Fig. 4

Fault-plane solutions based on first-motion polarities for 8 earthquakes in 2017 (see Additional file 1: Table S4). All stereograms are lower hemisphere, equal-area projections. Solid circles correspond to compressive first motion (up); empty circles correspond to dilatational first motion (down). The take-off angles were computed with the NonLinLoc software (Lomax et al. 2000), using the 3D velocity model of Husen et al. (2003). Grey lines show sets of acceptable solutions derived by the HASH algorithm (Hardebeck and Shearer 2002); black bold lines indicate the (preferred) average focal mechanisms of all accepted solutions; red bold lines mark the active plane as determined from high-precision relative earthquake relocations, where available. Information on origin time (UTC time), focal depth in km below mean sea level (Z), region (same label as in Fig. 2 and Additional file 1: Table S4) and the two focal planes (defined by strike, dip, rake) is provided above and below each mechanism. See text for definition of strike, dip and rake