Barrier-Induced Rupture Front Disturbances during the 2023 Morocco Earthquake

Seismic waveforms, including teleseismic body waves, contain information about the irregular behavior of rupture propagation, which is essential for understanding the evolution process of large earthquakes. Here, a high-degree-of-freedom source inversion is applied to the teleseismic P waves of the 2023 moment magnitude 6.8 Morocco earthquake to reveal the irregular rupture behavior during earthquake growth. The resulting total moment tensor solution is an oblique focal mechanism that exhibits reverse faulting with a strike-slip component. There are two distinct peaks at 2 and 4 s in the moment rate function. The reverse fault component dominates at the beginning of the rupture, but then the strike-slip component increases to the second peak and then decreases. The main rupture propagates first in an east-northeast direction, then both up- and down-dip. The down-dip propagating rupture diminishes shortly, whereas the up-dip propagating rupture becomes dominant. The main rupture propagating in the up-dip direction is temporarily suppressed around a point located at 19 km depth and 10 km east-northeast of the hypocenter (region B). After the rupture propagates surrounding region B, the rupture propagates into region B, where a relatively fast slip rate is observed. It is confirmed that the irregular rupture propagation associated with region B is reproduced even when the model settings and the data sampling interval are slightly changed. The irregular rupture propagation obtained in this study suggests that a barrier with high apparent strength (e.g., high fracture surface energy) can cause the rupture to be initially suppressed within the barrier region, followed by delayed rupture propagation through the apparent barrier. The high-frequency seismic motions caused by such an irregular rupture propagation may have contributed to the increase in earthquake-related damage.