Seismic sensors & networks paul okuboPresentation Transcript
Seismic sensors and networks: Hawaii Earthquake Preparedness Workshop La Serena, Chile December, 2007 Paul Okubo, Geophysicist Hawaiian Volcano ObservatoryU.S. Department of the InteriorU.S. Geological Survey
Hawaii: volcanically and seismically active Active subareal shield volcanoes: (1) Kilauea and (2) Mauna Loa 3 Active fault systems in volcanic edifice and in lithosphere In October 2006, M6.7 lithospheric earthquake (3) and 2 1 aftershock sequence, caused widespread damage, including some to Mauna Kea telescope facilities Though not a problem in 2006, additional concern regarding locally-generated tsunamis associated with crustal earthquakesEarthquakes M>1.3, located by USGS Oct 2006 – Nov 2007
A number of instrument types operated by a number of groups
HVO’s short period stations•Real time telemetry/near-real-time analysis•Microearthquake detectionand location on volcanoes•Narrow band and limiteddynamic range, typically clipon large events•Relatively inexpensive: manystations to monitor a largearea. -HVO short period vertical component -HVO short period multicomponent -HVO broadband multicomponent -HVO accelerometer -HVO future broadband -Borehole sites -NSMP digital strong motion sites -PTWC -IRIS (1 big island, 1 Oahu)
VOLCANO MONITORING Pu’u O’o fountain episode in 1984 By tracking microearthquake hypocenters occurring in swarms on the active volcanoes, it is possible to infer the location of the active dike. For example, the apparent downrift migration of epicenters shown above allowed volcanologists to deploy in time to see the start of Kilauea’s east rift zone eruption in 1983.
USGS (HVO and NSMP)broadband and accelerometerstations-Improved data quality-Record a wider range offrequencies.-Stay on-scale during largeearthquakes.-Mix of real-time and polledsystems-Require greater telemetrybandwidth/power, generally morecostly. -HVO short period vertical component -HVO short period multicomponent -HVO broadband multicomponent -HVO accelerometer -HVO future broadband -Borehole sites -NSMP digital strong motion sites -PTWC -IRIS (1 big island, 1 Oahu)
Hawaii Earthquake HistoryLarge earthquakes in Hawaii have beenrecorded throughout its written history,dating back to 1823.The 19th century seems appears to havebeen more seismically active than the 20thCentury, but,With the connection of seismicity to activevolcanism. There is no reason to think thatHawaii will not have future large - andpotentially devastating earthquakes. Church damaged by October 2006 earthquakes Figure adapted and updated from Wyss and Koyanagi, 1992
From: Klein and Kirby, 2007
Hawaii Probabilistic Seismic Hazard Map http://earthquake.usgs.gov/research/hazmaps/products_data/Hawaii/
Stations operated by otheragencies, data shared with HVO.Data imports and exports viadedicated links and internet.Expand and improve monitoringscope beyond the activevolcanoes.HVO data shared in return,principally to Pacific TsunamiWarning Center on island ofOahu. -HVO short period vertical component -HVO short period multicomponent -HVO broadband multicomponent -HVO accelerometer -HVO future broadband -Borehole sites -NSMP digital strong motion sites -PTWC -IRIS (1 big island, 1 Oahu)
Large Earthquakes and Tsunamis Earthquakes in 1868,1908,1951, and 1975 produced tsunamis; Special concern for tsunamigenic event occurring on western coast of island - exposure to Honolulu and other islandsFrom: Klein and Kirby, 2007 Home along SE coast, washed off its foundation and 25 m inland by 1975 tsunami
Seismic monitoring in Hawaii - recent incentives • December 2004 Sumatran earthquake and Indian Ocean tsunami tsunami monitoring upgrades for NOAA and USGS GSN - teleseismic and local major goals: report local earthquake location and magnitude within 90s of event origin time and issue tsunami bulletin within 5 minutes • October 2006 Island of Hawaii earthquakes USGS operational upgrades major goals: improved earthquake reporting products generation and delivery
Coordinated seismic monitoring in Hawaii - goals Monitoring activities cover earthquakes, volcanoes, tsunamis, and landslides Operate a reliable and robust statewide system to record earthquake ground motions over the relevant range of frequencies and shaking levels Distribute clear, reliable information about earthquakes and their effects rapidly after their occurrence for emergency response and public information Create an easily accessible archive of Hawaii earthquake data and information - including waveform data and derived products - for engineering and scientific applications and research
Establish modern, State-wide seismic monitoring capabilities withcontinuous data collection and exchange
ANSS - Advanced National Seismic SystemOperated and managed by the USGS;Groups seismic monitoring activities in the United States into seven (7) ANSS US Regions: Northeast US; Central and Eastern US; Intermountain West; California; Pacific Northwest; Alaska; Hawaii ; and Puerto Rico and US Trust Territories. The USGS and its supported networks are responsible for earthquake reporting in the US (based on NEHRP legislation and “Stafford Act”).
Earthquake early warningOperational early warning systems exist in Japan, Mexico,Romania, Taiwan and Turkey.In the US - spearheaded in California by the CaliforniaIntegrated Seismic Network partners, including the USGS -early warning systems are being developed and tested.Systems can be characterized as network-based or onsitewarning systems.
Earthquake early warning in Hawaii for Mauna Kea telescopes?Simple considerations from actual earthquakes:1. 1975 Kalapana M7.2 earthquake on SE coast of Hawaii Island P-wave propagation time to closest seismic station = 2.05s P-wave propagation time to Mauna Kea (Hale Pohaku) = 11.40s S-wave propagation time to Mauna Kea approx. 20 s2. 2006 Kiholo Bay M6.7 earthquake off NW coast of Hawaii Island P-wave propagation time to closest station = 6.77s P-wave propagation time to Mauna Kea = 9.22s S-wave propagation time to Mauna Kea approx. 16 s
Earthquake early warning in Hawaii for Mauna Kea telescopes?Very preliminary thoughts:Time frame for first registration of earthquake signals can be reducedby increasing seismographic network density, essentially put stationscloser to possible earthquake locations.There might be approximately 20 s between first recognition of alarge earthquake and the onset of strong shaking at Mauna Kea, longerintervals for earthquakes occurring in more distant Hawaii source regions.Draw from experiences of early warning systems and efforts in other parts of theWorld, and, depending on assets and resources, implement or adapt for Hawaii.Use historical record and seismic hazards modeling to help with design andconstruction.