Fig. 1: Seismicity along Chain transform fault.

a Bathymetric map of the study area with the four topographic highs, i.e., the western flower structures (WSF) and the Eastern Large Flower Structure (ELFS), all represented as yellow curves. The red and green curves show the fault scarps, with the latter highlighting the longest of them (L > 30 km). We use an oblique Mercator projection so that the transform appears horizontal, which is the reason for angled ticks marking longitude and latitude. High quality focal mechanisms calculated from the Ocean Bottom Seismometer (OBS) data projected as lower hemispheres. Events with dominant reverse and normal components are indicated by green and red beachballs, respectively. Inset map shows the study region (red box). OBS stations are shown by green triangles. Horizontal resolution of the bathymetry is 100 m and vertical resolution is ~10 s m. b Seismicity epicenters in the OBS data superimposed over the residual mantle Bouguer anomaly (rMBA) values in the study area. Black and white dots indicate events along the transform valley, located on high rMBA (>−3 mgal) and low rMBA (<−3 mgal), respectively. c Histogram with the number of OBS earthquake events per 0.05° longitudinal bins. The blue and red circles show the historical events with M_W ≥ 5.6 and M_W ≥ 6.0, respectively³¹. The number in the arrows show the seismically released moment fraction for these segments (Methods). The black curve shows along strike variation of b-value in Chain, considering equally sized event windows of 75 OBS events each, advancing by 1 event and the standard error of b-value is defined by the purple area. The horizontal blue lines at the x-axis indicate the location of the positive flower structures. The shaded areas correspond to asperities (A1 and A2) which separate the barriers (B1, B2, B3). d Along-strike cumulative seismic moment of the historical events (black line). The other panel features as in c.