Seismicity properties of the Chain Transform Fault inferred using data
from the PI-LAB experiment
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 recorded on an array of ocean bottom
seismometers (OBS) 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 (MW ≥ 5.0) from global catalogs. We
divide Chain into three areas (eastern, central, and western) based on
multi-dimensional 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 MW ≥ 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. We find no evidence of
remote dynamic triggering and only weak evidence of tidal and static
stress triggering. Higher b-values are significantly correlated with
lower rMBA and also 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 MW ≥ 6.0 earthquakes are interrupted
by segments with abundant OBS activity but few historical events with
5.5 ≤ MW < 6.0. This segmentation is possibly
due to variable fluid circulation and alteration, which may also be
variable in time.