Using W phase for regional tsunami warning and rapid earthquake hazard assessment Luis Rivera 1 Hiroo Kanamori 2 1 Strasbourg University, Institut de Physique du Globe 2 Seismological Laboratory, Caltech 2nd International Workshop on Earthquake Early Warning Kyoto, April 21-22, DPRI, Kyoto University
W-phase Introduction We have recently developed a source inversion technique based on the waveform modeling of W-phase. W-phase is a very long period (200s-1000s) phase arriving right after the P. It was first recognized after the 1992 Nicaragua earthquake. The inversion technique was originally devised to work for large events (Mw> 7.5) with teleseismic data and it provideas a VLP characterization of the source (e.g. Tsunami earthquakes). We explore here the possibility of an application with regional data and with smaller magnitudes.
W-phase Example: Nicaragua, 1992 Vertical traces - integrated once ANMO, = 28 PAS, = 36 ALE, = 71 1000 s
W-phase Example: Nicaragua, 1992 Vertical traces - integrated once ANMO, = 28 PAS, = 36 ALE, = 71 1000 s
W-phase: Example: Nicaragua, 1992 Deconvolved + bp 200s-1000s Vertical displacement ( µ ) ANMO, = 28 PAS, = 36 ALE, = 71 1000 s
W-phase: Example: Nicaragua, 1992 Deconvolved + bp 200s-1000s Vertical displacement ( µ ) ANMO, = 28 PAS, = 36 ALE, = 71 1000 s
Time window W-phase time-window P, P + 15 s/
W-phase in the global context travel time [s] 2500 2000 1500 1000 500 Global scale P+15 W-phase 0 0 10 20 30 40 50 60 70 80 90 distance [degrees] P S Definition Time window: P, P+15 Bandpass:.001 Hz -.005 Hz Properties Fast group velocity: 4.5-9 km/s Fairly insensitive to: shallow lateral heterogeneities source second order details Avoid large amplitude surface waves
Source retrieval from W-phase Time domain Point source (VLP data) Inversion: main features Need a preliminary source location: PDE, JMA Library of precomputed Green s functions Linear inversion > Moment tensor components PDE ( < 50 ): t 0 + 20 min Grid search ( < 90 ): t 0 + 35 min RT implementation: β-test at NEIC-USGS, (Gavin Hayes)
Example: global data Tokachi-Oki-2003 t 0 + 20 min t 0 + 35 min
Regional data Extension to regional data and lower magnitudes Target: Mw > 6.5 Data distribution: < 12 6 min. > 5 : high gain data, nonlinearity. Modifications: Time window: (P, P+15 ) inappropriate Frequency band: signal/noise ratio
W-phase time window 2500 Global scale 500 Regional scale 2000 400 P+15 12s 6min travel time [s] 1500 1000 P+15 travel time [s] 300 200 500 P 100 P 0 0 10 20 30 40 50 60 70 80 90 distance [degrees] 0 2 4 6 8 10 12 14 16 distance [degrees]
W-phase time window 2500 Global scale 500 Regional scale 2000 400 P+15 12s 6min travel time [s] 1500 1000 P+15 travel time [s] 300 200 500 P 100 P 0 0 10 20 30 40 50 60 70 80 90 distance [degrees] 0 2 4 6 8 10 12 14 16 distance [degrees]
Extension to lower magnitudes Acceleration noise spectrum at MAJO O A B C
Extension to lower magnitudes Acceleration noise spectrum at MAJO O A B C
Extension to lower magnitudes Acceleration noise spectrum at MAJO O A B C
45 130 135 140 145 45 NOP SHR KNP HSS HID URHKSR IMG KMU MMATMR 40 GJM IYG TYS KSN 40 Data: Japanese broadband network (F-net) Events: M jma > 6.7 2003-2008 35 30 YSI YZK NRW IZH YTY NSK TGW ISI OKW SBR INN UMJ TSA FUK STM TKD TMC AMM SIB KYK TKO TAS SAG YAS WJM KZK HRO YMZ ASI SRN ONS TSK KNMTTO SGN TGA NAA FUJ KNY JIZ WTR NOK KIS KMT SBT KZS HJO AOG KSK 35 30 OSW 25 STS 1 STS 2 25 130 135 140 145
F-net, 2003-2008, M jma > 6.7 (1/4)
F-net, 2003-2008, M jma > 6.7 (2/4)
F-net, 2003-2008, M jma > 6.7 (3/4)
F-net, 2003-2008, M jma > 6.7 (4/4)
Regional W phase focal mechanisms (t 0 + 6min) 130 135 140 145 150 112804I 120604A 45 200809110020A 45 200806132343A 092503C 102304D 092503K 200707160113A 40 200703250041A 200807231526A 40 200503200153A 200511142138A 052603A 35 200508160246A 35 090504A 090504D 103103A 200807190239A 30 30 200805071645A 200501190611A 200610232117A 25 STS 1 STS 2 200709281338A 25 20 130 135 140 145 150 20
Regional W-phase, example of fit: 2008 Iwate 200806132343A ( 0.002 Hz - 0.010 Hz, n = 4, W ) 0.094 0.047 KZS KNP TGA NOP YAS NMR WTR NKG SHR ABU HJO YZK KIS NOK SAG AOG KMT ISI NRW YSI UMJ OKW TGW NSK TSA YTY INN SBR TMC IZH TKO STM SIB TAS FUK OSW 0.000-0.047-0.094 mm -0.141-0.188-0.235-0.282-0.329 0 5000 sec
Moment Magnitude: gcmt - W-phase 8.5 +0.1-0.1 8.0 W phase Mw 7.5 7.0 6.5 6.0 6.0 6.5 7.0 7.5 8.0 8.5 gcmt Mw
2003 Tokachi-oki: depth effect H = 45km δ = 29 M w = 8.02 H = 28km δ = 14 M w = 8.15 HVD(H = 28km) δ = 11 M w = 8.26
Conclusions We use F-net data in the range (5 < < 12 ) Time window: t P, t P + 180s Variable frequency band: (.00167Hz.005Hz) (.005Hz.010Hz) Moment tensor solution available at t 0 + 6min Can be done completely automatic and Provide a solution 6 min after the origin time.