Seismic Background Noise Characterization at the Magdalena Ridge Observatory Interferometer Site

Details Seismic Background Noise Characterization at the Magdalena Ridge Observatory Interferometer Site Seismic Background Noise Characterization at the Magdalena Ridge Observatory Interferometer Site

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.s52d0164a&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #S52D-0164

Astronomy and Astrophysics

Astronomy

7299 General Or Miscellaneous, 7594 Instruments And Techniques

Scientific paper

We performed a seismic site characterization in central New Mexico for the ˜350-m baseline Magdalena Ridge Observatory (MRO) astronomical interferometer, which will operate at wavelengths between 600 nm and 2400 nm. The operation of an interferometer requires that optical path lengths be stable to within considerably less than one wavelength over the measurement timescale. The study analyzed 1-hour absolute and differential background noise windows at element locations between February and October of 2003. Data were acquired with IRIS PASSCAL stations consisting of four 3-component broadband 120-s STS-2 sensors in shallow vaults and Quanterra Q330 digitizers with both real-time 802.11 telemetry and on-site Baler14 recorders. Sensors were deployed at the ends of each of the three interferometer arms, and at the center of the array. The analysis focused on seismic noise during local night-time hours. Night-time noise levels at the site typically reside in the lower half of the Peterson (1993) Global Seismic Network noise model. With the exception of noise inside the microseismic band ( ˜0.1 to 0.7 Hz), background noise is generally incoherent at both longer and shorter periods. Differential noise in the short-period band (< 1 s) is of particular interest, as it poses the greatest challenges for active optical systems. In general, differential displacements are well below 25 nm, even during periods of high wind. Noise produced by a 150-kW generator run by a V12 Detroit Diesel engine, about 0.6 km from the site, produced maximum RMS absolute and differential displacements of approximately 6 nm and 7 nm, respectively. In comparison, noise spikes produced by medium-sized trucks passing near the site typically result in maximum RMS absolute and differential displacements of about 60 nm and 80 nm, respectively. We conclude that teleseisms (e.g., the Algiers earthquake of 2003 May 21, Mw 6.7) and local earthquakes (Md > 1) from the Socorro seismic region are the only naturally-occurring events likely to produce differential displacements larger than 25 nm and thus capable of inducing loss of interferometer coherence. We will further assess the general issue of whether seismic noise is likely to present difficulties for optical or infrared interferometers at sites with noise characteristics lying between the Peterson high and low noise curves.

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