Real Time Data from US East Coast
Nelson-Nordgren, Astatic Spring, Broadband Force Balance, Vertical (FBV) Seismometers

Using the magnitude squared coherence function, gamma2, to help dig out Spherical Earth modes



These Spherical Earth Modes were observed from two broad band Yuma seismometers, in the basement of a residential home in Princeton Junction, NJ. The high gain output, 28,300 V/m/s, was used with a period extending inverse filter, in WinSDR, which increases the response down to approximately 0.002Hz. The signals used were from the M8.2 Chilean earthquake of 4/1/2014, starting at 4/2/2014 05:00:00 UTC and continuing for 91 hours. The Fourier spectrum of each signal was point-by-point averaged, de-trended, and scaled to produce a single spectrum. This spectrum was then compared to gamma2 in three frequency bands: 2.0mHz-3.5mHz, 3.5mHz-5.0mHz, and 5.0mHz- 6.0mHz. The following graphs for each band show the overlay of coherence and Fourier spectrum and the points singled out for frequency measurement. The interpretation is somewhat seat-of-the-pants at times, but the values seem to agree with published results. The frequency values and digits of precision are reported by Sigview and there was no attempt to put error bars on the results.

----Measured Modes----

Mode mHz
0S12 ----- 2.0203
0S13 ----- 2.0935
? ---------- 2.1759
0S14 ----- 2.2888
0S15 ----- 2.359
0S16 ----- 2.42
? ---------- 2.4963
0S17 ----- 2.5818
0S18 ----- 2.6703
0S19 ----- 2.774
0S20 ----- 2.8748
0S21 ----- 2.9785
0S22 ----- 3.0975
0S23 ----- 3.1769
0S24 ----- 3.2684
0S25 ----- 3.36
0S26 ----- 3.4546
0S27 ----- 3.5492
0S28 ----- 3.6285
0S29 ----- 3.7415
0S30 ----- 3.8147
0S31 ----- 3.9063
0S32 ----- 3.9825
0S33 ----- 4.0833
0S34 ----- 4.1656
------------ ------
0S40 ----- 4.715
0S41 ----- 4.7852
0S42 ----- 4.8889
0S43 ----- 4.9927
0S44 ----- 5.0964
0S45 ----- 5.1636
0S46 ----- 5.2704
0S47 ----- 5.3223
0S48 ----- 5.4169
0S49 ----- 5.481
? ---------- 5.5389
0S50 ----- 5.6091
0S51 ----- 5.7007
0S52 ----- 5.7831
0S53 ----- 5.8899



Coherence and Spectrum plots for 2.0mHz-3.5mHz.



Coherence and Spectrum plots for 3.5mHz-5.0mHz.



Coherence and Spectrum plots for 5.0mHz-6.0mHz.