Crustal Motions Observed from GPS Observations for the M6.9 Earthquake in Hawaii and the Eruption of the Kilauea Volcano in 2018

In 2018 the Kilauea volcano erupted and on May 5, an earthquake of M6.9 occurred in Hawaii. Though the methods used by the authors to get the results in the regional reference frame and the methods for NA12 results are different in some way, both results for NA12 are in good agreement. The results in NA12 at GPS continuous observation stations, directly obtained from http://geodesy.unr.edu, were analyzed to show crustal motions in Hawaii. The preseismic crustal movements were dominated by deformation precursory to the earthquake while the influence of the volcanic eruption was secondary. The coseismic displacements were the result of the rupture of the earthquake fault. The post seismic displacements around the crater were quite large but localized in a rather small area. No accumulated preseismic vertical displacements were observed near the epicenter. The coseismic horizontal displacements were instant and dramatic displacements in opposite sense to the accumulated preseismic horizontal displacements so they were elastic rebound of the accumulated preseismic horizontal displacements. Therefore, the accumulated preseismic horizontal displacements were precursors to the earthquake. In comparison to other large earthquakes, the media of a quite small area around the epicenter was nearly elastic. The crustal movements near the epicenter, imminent to the earthquake were quite significant. They showed the preslip of the earthquake fault or preseismic displacements. This earthquake is a special case that showed the existence of imminent deformation precursory to the earthquake. They are new clues for the future observations and study on the imminent precursors. The M6.9 earthquake in Hawaii was the result of compression of the crust of the island by horizontal motion in NW direction before the earthquake, which led to shear rupture of the earthquake fault that caused the earthquake. This fact is in good agreement with the model of rebound or elastic rebound proposed by the authors, the compression-shear model of rebound or elastic rebound, that is, the model of preseismic compression that leads to shear rupture of the earthquake.