1 / 48

Outline

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

clamoureux
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

  3. Page 3

  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

  13. Page 13

  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

  24. Page 24

  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

  31. Page 31

  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

  35. Page 35

  36. Page 36

  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

More Related