority of seismic moment release, as inferred from both OBS and historical data. Higher b ‐values are significantly correlated with lower rMBA and with shallower bathymetry, potentially related to thickened crust. Our results suggest high lateral heterogeneity along Chain. Patches with moderate to low OBS seismicity rates that occasionally host M W ≥ 6.0 earthquakes are interrupted by segments with abundant OBS activity but few historical events with 5.5 ≤ M W < 6.0. This segmentation is possibly due to variable fluid circulation and alteration, which may also change in time. Plain Language Summary: Oceanic transform faults (TFs) typically host earthquakes much smaller than expected based on their total seismogenic area. We study the seismotectonic properties of the Chain TF by combining 1‐year of seismicity recorded by an ocean bottom seismometer (OBS) array with geophysical data (bathymetry, tidal height, gravity anomalies). We supplement our analysis with strong historical earthquakes ( M ≥ 5.0) from global catalogs. Our analysis divides Chain into three areas: The east area is characterized by the highest OBS seismicity rates, negative gravity anomalies, large topographic highs, and few historical events with 5.5 ≤ M < 6.0. The west and central areas demonstrate lower OBS seismicity rates. However, they occasionally produce M ≥ 6.0, being responsible for most of the total seismic energy release. Higher numbers of stronger events occur in areas with negative gravity anomalies and shallower water depths. Our results suggest high lateral heterogeneity along Chain, with alternating seismic and aseismic patches, variable crustal thickness, different degrees of hydrothermal circulation/alteration, and potentially time‐dependent behavior. Key Points: Segmentation along Chain transform fault (Mid‐Atlantic Ocean) is studied by means of seismicity cluster analysis and geophysical data Chain demonstrates lateral heterogeneity with high moment‐release patches interrupted by segments with abundant but small magnitude events Spatiotemporal variations of seismicity are possibly manifested by variable hydrothermal circulation and alteration