VOLCANO WATCH: Hawai‘i Island Still Rocks

On July 18, 2014, newspapers across the United States published a story titled “Quake risk rises for much of US.”

Hawaii was listed among the 16 states facing the highest risk for earthquakes. What’s more, the story listed the Island of Still as one of the biggest hazard areas.

The point of the July 18 article was to announce the release of the US Geological Survey National Seismic Hazard Mapping Project’s (NSHMP) updated seismic hazards map of the conterminous 48 states. Plans for updating the hazards maps for Alaska and Hawaii are underway.

For decades, using methodologies known as probabilistic seismic hazards modeling, the NSHMP has produced models showing how strong earthquake shaking will affect areas of the country within specified time intervals. The models are used in a number of public policy areas, including building codes, risk assessments, and insurance-rate structures.

The 2014 updated seismic hazards maps incorporate recent research findings of active faults and fault measurements, earthquake activity, strong ground shaking, and methodologies for computing seismic hazards. Every large earthquake — even those in other countries, such as Japan’s 2011 magnitude-9 Tohoku earthquake — provides new and important observations and data.

The NSHMP typically performs the calculations underlying the probabilistic maps, and much of this research has been supported or performed by the USGS. Engaging local experts and stakeholders and achieving consensus regarding input to the model calculations are also critical to producing useful hazards maps.

We have been fortunate that significant earthquake losses in Hawaii have not occurred since the Kīholo Bay and Māhukona events (magnitudes 6.7 and 6.0, respectively) in 2006. Besides reminding us that large, damaging earthquakes are not restricted to the flanks of active volcanoes on the Island of Hawai‘i, the 2006 earthquakes provided important lessons and data that are shaping current thought and effort.

Important data for understanding the strong ground shaking that caused most of the observed earthquake damage in Hawaii in 2006 came from roughly two dozen USGS strong-motion accelerographs operated in fire stations, hospitals, and other public building across the County of Hawai‘i.

The USGS Hawaiian Volcano Observatory (HVO) assisted in a FEMA-sponsored project to measure geophysical properties that influence strong shaking, such as that recorded in 2006. Two subsequent USGS-supported research projects developed equations for predicting strong ground shaking in Hawaii from future damaging earthquakes here.

The uses of these research results extend beyond probabilistic seismic-hazards mapping. A ground-motion prediction equation from one of these studies in 2010 has been incorporated into the USGS ShakeMap utility. ShakeMaps have proven themselves useful in both post-event assessments and earthquake-scenario planning.

As one of the USGS’s volcano observatories, HVO dedicates its seismic-monitoring efforts to the abundant microseismicity accompanying active volcanic processes culminating in eruptions. Because it maintains the largest USGS seismic-monitoring network in Hawaii, HVO is also responsible for cataloging all significant earthquakes in the state.

The USGS performance assessment after the 2006 Kīholo Bay and Māhukona earthquakes led to significant upgrades to both HVO’s infrastructure for seismic data analysis and its field network of instruments. Since initial installation and implementation, these continue to offer improved capabilities.

Let’s all look ahead to Hawaii’s updated seismic-hazards maps and be among the nation’s most prepared and informed states about earthquake hazards. Watch for information about the Oct. 16, 2014, Great Hawaii ShakeOut in future Volcano Watch articles. Don’t freak out, shake out!

Kīlauea activity update

Kīlauea’s summit lava lake within Halema‘uma‘u produced nighttime glow that was visible via HVO’s Webcam over the past week. The lava lake level was relatively steady, hovering around 35 m (115 ft) below the rim of the Overlook crater.

On Kīlauea’s East Rift Zone, the June 27 flow from Pu‘u ‘Ō‘ō’s northeast flank continued to advance slowly toward the northeast, reaching to about 4.4 km (2.7 miles) from the vent by mid-week. Three small lava ponds were active on the Pu‘u ‘Ō‘ō crater floor for at least part of the week.

No earthquakes were reported felt during the past week in Hawaii.

Visit the HVO website for Kīlauea, Mauna Loa, and Hualālai activity updates, recent volcano photos, recent earthquakes, and more; call 967-8862 for a Kīlauea summary; email questions to askHVO@usgs.gov.

Volcano Watch is a weekly article and activity update written by scientists at the US Geological Survey`s Hawaiian Volcano Observatory.