Tsunami Warning System Overview and Seismic Data Acquisition

1. U. Washington Tsunami Certificate ProgramCourse 2:Tsunami Warning SystemsSession 1Tsunami Warning System Overview and Seismic Data AcquisitionJuly 25, 2007 1:15-2:45pm Page 1

2. Outline • Part 1 – TWS Overview • Tsunami Warning Systems • History • Philosophy • Challenges • Warning Center Functions • Part 2 – Seismic Data Acquisition • Seismometry • Networks • Station Distribution • Exercise Page 2

3. Part 1 - Tsunami Warning Systems - History in the United States • 1949 Honolulu Observatory established • Co-located with existing Magnetics Observatory • Used data sent via teletype from seismic observatories • Established in time for major tsunamis of the 50s/60s • 1967 Alaska Tsunami Warning System established • Followed tsunami destruction due to 1964 Gulf of Alaska earthquake • Originally 3 centers; later combined into 1. • 1968 Pacific Tsunami Warning Center established • Officially expanded scope of Honolulu Observatory to other nations Page 3

4. Tsunami Warning System History in the United States Page 4

5. Tsunami Warning Systems • Non-U.S. Centers • Japan • Russia • French Polynesia • Chile • Systems developing as a result of 2004 Indian Ocean Tsunami • For example; Australia, Thailand, Indonesia, … • Caribbean • Conclusion • Devastating Tsunami leads to Establishment of a Tsunami Warning Center Page 5

6. Tsunami Warning System - Philosophy • Main Purpose • Issue Warning prior to wave impact on coast • Protect life and property from tsunami hazard by providing tsunami information and warning bulletins to the Area-of-Responsibility • Problem • Wave usually can not be observed prior to impact at near locations • Answer • Issue warning based on associated phenomena (ground shaking and displacement – seismic data) which triggers the wave • Problem • There is not a direct correspondence between the ground shaking and tsunami impact • Reality • Warnings are often issued with no ensuing wave. Page 6

7. Tsunami Warning Systems – What is it? Page 7

8. Tsunami Warning Systems – Basic components • Tsunami Warning Centers • Acquire Data • Process and Analyze • Disseminate Information • Communication Pathways • Robust • Multiple • Tested • Local Emergency Response • Ready to Respond through planning and exercises • Receive Warnings from TWC • Disseminate to local populations • Provide public education Page 8

9. Tsunami Warning Systems – Challenges • Can not monitor phenomena prior to nearest impact • Warning communications to those at highest risk • Hazard definition • Local emergency response • Rare events at any given location • Many threats for which to prepare • Short response time • Poorly educated public Page 9

10. Tsunami Warning Centers • Data acquisition • Seismic • Sea level • Process and Analyze • Initial processing based on seismic data • Decision’s based on processed data and protocols • Post-process seismic data • Analyze sea level data in conjunction with historic and pre-computed models • Disseminate Information • Use all available emergency alert systems • Evacuation decisions made by state/local authorities Page 10

11. Tsunami Warning Centers - Data Acquisition • Seismic • Virtual network • Multiple data paths • Redundancy Page 11

12. Tsunami Warning Centers - Data Acquisition • Sea Level • Virtual network • Satellite data transmission • Many formats • Many instrument types • Coastal tide gages and DART Page 12

13. Tsunami Warning Centers - Data Processing • Seismic • Sea level • GIS – Data bases • Forecasting • Message/graphic generation Page 13

14. Tsunami Warning Centers - Data Processing • Seismic data processing • Initial processing • Location • Depth • Magnitude • Post-processing • Refine Magnitude • Moment tensor (~ 15 minutes) • Mantle magnitude determined Page 14

15. Tsunami Warning Centers - Data Processing • Sea level • Display • Strip-chart view • Detail view • Analysis • De-tide signal • Low pass filter • Measure tsunami Page 15

16. Tsunami Warning Centers - Data Processing • GIS and data bases • Overlay historical data • Compute tsunami travel times • Create web graphics • Interface forecast models Page 16

17. Tsunami Warning Centers - Data Processing • Forecasting • Assimilate observed tsunamis into pre-computed models • Adjust models based on observations • Use forecast to dictate supplemental messages • Observations can also be compared with historical data to forecast impact Page 17

18. Tsunami Warning Centers - Data Processing • Message Generation • Based on source parameters • Text products generated automatically • Conform to NWS and WMO standards • Graphics generated by GIS • Experimental Page 18

19. Tsunami Warning Centers – Disseminate Information • Message Dissemination • Primary • National Warning System • NOAA Weather Wire • NWS gateway • FAA system • Secondary • Email • RSS • FAX • SMS messaging • Web site • USGS Page 19

20. Tsunami Warning Center - Staffing • WC/ATWC • 9 Watchstanders • 1 IT specialist • 2 Electronics technicians • 1 Admin Support • 1 Director • 1 Deputy Director • Center staffed 24x7x2 • Staff activities • Day-to-day operations • Scenario training • Communications testing • Development projects • Outreach Page 20

21. Tsunami Warning System - Summary • Tsunami warning centers and systems historically have been developed in response to devastating tsunamis. • Tsunami warning systems are different from most natural hazard warning systems in that the phenomena itself can not normally be observed prior to impact. • Tsunami Warning Systems consist of: • Tsunami Warning Center • Message Communication Paths • Emergency Response Organizations • Tsunami Warning Centers basic functions are: • Data Acquisition • Data processing and analysis • Message Dissemination Page 21

22. Part 2 – Seismic Data Acquisition • Seismometer • An instrument which records earth vibrations • Converts ground shaking energy into an electrical signal • Extremely sensitive • Output is proportional to ground displacement, velocity or acceleration depending on instrument • Moving coil around magnet generates current • Modern seismometers use electronic force feedback to gain wide spectral response • Signal is normally digitized on site Page 22

23. Similar to our eyes not seeing the entire electromagnetic spectrum in sunlight, seismometers only “see” a portion of earthquake energy. (USGS slide) Page 23

24. EQUIVALENT EARTH PEAK ACCELERATION ( 20 LOG M/SEC 2 ) PERIOD (SECONDS) More than one seismometer is necessary to “see” the entire earthquake energy spectrum (USGS slide) Page 24

25. Seismic Data Acquisition • Seismometer installations • Desired site characteristics: • Low cultural noise levels • Reliable source of power • No vandalism • Ability to “see” communications satellite • Bedrock at or near surface • Long term permitted site • Easy accessibility for maintenance • No overlap with other networks • Data transmission • Private VSAT • Satellite internet • Dedicated circuits • Radio Page 25

26. WC/ATWC Seismometer vault at Middleton I., Alaska Page 26

27. Seismic Waves • Seismology Basics • Three basic types of waves generated by earthquakes • Primary (P) • Secondary (S) • Surface • P waves are sound waves traveling through the earth (the fastest wave) • S waves travel about 60% as fast as P waves • Surface waves area a little slower than S waves • More energy is transmitted in S and Surface waves than P waves Page 27

28. Seismic Waves • Body Waves – travel through the earth • P Waves • Sound Waves • Particle motion in the direction of propagation • S Waves • Particle motion perpendicular to the direction of propagation • Generally caries more energy than the P wave • Surface Waves – travel around earth’s surface • Rayleigh Waves • Elliptical motion in direction of propagation • Size of ellipse related to wave period • Dispersive – peak velocity at about 50s period • Love Waves Page 28

29. Seismic Networks 2004 Sumatra earthquake recorded on several stations of the IRIS Global Seismic Network (USGS slide) Page 29

30. Seismic Networks • Tsunami Warning Centers use available networks to create virtual global networks • Global networks • IRIS Global Seismic Network • CTBTO • National networks • US NSN • Canadian network • Etc. • Regional networks • S. California Seismic Network • Pacific Northwest Seismic Network • Etc. Page 30

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33. IRIS Global Seismic Network Page 33

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36. Seismic Data Transmission • Redundancy is the key • Use redundant path to critical networks • No single path is 100% reliable • Create virtual network out of overlapping regional networks • Reduces dependency on any one network and its server • Utilize two data import computers • Each connects to a network through a separate path Page 36

37. Seismic Data Acquisition at the WC/ATWC Page 37

38. Seismic Network Density for Tsunami Warning Systems • Seismic network variables which influence TWC response time • Station Density • X stations within Ykm from a given location • Station Uptime • Percentage of time station is operating • Data Latency • Length of time it takes for signal to arrive at center • Data quality • Broadband versus short period • These values are the main factors which control a tsunami warning center’s response time • Response time is the length of time it takes after an earthquake origin to issue a message Page 38

39. Seismic Network Density for Tsunami Warning Systems • Seismic Network requirements for a Tsunami Warning Center to issue a message within five minutes • Station Density • 12 evenly distributed stations within 900km of source (2 minute P-wave travel time) • Station Uptime • 80% station uptime • Data Latency • Up to 30s latency • Data quality • Broadband, digital signal Page 39

40. Seismic Network Density for Tsunami Warning Systems • Given the station requirements on the previous slide, a warning timeline response is: • 150s to record signal on 9 to 10 stations • Based on 12 stations within 900 km of epicenter with 80% station uptime and up to 30s latency • 60s to record enough signal after the P to determine magnitude • Using the Mwp moment magnitude technique • 30s extra for analyst review • Need well-trained and experienced analysts • 60s to compose and review appropriate message • Must be automated message generation Page 40

41. Seismic Network Density for Tsunami Warning Systems • Warning Response Timeline can be compressed by: • Increasing station density • Reducing data latency • Reducing station downtime • Decreasing analyst process, review and message generation time • There is a limit to decreasing response times • Large earthquakes have source process times of over 100 seconds • There is an increased danger of false alarms as analyst review time decreases Page 41

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43. Seismic Data Acquisition - Summary • Seismic data are critical to operations at tsunami warning centers • Broadband data provides a more realistic view of earthquake source properties than band limited data • Many networks are available to feed seismic data to tsunami warning centers and the amount of available data is increasing. • Redundancy is important for seismic data feeds so that a TWC is not left blind by the outage of one network • The density, quality, and reliability of seismic data controls a tsunami warning center’s response time Page 43

44. Seismic Data Acquisition: References • USGS Seismology and Tsunami Warnings Training Course – CD - 2006 Page 44