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Abstract. The Canary Islands volcanic complex is studied in terms of coda wave attenuation. A multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers, is applied to

The tectonic plate boundary between Eurasia and Africa is complex, in that it cannot be characterized as a single discrete plate boundary Deformation near this plate boundary varies from trans‐tensional in the Azores archipelago, through strike‐slip in the eastern Atlantic basin, to overall compressional between the European and African continents, with extensional sub‐domains in the Mediterranean Sea. This complex pattern of deformation, related plate motion, and underlying driving forces leads to strong variations in seismic hazard throughout the region. A better understanding of the plate boundary processes requires knowing crust and upper mantle structure in the region, which is best investigated with three‐component, broadband seismic data. To investigate the region's three‐dimensional crust and upper mantle structure, we are carrying out a multiinstitutional project (MIDSEA) involving seismologists from 10 countries on the northern, southern, and western sides of the plate boundary.

S U M M A R YThe anelastic attenuation in the Almeria Basin (southeastern Iberian Peninsula) is investigated by using seismic data collected during the summer of 1991. A multiple-lapse time-window analysis is applied to high-frequency seismograms corresponding to 20 shallow seismic events with low magnitudes ( m 12.5) and distances less than 71 km, recorded at six short-period seismographic stations. We have constructed corrected geometrical spreading and normalized energy-distance curves for the region over the frequency bands 1-2,2-4,4-8,8-14 and 14-20 Hz. A theoretical model for body-wave energy propagation in a randomly heterogeneous medium has been employed to interpret the observations. Two parameters describe the medium in this model: the scattering attenuation coefficient qs = kQ3 ' and the intrinsic attenuation coefficient yI = kQ, ', where k is the wavenumber and Qr1 and Q, are the intrinsic and scattering attenuation respectively. This model assumes that scattering is isotropic, including all orders of multiple scattering, and predicting the spatial and temporal energy distribution of seismic energy. A least-squares fitting procedure has been used to find the best estimates of the model parameters. The analysis of the spectral amplitude decay of coda waves has provided coda Q,' values at the same frequency bands. The results obtained show that Q, ', Q2 ' and Q, ' decrease with increasing frequency; for frequencies lower than 3 Hz scattering attenuation is stronger than intrinsic absorption and coda Q, ' takes values between intrinsic and total attenuation, being very close to Qy'. Q;' is more frequency-dependent than Q, ; for frequencies greater than 3 Hz intrinsic absorption is the dominant attenuation effect and Q, and Q3 have significant frequency dependence. In order to correlate the results obtained with the major geological and tectonic features of the region, a geotectonic framework for the area is provided and the predominant frequency decay in coda waves is analysed in order to obtain the coda Q frequency dependence following a power law Qc = Qo( f/fo)", where fo is a reference frequency. In this way we have obtained regionalized values of coda Q at 1 Hz (Qo). Finally, a first-order approach has allowed us to obtain intrinsic and scattering quality factors from the obtained QO and v values, leading us to obtain tentative distributions of Q,, Qs and QO at 1 Hz for the area. The derived intrinsic and scattering quality-factor distributions are in good agreement with the tectonic history and the main geological features of the region. Large scattering and intrinsic attenuation (Qs N 80, QI -100) are found in the sedimentary Neogene and Quaternary basin, while scattering is the dominant effect in the old Palaeozoic rocks of the mountains (Qs -200, QI -1000).Intrinsic Q shows a higher sensitivity to the geological characteristics than scattering Q.

In this study, we investigate 70 days of distributed acoustic sensing (DAS) recordings in the Canary Islands using an undersea fiber-optic telecommunication cable that links the islands of Tenerife and Gran Canaria. Two DAS interrogators connected to both ends of the cable turned the fiber into an array of 11,968 strain sensors covering a total length of ∼120 km. We present the details of the experiment, noise analysis, and examples of recorded signals. Seismic ambient noise levels assessment indicates poor local coupling of the cable due to the irregular bathymetry that results in high-amplitude acoustic oscillations in some channels. The DAS array recorded several types of nonseismic (vehicles, surface gravity waves, ships) and seismic signals. Local and regional earthquakes were detected with magnitudes mbLg≥2. Surface waves from teleseismic events at a distance of ∼3000 km were also identified in the strain recordings. Here, we report the first observations with DAS of hydroacoustic T waves generated by oceanic earthquakes located at the Central Mid-Atlantic Ridge and the Cape St. Vincent region. Events had magnitudes from Mw 4.2 to 6.9, and the hydroacoustic waves were recorded at epicentral distances from 780 to 3400 km. Our findings show that submarine fiber-optic cables can effectively be used to assess the seismic activity in remote oceanic areas.