capturing the “hum” of the earth on low frequency seismic arrays
DESCRIPTION
Capturing the “hum” of the Earth on low frequency seismic arrays. Barbara Romanowicz Univ of California, Berkeley in collaboration with: Junkee Rhie. 0S8. 0S4. 0S5. 3S2. 0S9. 0S10. 0S11. 0S13. 2.2. 0.6. mHz. Quiet Days Station SUR. 0S22. 0S65. Kobayashi and Nishida, 1998. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/1.jpg)
Capturing the “hum” of the Earth on low frequency seismic arrays
Barbara Romanowicz
Univ of California, Berkeley
in collaboration with: Junkee Rhie
![Page 2: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/2.jpg)
![Page 3: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/3.jpg)
0S80S4 0S100S9 0S130S113S20S5
0.6 2.2mHz
![Page 4: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/4.jpg)
Kobayashi and Nishida, 1998
0S22 0S65Quiet Days Station SUR
![Page 5: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/5.jpg)
![Page 6: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/6.jpg)
Tanimoto, 2000437 quiet days over 10 years
![Page 7: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/7.jpg)
Tanimoto, 2000
Observed
Syntheticwith realdistrib. ofM<5.8
![Page 8: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/8.jpg)
Ekström, 2000
Phase shifted 15 days with respect to winter solstice
![Page 9: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/9.jpg)
Location of “hum” using an arraymethod
• Two main broadband seismic arrays equipped with STS-1 seismometers:– BDSN, California– F-NET, Japan
• 3rd array: GRSN (STS-2)
• Data filtered in the band 150-400 sec, or use of Gaussian filter centered at 240 sec.
![Page 10: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/10.jpg)
BDSN array
![Page 11: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/11.jpg)
Stack Amplitude as a function of time and azimuth, FNET
Jan, 2, 2000Mw 5.7 = 74.17o
Verify sizeof eq
![Page 12: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/12.jpg)
Quiet Day: 2000.031
FNET BDSN
![Page 13: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/13.jpg)
January 31, 2000
FNET+BDSN+Europe
![Page 14: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/14.jpg)
BDSN FNET
Red = winter average(oct-march)Blue = summer average (april-sept)Black = yearly average
Year 2000
2 x 10-10 m/s 0.5 ngal
![Page 15: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/15.jpg)
Winter 2000
Summer 2000
![Page 16: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/16.jpg)
Significant wave height (Topex-Poseidon)
Seismic background noise
Rhie and Romanowicz, 2004
![Page 17: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/17.jpg)
Excitation mechanism
• Involves coupling between atmosphere/ocean and solid earth– energy dissipation in the oceans
• Further understanding:– need for STS-1 or equivalent large aperture arrays,
especially in the southern hemisphere (e.g. Australia)
– arrays in the ocean spanning the entire water column
![Page 18: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/18.jpg)
![Page 19: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/19.jpg)
Degree 1 term in azimuth
![Page 20: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/20.jpg)
FNET BDSN
Red: winterBlue: summer
black: array response
Spectra
![Page 21: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/21.jpg)
SummerWinter Winter
Year 2000
Red = BDSN; back-azimuths = 295o (winter); 105o (summer)
Blue = FNET; back-azimuths = 65o (winter); 235o (summer)
Correl. Coef. =0.78
![Page 22: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/22.jpg)
“Quiet day”:01/31/2000
![Page 23: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/23.jpg)
Day 200l.031 54500-55500 sec
![Page 24: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/24.jpg)
FNET
BDSN
Jan 31,2000
BDSN
![Page 25: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/25.jpg)
Jan 2, 2000Mw 5.8 = 36.31o
![Page 26: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/26.jpg)
Year 2001
![Page 27: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/27.jpg)
![Page 28: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/28.jpg)
![Page 29: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/29.jpg)
![Page 30: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/30.jpg)
![Page 31: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/31.jpg)
Excitation mechanism
• Must involve coupling between atmosphere, ocean and solid earth:– Wind generated waves (~10-20sec)– Conversion to long period infragravity waves (100-
300 sec) by non-linear interactions near the shore– bounded and free infragravity waves
– Coupling of infragravity waves to solid earth in the deep ocean
– depends on ocean basin width, depth and shape of coasts
![Page 32: Capturing the “hum” of the Earth on low frequency seismic arrays](https://reader036.vdocuments.site/reader036/viewer/2022062408/568143f6550346895db080cd/html5/thumbnails/32.jpg)
• Very few “point source” like events found:– “Slow earthquakes” (e.g. Beroza and Jordan, 1990)
detectable in the period band 150-400 sec are very rare, in contrast to the shorter period band 30-150 sec (e.g. Ekström et al., 2003).
• Further analysis:– Distributed sources
• random around the globe?