ABSTRACT

A low-frequency passive seismic experiment using an array of 49 3C broadband seismometers was conducted over an onshore oil field in the emirate of Abu Dhabi in the United Arab Emirates. The aim of the experiment was to understand the characteristics and origins of the microseism (0.15–0.4 Hz) and microtremor (about 1–6 Hz) signals recorded, the latter having been reported as being a hydrocarbon indicator above several reservoirs in the region. The recorded array data were analyzed for their polarization, apparent velocities, and wavefront azimuths using various techniques, including spectral and time-frequency analyses, particle motion, H/V spectral ratios, and high-resolution frequency-wavenumber (f-k) analyses. In the frequency range of 0.15–0.4 Hz, the dominant feature observed consisted of double-frequency microseisms peaks generated by the nonlinear interactions of ocean waves with the shoreline along the coasts of the Arabian Sea and the Arabian Gulf. The f-k analyses confirmed that microtremor events in the frequency range of 2–3 Hz have an azimuth pointing toward a major oil pipeline and oil plant facilities to the west–southwest of the study area, as well as a motorway to the southeast. This would indicate that the microtremor events are probably caused by local sources, including the continuous movement of oil through the pipeline, the noise from oil plant facilities, as well as nearby traffic noise. This interpretation was confirmed by the polarization analysis performed on the data. The data also indicated that no clear correlation exists between the microtremor signal and local meteorological conditions. Although some body waves with an infinite apparent velocity generated by earthquakes were recorded, no other body waves that could have possibly been generated by hydrocarbon reservoirs were observed using the analyses techniques used in this study. Therefore, our results indicated that for the site under investigation, the microseism and the microtremor signals detected could not be related to the presence of hydrocarbon accumulations in the subsurface, but instead they may be attributed to local anthropogenic sources.

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