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U. Washington Tsunami Certificate Program Course 2: Tsunami Warning Systems Session 7 Tsunami Warning Data Processing July 28, 2007 1:15-2:45pm. Outline. Seismic Data Processing Seismic Basics Seismic Processing Architecture Sea Level Processing GIS Data bases Forecasting Techniques

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  1. U. Washington Tsunami Certificate ProgramCourse 2:Tsunami Warning SystemsSession 7Tsunami Warning Data ProcessingJuly 28, 2007 1:15-2:45pm Page 1

  2. Outline • Seismic Data Processing • Seismic Basics • Seismic Processing Architecture • Sea Level Processing • GIS • Data bases • Forecasting • Techniques • Exercise Page 2

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  4. Earth Cross-section Page 4

  5. Seismic Basics – Earthquake Rupture • Earthquake Strain Build-up and Rupture similar to bending a plastic ruler • Build-up of Stress (strain energy) • Can’t predict where or when ruler will break • Breaks at weakest point • May hear precursors • Sound of breaking same as seismic waves Page 5

  6. Seismic Basics – Earthquake Rupture • Elastic Rebound Theory • Henry Reid – 1910 • Based on studies of 1906 San Francisco earthquake • Strain Builds up • When strain exceeds fault strength, fault slips • Elastic energy released at time of slippage Page 6

  7. Seismic Basics – Earthquake Rupture • 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 7

  8. Seismic Basics – Earthquake Rupture • Three basic types of earthquake rupture • Reverse Fault • Hanging wall moves up relative to footwall • Common in compressive environments like subduction zones • Thrust faulting is a special type of reverse fault • Shallow dip angle • Most major earthquake-generated tsunamis are triggered by this type of faulting Page 8

  9. Seismic Basics – Earthquake Rupture • Three basic types of earthquake rupture • Normal Fault • Hanging wall moves down relative to footwall • Common in extensional environments like basin and range provinces (and within subducting plates) • Many earthquake-generated tsunamis are triggered by this type of faulting Page 9

  10. Seismic Basics – Earthquake Rupture • Three basic types of earthquake rupture • Strike-slip Fault • Fault motion is horizontal • Faults are normally high angle to surface • Common in mid-ocean ridges and transform plate boundaries • Not as likely to trigger tsunamis as dip slip quakes, but many large local tsunamis have been triggered by this type of quake • Right lateral v. left lateral Page 10

  11. Seismic Basics – Earthquake Rupture • Parameters which define earthquake rupture • Strike • Dip • Slip • Length • Width • Depth • Moment • Rupture Velocity • Slip Velocity • Rock Properties Page 11

  12. Seismic Basics – Earthquake Location • Four unknowns • Origin Time • X/Y/Z • Solve using phase arrival times • Needs good velocity model of earth • S Minus P time approach • S-P time increases with epicentral distance • Each station which records S and P waves provides a distance from station to epicenter • Three stations with S-P needed for location Page 12

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  14. Seismic Basics – Earthquake Location • P-wave only method • The location has 4 unknowns (t,x,y,z) so with 4+ P arrivals this can be solved. • The P arrival time has a non-linear relationship to the location, even in the simplest case when we assume constant velocity – therefore can only be solved numerically • Use a Least squares method – minimize residuals between observed and calculated travel times Page 14

  15. Seismic Basics – Earthquake Location • Automatic Locations • Seismic data analyzed by routine which determines onset of P wave • P-time sent to associating/locating algorithm • Associator attempts to split P-times into buffers which contain P-picks from same earthquake • When 5 picks accumulate in a buffer, quake will automatically locate. Page 15

  16. Seismic Basics – Earthquake Magnitude • Magnitude • 1935 Charles Richter related amplitude on a seismometer to energy release and created a “magnitude” scale • Many scales used, though most use the same energy/magnitude relationships as devised by Richter • Each magnitude scale is appropriate for a certain type or size event. • All magnitude scales are logarithmic • 1 unit on scale equates to 10x the ground motion • 1 unit equates to approximately 32x energy release • Tsunami Warning Systems are concerned mainly with fast evaluation of large earthquakes • Four different types of magnitudes computed at WCATWC Page 16

  17. Seismic Basics – Earthquake Magnitude • Body wave and Local Magnitude (mb and Ml) • Evaluated after automatic or interactive P-pick • Determined very quickly after event • Determined on short period filtered data (0.3 – 3s period) • Max amplitude (and corresponding frequency) in first 15 cycles of waveform is used to determine mb once location is known • Max amplitude (and corresponding frequency) beyond 15 cycles and less than 2.5 minutes is used to determine Ml once location is known • Based on epicentral distance, mb or Ml is computed • mb > 15 degrees • Ml < 9 degrees • Ml generally accurate in the range 0-6.75 for shallow quakes • Mb generally accurate in the range 4.5-6.5 for any depth quakes Page 17

  18. Seismic Basics – Earthquake Magnitude • Surface Wave Magnitude (Ms) • Evaluated cycle by cycle on surface waves after location determined • Takes longer to compute than mb/Ml • Determined on long period filtered data • Automatically computed for all quakes over magnitude 5 • Based on location, Rayleigh wave start time determined • Signal evaluated for one minute before R-wave to 30 minutes after • Period range 18-22 seconds used • Epicentral distance must be at least 5 degrees • Accurate for shallow quakes in the general range 5.5 – 7.75 • Ms/mb good discriminator for deep quakes Page 18

  19. Seismic Basics – Earthquake Magnitude • Moment Magnitude based on integrated P waveform (Mwp) • Evaluated 50s, 100s, 150s, and 200s after P-pick • Developed in 1990s by Tsuboi - ERI • Determined on broadband data • Signal-to-noise ration checked, must exceed threshold value • The longer the frequency response of instrument, the better the result • Velocity signal integrated twice • Time of integration dependent on corner frequency of signal • Mwp based on integrated displacement signal amplitude • Accurate for quakes in the general range 5.5 – 8.0 • Fastest way to determine moment magnitude Page 19

  20. Seismic Basics – Earthquake Magnitude • Moment Magnitude based on mantle waves (Mm) • Evaluated after 11 minutes of Rayleigh wave signal is recorded • Epicentral distance must be greater than 16 degrees • Developed in 1990s by French Polynesia TWS group • Determined on response-corrected, broadband data • Spectra computed for 11 minutes of Rayleigh wave data • Maximum spectral amplitude chosen • Magnitude computed based on amplitude and rock properties over source/receiver path • Accurate for quakes in the general range 6.25 – 8.75 • Most accurate TWS method to determine moment magnitude for really big quakes Page 20

  21. Seismic Basics – Earthquake Magnitude • Inversion techniques • USGS techniques • Compare observed seismogram to a synthetic signal • Produces • Moment magnitude • Depth • Strike • Dip • Slip • Moment Tensor • 12-20 after O-time to compute Page 21

  22. Seismic Processing Architecture • USGS Earthworm Architecture • Developed as tool for regional networks • Used as basis for U.S. Tsunami Warning System to exchange seismic data • Earthworm Philosophy • Modular Approach • Each module performs one function • Modules attach to rings (shared memory) • Modules communicate by sending messages via the rings Page 22

  23. Seismic Data Acquisition at the WC/ATWC Page 23

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  25. Seismic Data Processing • WCATWC Earlybird System • Developed for fast processing of Big earthquakes • GUIs to refine automatic results • Redundant backup operates concurrently Page 25

  26. Seismic Data Processing (1) • Real-time processing • Seismic alarms are triggered based on strong signal at one or more stations • All data processed at 20-25 sps to determine onset of P wave • Automatic locator sorts P-arrivals into buffers for different events • Locations computed when buffers fill up with 5 P-picks • Time to first auto-location depends on station density • High density -> < 1 minute • Low density -> 5-10 minutes Page 26

  27. Seismic Data Processing (2) • Geophysicist refines automatic location • Earthquake depth estimations made both automatically and interactively • Initial locations accompanied by Ml/mb magnitudes • Mwp compute approximately 60s later • Initial analysis complete Page 27

  28. Seismic Data Processing (3) • After initial message disseminated, processing continues: • Refine Mwp (5-15 minutes) • Compute moment tensor (12-20 minutes) • Compute Mm (20-60 minutes) Page 28

  29. Sea Level Processing • Geophysicist refines automatic location • Earthquake depth estimations made both automatically and interactively • Initial locations accompanied by Ml/mb magnitudes • Mwp compute approximately 60s later • Initial analysis complete Page 29

  30. Sea Level Processing • Data written to disk in common format • Display programs retrieve disk data • Display in detailed or strip chart view • Data de-tided • Low pass filtered • Interactively measure amplitude/period • PTWC Tide Tool • Contact Stu Weinstein at PTWC Page 30

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  32. Sea Level Data Format • Adak,_AK 9461380 NOS Continuous 51.863 -176.632 20070514 • NGWLMS m UTC 1 min MLLW WCATWC Unfiltered • 1_minute_NOS_data_via_GOES • Data Format: SampleTime(epochal 1/1/1970) WaterLevel SampleTime(yyymmddhhmmss) • 1179100800 1.288000 20070514000000 • 1179100859 1.288000 20070514000059 • 1179100919 1.290000 20070514000159 • 1179100979 1.291000 20070514000259 • 1179101039 1.294000 20070514000359 Page 32

  33. Geographical Information Systems • GIS uses in a TWC • Provides the analyst good situational awareness • Relates source zone to tectonic environment • Relates source zone to cultural and population centers • Interactive access to historical tsunami and earthquake data bases • Compute and display tsunami travel time maps • Interface with forecast models • Many types of cultural and geophysical overlays • Produce graphics for distribution to web sites. Page 33

  34. Geographical Information Systems • EarthVu GIS developed at WCATWC • Uses the Geodessey Ltd Hipparchus software as a base • Written in C for Windows environments • Can be re-programmed to provide outputs desired by analysts Page 34

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  37. Historical Data Bases • Access to accurate historical tsunami and earthquake data bases is critical for TWCs • Tsunami data bases provide a method to determine what size events can produce damage • Provide data which can be used during an event to estimate effects elsewhere • Prior to events, historic tsunami information can be used to help set response procedures • Used to determine an area’s overall hazard • Detailed historic information can be used to estimate inundation limits in some cases Page 37

  38. Historical Data Bases • Data Sources (for example) • NOAA/National Geophysical Data Center • http://www.ngdc.noaa.gov/seg/hazard/tsu.shtml • Russian Academy of Sciences • http://tsun.sscc.ru/tsun_hp.htm • Tsunami Bulletin Board • International Tsunami Information Center Reports • National historic tsunami studies Page 38

  39. Historical Data Bases • Example of WCATWC data base retrieval and GIS Page 39

  40. Historical Data Bases Page 40

  41. Historical Data Bases Page 41

  42. Tsunami Forecasting • Purpose • To predict amplitudes at coast and drive proper emergency response • Basics • Assimilate observations into numeric models • Some techniques just use pre-computed models based on earthquake parameters without adjustment with sea level observations • Full-ocean tsunami models compute slower than waves propagate when detailed resolution is used • At least some part of the models must be pre-computed • Techniques used at U.S. TWCs • SIFT – Session 6 • TWC technique – More here • JMA approach • All pre-computed • No adjustment based on observations Page 42

  43. Tsunami Forecasting • TWC method • Based on Zygmunt Kowalik (U Alaska) technique • Long wave equations • Coriolis • Bottom Friction • Non=linear terms • Finite Difference Approach • Space staggered grid • No inundation • Dynamic grid interactions • 5’ increment in deep water • 1’ increment on shelf • 12” increment near shore • Source – static vertical motion based on earthquake parameters Page 43

  44. Tsunami Forecasting • TWC application • Determine likely fault parameters for Pacific subduction zone quakes • Model quakes of different magnitude in each zone (several hundred) • Save maximum amplitudes throughout model • During Event: • Based on quake’s location and Mw, choose most appropriate model • Scale previously computed amplitudes based on recorded amplitudes outside source zone • Scaling averaged as more amplitudes recorded • Make decision on warning expansion or restriction based on predicted amplitudes • Test on all large Previous events Page 44

  45. Tsunami Forecasting Page 45

  46. Tsunami Forecasting • Pitfalls • Source region difficult to forecast • Time constraint • Secondary sources • Later waves hard to forecast • Model assumptions • 2d • Resolution • Source uplift Page 46

  47. Tsunami Warning Data Processing - Summary • The most important aspects of seismology to the tsunami warning system are how earthquakes trigger tsunamis and how earthquakes are rapidly characterized after an event. • Earthquake magnitude determination sometimes seems more like an art than science. • TWCs must be able to quickly process and review events. The processing software must be optimized for large events. • A GIS which interacts with the rest of the processes is critical at a TWC. • Tsunami data bases provide important information for use both before and during an event. • Tsunami forecasts are used to guide supplemental decisions during events. Page 47

  48. Tsunami Warning Data Processing: References • USGS Seismology and Tsunami Warnings Training Course – CD - 2006 Page 48

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