Faster Earthquake Early Warning Using Superconducting Gravity Gradiometers

Transcription

1 Faster Earthquake Earl Warning Using Superconducting Gravit Gradiometers Ho Jung Paik Universit of Marland NIMS, Ma 5, 07

2 What is Earthquake Earl Warning? abilit to provide a few to tens of seconds of warning before damaging seismic waves arrive seismogram P-wave fast not damaging Paik S-wave slow damaging

3 Paik 3

4 How can we use EEW?. Public Alert Warn people to take protective measures (drop-cover-hold on) Move people to safe positions Prepare phsicall and pschologicall for the impending shaking. Trigger Automatic Responses Slow down/stop trains Control traffic b turning signals red on bridges, freewa entrances Close valves and pipelines Stop elevators Save vital computer information Limitations: Chance of false/wrong alerts: need to account for finite rupture size No warning in blind zone (~30 km around epicenter) Paik 4

5 Blind zones of EEWS US West Coast earthquake hazard Blind zone size in California (Kuuk and Allen, 03) To reduce the blind zone, can we use gravit signals that travel at c, 0 5 times faster than seismic waves? Paik 5

6 Gravit signals from Tohoku earthquake GRACE and GOCE missions have measured static gravit changes after vs before large earthquakes. Can dnamic gravit signals following fault rupture be measured quickl? Paik 6

7 Static GG signals from Tohoku earthquake h h h zz h h z h z Courtes of J. Harms Paik 7

8 Dnamic gravit changes induced b earthquakes: Theor The perturbation of the gravit potential is Distance Radiation pattern Double integral of seismic moment Gravit strain acceleration: From presentation b P. Ampuero (Caltech Seismolab) Paik 8

9 Comparison to numerical simulation: Verification We implemented finite kinematic sources and computation of gravit field in the 3D spectral element program SPECFEM3D. The signal decas as /r 5, as predicted, even for dipping faults Paik 9

10 Epected dnamic gravit signal Ampuero et al., Prompt detection of fault rupture for earthquake earl warning (preprint) Gravit signal following a rupture SNR after 5 s Epicentral distance = 70 km Net stage: h = 0 5 Hz /, MANGO: h = 0 0 Hz / SNR after 0 s Paik 0

11 Gravit gradients To measure gravit, field on two or more masses must be differenced. Gravit gradient ij is a smmetric 3 3 tensor: ij i j independent components 0 ii : inline-component ij (j i): cross-component Paik

12 Superconducting accelerometer Low noise: S a ( f ) kbt EA( f ) m Q Stable scale factors Sensitive differential measurement possible. Paik

13 Superconducting Gravit Gradiometer (SGG) I I L m L L m L a Low noise: S ( f ) kbt E ( f ) A m Q I /I are adjusted to balance out CM. Stable CM rejection > 0 7. S / ( f ) 0 3 E Hz /,E 0-9 s ( zz,earth 30 3 E) Paik 3

14 Model SGG Sensitive SGGs have been under development for over 30 ears at UM. L B I B TEST MASS L L L t L S L t R SP I S - I S I S R SS I L L S3 SQUID I S R L L S TEST MASS R BS L L I B L B R BP Mood et al., RSI 73, 3957 (00) Test masses are mechanicall suspended (f DM ~ 0 Hz). CM platform vibration noise is rejected to 3 parts in 0 8. Paik 4

15 Performance of Model SGG Gravit gradient noise PSD 0 - Hz -/ 0-5 m Hz -/ B earl 990 s, SGG achieved sensitivit 0 3 times better than atom interferometers to date. Paik 5

16 Demonstration of Model SGG Paik 6

17 Tensor SGG with levitated test masses More sensitive SGG is under development with NASA support. Test masses are magneticall suspend (f DM ~ 0.0 Hz) times higher sensitivit Test masses are levitated b a current induced along a tube. Si test masses mounted a cube form a tensor gradiometer. Paik 7

18 Earth science SGG mission Tensor SGG with sensitivit E Hz / over 0.5 ~ 50 mhz. SGG could be tuned during the mission to ield higher sensitivit at low frequencies where time-variable gravit signals are. Crocooler will permit 0 ear mission lifetime. Instrument noise spectral densit Paik 8

19 SOGRO (Superconducting Omni-directional Gravitational Radiation Observator) Each test mass has 3 DOF. Combining si test masses, tensor GW detector is formed. h h ii ij t t t L t t, i j t t t L ii ij ii ij ji Source direction (, ) and wave polarization (h+, h) can be determined b a single antenna. Spherical Antenna ji + polarization polarization Paik 9

20 SOGRO would fill 0.-0 Hz frequenc gap between the terrestrial and future space interferometers. Astrophsics with SOGRO asogro would be able to detect stellar mass BH binaries like GW5094 and alert interferometers das before merger. SOGRO could detect IMBH binaries with M at a few billion light ears awa, and WD binaries within the Local Group. Paik 0

21 Paik Magnetic levitation To provide large area for levitation, test mass is made in the shape of square Nb shell with flanges. Horizontal DM frequencies can all be tuned to 0.0 Hz. However, due to nonlinearities, strong levitation fields will cause vertical DM frequencies > Hz. Vertical accelerometers will be noisier. Since the platform is isolated from tilt of the ground, h z and h z can also be obtained from horizontal motions of test masses onl., z z z z z z zz z z L h z z L h L h h h h L h L h z z z z L L

22 SEED (Superconducting Earthquake Earl Detector) S ( f ) kbt E ( f ) A m Q B levitating two Nb test masses (M = 0 kg, L = 50 cm) separated along z ais, h 3 and h 3 are measured. Test masses are cooled to.5 K and coupled to 0 SQUIDs via a capacitor bridge transducer. To reject the seismic noise to below the intrinsic noise, CMRR = 0 9 is achieved. at 70 km QD SQUID 0 SQUID Paik

23 SEED design overview Paik 3

24 Detection range of SEED and SOGRO SEED has a range of 50 km for M6 earthquake. SOGRO has a range of 350 km for M6 earthquake. Paik 4

25 Collaborative development of SEED A joint proposal is being prepared in US. UM Caltech JPL (Paik) SEED instrument development (Shawhan) Earthquake gravit signal etraction (Ampuero) Earthquake gravit signal modeling (Crogenics group) Advanced SQUIDs International collaboration is under development. Korea China Ital SOGRO collaboration KIGAM? CAS Technical Institute of Phsics and Chemistr Jan Harms group (INFN) Paik 5