PMC

Topographic map of the Shillong Plateau showing major earthquakes (stars) M ≥ 7.0 including an 1897 great (M_s 8.7) earthquake. The focal mechanism of the 1897 earthquake is shown. The major tectonic features are also shown, such as DF: Dauki Fault; DT: Dapsi Thrust; OF: Oldham Fault; DuF: Dudhani Fault; KF: Kulsi Fault; BT: Barapani Thrust; BF: Brahmaputra Fault; NF: Naga Fault; D-KF: Dhansiri–Kopili Fault; SF: Sylhet Fault; UT: Ultapani Thrust; AF: Atherkhet Fault; EHZ: Eocene Hinge Zone and MBT: Main Boundary Thrust. The tectonic features are taken from the Geological Society of India, http://bhukosh.gsi.gov.in/Bhukosh/Public and from published literature. Triangles show the seismic station while red solid circles show the seismicity, used in the present study. Inset the location of the Shillong in the map of India (left panel) while right panel shows N–S section from Tibet to the Bay of Bengal showing the geometry of the plateau pop-up tectonic models proposed by (a) Bilham and England (2001) and (b) Kayal et al. (2012).

Normal stress changes (Δσ_n; bar, fault unclamping positive) created by the M_w7.2 and M_w7.4 earthquakes of 05 September 2004. Source faults of 2004 earthquakes are based on focal mechanism solutions available from USGS (https://earthquake.usgs.gov/earthquakes/eventpage/usp000d3ka/executive; https://earthquake.usgs.gov/earthquakes/eventpage/usp000d3mb/executive), and fault dimensions hinge on the empirical relationships of Wells & Coppersmith; stress is sampled at 7.5 km depth. The  rupture area of Baba et al. for the 1944 Tonankai earthquake (dashed black line) is shown for reference only. Symbols are as those in Fig. . This figure was generated using the Coulomb 3.4 software (https://earthquake.usgs.gov/research/software/coulomb) and Adobe Illustrator CS3 (https://www.adobe.com).

The structural map of the studied area shows different fault types and a variety of folds, including anticlines and synclines. The majority of anticlines and synclines exhibit a NW-SE orientation, which aligns with the main trend of the Zagros belt. However, the Sirwan syncline and Bamo anticline in the Middle and Southern segments do not coincide with the surrounding folds. The trend of the most thrusts is parallel with hinge line of the anticline.

Topographic map of the Lesser Antilles arc generated using Generic Mapping Tools (GMT) []. Red triangles denote active volcanoes. Limestone Caribbees are shown by the purple stippled line. The blue line shows the location of the trench. Green solid lines indicate oceanic fracture zones and continuing dashed lines show inferred projection of subducted fracture zones []. The black dashed line shows the subducted proto-Caribbean fracture zone []. The dashed red line shows the boundary between the proto-Caribbean and equatorial Atlantic seafloor []. The hashed region outlines the Tobago Terrane []. Orange line shows fault zones mentioned in the text: Southern Grenada Basin deformation front [], Hinge Line fault zone and North Coast fault zone []. Yellow stars highlight islands with reported meta-igneous cumulate xenoliths [–]. Yellow text represents ages of the oldest pre-Neogene volcanic rocks identified in the active arc (Grenada, Rojas-Agramonte, Williams []; Mayreau, Grenadines []; Martinique, Germa, Quidelleur []; and Dominica, Frey, Manon []).