The 2018 Mw6.4 Hualien earthquake: Complex rupture process of a moderate event

High-angle oblique subduction generally produces trench-parallel fault system, which accommodates the thrusting and lateral-shearing strains on the slab interface and the strike-slip faults, respectively. Slip partitioning of such fault systems generally occurs as thrust and strike-slip earthquakes separately. The Meilun Fault, located on the east coast of Taiwan, is one example of such fault system. During the 6 February 2018 Mw6.4 Hualien earthquake, the Meilun Fault was ruptured with 1 m of offset. Ground deformation observed near the Meilun Fault indicates that co-seismic slips are partitioned as strike-slip motion on the Meilun Fault and thrust motion on an off-shore thrust fault. We conducted finite-fault inversion using regional geodetic data, multi-point source inversion using teleseismic and regional strong motion data, and analyzed aftershock locations to determine the fault geometry. These analyses consistently support that both the slab interface and the Meilun Fault ruptured during the dynamic rupture process.

Joint inversion of teleseismic, regional strong motion and geodetic data was also preformed to image the kinematic rupture process. Results clearly reveal a dynamic slip partitioning process: the rupture was initiated on the slab interface with an oblique strike-slip motion and then jumped to the Meilun Fault. Slips on the Meilun Fault were dominated by a left-lateral strike-slip motion, though its southern end contains a significant normal-faulting component. Given the moderate magnitude, the Hualien earthquake exhibits and unusually complicated rupture process with thrusting, strike-slip and normal faulting slips.