When seismologists Fred Klein and Steve Kirby began studying the devastating earthquakes of Oct. 15, they initially found no link to previous deep quakes.

And then they found the connection. All these temblors were scattered around and centered on Mauna Loa, the world's largest volcano.

"If you plot a map and plot compression directions, they all make little arrows that point to Mauna Loa," said Klein, a former Hawaiian Volcano Observatory scientist who now works with Kirby at the U.S. Geological Survey at Menlo Park, Calif.

Klein said the result of his study is chilling: These quakes don't give notice. They can occur any time, on any side of the Big Island. Having had one recently doesn't mean underground stress is relieved — there can be decades between quakes, or minutes.

And while these very deep earthquakes are not known for producing large tsunami, their shaking can be felt for great distances and can cause significant damage on land, as the October earthquakes did.

"The October quakes forced us to go back and look at the history of earthquakes in Hawai'i," said Ed Teixeira, state deputy director for civil defense. "From a historical perspective, all of us tend to lose sight of these. If it's a generation between events, you lose institutional memory."

He said civil defense officials are arguing in this year's Legislature for a statewide building code, to help the state have a consistent construction policy which can ensure that new buildings are made to help occupants survive the effects of earth-quakes.

Klein's study will be presented today as part of the annual meeting of the Seismological Society of America. More than 400 seismologists are on the Big Island this week discussing the latest research into causes and effects of earthquakes.

Today's session at the Hilton Waikoloa Village will be devoted to papers on the Oct. 15 quakes, which stunned the state and caused an estimated $200 million damage to Big Island homes, businesses and public facilities.

The quakes came from areas not previously known for strong earthquakes. Deeper than standard volcano-related quakes —one 24 miles deep and one 11 miles down — they were felt statewide.

The larger quake, a 6.7-magnitude shaker under Kiholo Bay on the Big Island, was the strongest quake in the nation in 2006.

It knocked down buildings and damaged others, primarily on the Big Island. The Mauna Kea Beach Hotel remains closed for repairs. Roads and drainage systems were cracked.

Dozens of homes were declared uninhabitable. Emergency radio stations were off the air. Roads and bridges were closed on Maui. Much of Honolulu was without power for most of the day. Homes rocked even on Kaua'i, 300 miles away.

The deep earthquakes occur in the brittle outermost part of the Earth's mantle, the largest proportion of the planet that sits between the thin crust of the earth and the core. In ocean areas, that's from just a few miles below the sea floor to 1,800 miles below the surface.

The Big Island deep quakes, which range from 11 to 24 miles below the surface, occur in a region of the mantle that is being "bent" by the immense weight of Mauna Loa — the most massive of the Hawaiian volcanoes.

That bending force puts great pressure on the rocks of the mantle, which occasionally slip against each other, causing earthquakes. Klein compares the action to pressing your dry palms firmly together and forcing them in opposite directions until they slip. When rocks do that underground, the violence of the action sends out shock waves in the form of earthquakes.

Hawaiian Volcano Observatory chief Jim Kauahikaua said the weight of the mountain continues to cause the flexing of the sea floor.

"The Big Island is sinking faster than the rest of the state," he said.

Kauahikaua said the larger October quake did cause a small tsunami, but more powerful locally generated tsunamis tend to be produced by a different and shallower kind of earthquake — the "decoullement" type, in which volcanic rock slips horizontally across the Earth's crust. The Nov. 29, 1975, earthquake, whose tsunami swept through a group of campers at Halape, was one of these.

Civil defense officials were criticized after the Oct. 15 events because many residents feared a devastating tsunami had been generated. However, officials thought sending a message using the words "no tsunami" would cause confusion, so no such alert was sent out.

While there are many smaller upper-mantle earthquakes than the October events, there have been only nine such quakes in the past 130 years with magnitudes of 6.0 or stronger. Before the two in 2006, the previous one was off Honomu in 1973, and before that south of Kilauea in 1955.

Among the nine big, deep quakes that science knows about, the shortest time between them was the 15 minutes between the October quakes. The longest has been the 56 years between 1885's Honomu quake and 1941's Kohala quake.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.