At 7:08 a.m. local time, the USGS's Hawaiian Volcano Observatory reported a 6.6 magnitude earthquake
just north of Kona Hawaii at 19.88°N, 155.935°W. At the time I was standing at 19.95°N, 155.861°W; essentially at the epicenter. The initial temblor was a violent shock wave followed by severe earth movement. I was standing outside my hotel at the time, having just finished a morning run when what sounded like a low flying 747 rocked the area. Except this was more like 10 jumbo jets at one time. The building was rocking as I saw the windows bow in and out. Paintings fell from the walls, power was cut, and a nearby gas line was leaking.
About 8 minutes later, a 5.8 magnitude quake struck the same area. It was about 20 minutes later that I finally found my wife who had been in our hotel room at the time. We decided to leave the hotel grounds by car to avoid any threat of a tsunami since the hotel was located at the coastline.
This area of Hawaii is the site of the upcoming Ironman Triathlon. If you've seen photos, you know that there is essentially nothing but lava flows (both aa and pahoehoe for you geologists) along most of this part of the Kohala coast. Many roads were littered with small to car-sized bolders but were passable. We headed toward Waimea about 10 miles away at about 2500 feet of elevation. As radio reports from the Pacific Tsunami Warning Center
indicated no tsunami threat we headed back to the hotel.
Two hours after the first earthquake, a third 4.8 earthquake shook the region which only served to unsettle everyone who had hoped things were quieting down.
From a geologic and geospatial perspective, this was an unusual quake. As a geologist, I had thought that I understood about the threat of major earthquakes being pretty low. Many of you are probably familiar with the geology of Hawaii but let me refresh your memory. The island chain sits on an intraplate hotspot. As the Pacific plate moved over time, each island was formed due to the eruption of volcanoes forming new land masses. The Big Island, where the quakes occurred, is home to Mauna Kea, the highest mountain in the world from base to peak. But this is not the site of subduction zones where most seismic activity occurs, especialy large earthquakes. That's why this was such an unusual occurrance. These volcanoes are termed "shield" for the gradually sloping, canonical shapes that do not generally erupt violently.
With many major aftershocks, it was interesting to hear the explanation of what caused the quakes. No official word from the USGS has been announced as yet.