ABSTRACT

I review the unusual swarm of 50 earthquakes, Mw 5.2–5.4, which occurred at Kīlauea caldera between May and August 2018. Given the strong similarity in published source mechanisms derived by centroid moment tensor (CMT) methods, I stacked the P waves from a global distribution of stations from local to antipodal distances. The composite source mechanism is consistent with a normal planar fault striking 335° NNW, dipping 78° W, with a rake nearly 90°. The differences between the composite source and waveform‐derived sources are due in part to the choice of source depth, seismic velocity, and rigidity beneath Kīlauea summit. Antipodal PKIKP observations of the bottom of the source are derived from stacked data from three Global Seismographic Network (GSN) stations at 175°Δ in southern Africa. The stacked PKIKP displacement data show dilatational first motions, apparently inconsistent with proposed piston models of the volcano–earthquake activity for comparable swarms observed in the Galapagos, Miyakejima, and Iceland. As recognized in these prior studies, the vertical‐P compensated linear vector dipole (CLVD) moment tensor solutions likely result from arcuate faults, which collectively circumscribe the caldera. The interevent times of the swarm sequence are not random; rather, the time interval between events increases by 1/2  hr for each earthquake.

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