The Earthquake of 1975
Apr 20, 2009 I Earthquakes.Wednesday, November 29, marks the 20th anniversary of the 1975 Kalapana earthquake, the largest earthquake to strike Hawaii since 1868. Residents were awakened at 3:35 a.m. by a magnitude-5.7 earthquake located a few miles inland of Lae’apuki on Kilauea’s south coast. A little more than one hour later, at 4:47 a.m., the main shock struck with a magnitude of 7.2. The epicenter was located at Kamoamoa, just a few miles east, and closer to the shoreline, from the foreshock.
Much of the south coast of Hawaii Island slid horizontally towards the ocean and subsided. The maximum horizontal displacement, near Keauhou Landing several kilometers east of Halape, was about 26 feet. The displacements decreased to the east and west from this area.
Similarly, subsidence of the coast was greatest in this same area and amounted to about 11.5 feet. The amount of subsidence rapidly decreased to the west, and, at Punalu’u, the shoreline actually uplifted by about 4 inches. To the east, subsidence was about 9.8 feet at Halape, 3.6 feet at Kamoamoa, 2