Upper crustal structure of Madeira Island revealed from ambient noise tomography

Matos, Catarina; Silveira, Graça; Matias, L.; Caldeira, Rita; Ribeiro, Maria Luísa; Dias, Nuno; Santos, Telmo Bento dos

doi:10.1016/j.jvolgeores.2015.03.017

Cited by 21 publications

(13 citation statements)

References 34 publications

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“…Generally noise levels in the ocean were on average higher than in the other two environments. However observation conditions are in the deep ocean on average more steady and anthropogene noise sources like ships are (Matos et al 2015;Hannemann et al 2016). The Evora array detected the highest total number of seismic onsets.…”

Section: Monitoring Resultsmentioning

confidence: 99%

“…No historical eruptions are documented on the island, however, the volcanism is classified as active and is divided into three main volcanic stages starting about 5.6 Ma, a main building stage 2.5-1.0 Ma and more recent activity till 6-7 ka (Geldmacher et al 2000(Geldmacher et al , 2005Klügel et al 2009). The upper crustal structure was recently investigated using ambient noise techniques where lower velocities were found in the uppermost layers of the western part of the island and beneath the highest mountains more to the east, the latter embedded in a zone of higher velocities (Matos et al 2015). On the island of Madeira the deployed array consists of 9 broad-band stations of type Guralp CMG 40T (60 s eigenperiod), 3 broad-band stations of type STS2 (120 s eigenperiod) and 12 mid-period sensors of type Lennartz LE-3G (5 s eigenperiod).…”

Section: Data a N D L O C A L S I T E C O N D I T I O N Smentioning

confidence: 99%

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Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array

Dahm

Hannemann

2020

Geophysical Journal International

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SUMMARY A mid-aperture broad-band test array (OBS array DOCTAR) was deployed from June 2011 to April 2012 about 100 km north of the Gloria fault in the Eastern North Atlantic in about 5000 m water depth. In addition arrays were installed on Madeira Island and in western Portugal mainland. For the first time in the Eastern North Atlantic, we recorded a large number of high frequency Po and So waves from local and regional small and moderate earthquakes (ML < 4). An incoherent beamforming method was adapted to scan continuous data for such Po and So arrivals applying a sliding window waveform migration and frequency–wavenumber technique. We identify about 320 Po and 1550 So arrivals and compare the phase onsets with the ISC catalogue (ISC 2015) for the same time span. Up to a distance of 6° to the DOCTAR stations all events listed in the ISC catalogue could be associated to Po and So phases. Arrivals from events in more than 10° distance could be identified only in some cases. Only few Po and/or So arrivals were detected for earthquakes from the European and African continental area, the continental shelf regions and for earthquakes within or northwest of the Azores plateau. Unexpectedly, earthquake clusters are detected within the oceanic plates north and south of the Gloria fault and far from plate boundaries, indicating active intraplate structures. We also observe and locate numerous small magnitude earthquakes on the segment of the Gloria fault directly south of DOCTAR, which likely coincides with the rupture of the 25 November 1941 event. Local small magnitude earthquakes located beneath DOCTAR show hypocentres up to 30 km depth and strike-slip focal mechanisms. A comparison with detections at temporary mid-aperture arrays on Madeira and in western Portugal shows that the deep ocean array performs much better than the island and the continental array regarding the detection threshold for events in the oceanic plates. We conclude that sparsely distributed mid-aperture seismic arrays in the deep ocean could decrease the detection and location threshold for seismicity with ML < 4 in the oceanic plate and might constitute a valuable tool to monitor oceanic plate seismicity.

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Section: Monitoring Resultsmentioning

confidence: 99%

Section: Data a N D L O C A L S I T E C O N D I T I O N Smentioning

confidence: 99%

Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array

Dahm

Hannemann

2020

Geophysical Journal International

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“…For both broad-band and short-period data, waveforms and dispersion measurements tend to stabilize when more than 90 crosscorrelations are stacked (Figs 5a and b), a much lower number than the one used in this work. In order to estimate group velocity uncertainties, we applied a bootstrapping method used by Matos et al (2015). For each interstation path, we have computed the dispersion curves of 10 stacks made with the 75 per cent of all available daily cross-correlations, which have been selected randomly.…”

Section: Quality Controlmentioning

confidence: 99%

Ambient noise tomography of the southern sector of the Cantabrian Mountains, NW Spain

Acevedo

Fernández‐Viejo

Llana‐Fúnez

et al. 2019

Geophysical Journal International

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SUMMARY This study presents the first detailed analysis of ambient noise tomography in an area of the continental upper crust in the Cantabrian Mountains (NW Spain), where a confluence of crustal scale faults occurs at depth. Ambient noise data from two different seismic networks have been analysed. In one side, a 10-short-period station network was set recording continuously for 19 months. A second set of data from 13 broad-band stations was used to extend at depth the models. The phase cross-correlation processing technique was used to compute in total more than 34 000 cross-correlations from 123 station pairs. The empirical Green's functions were obtained by applying the time–frequency, phase-weighted stacking methodology and provided the emergence of Rayleigh waves. After measuring group velocities, Rayleigh-wave group velocity tomographic maps were computed at different periods and then they were inverted in order to calculate S-wave velocities as a function of depth, reaching the first 12 km of the crust. The results show that shallow velocity patterns are dominated by geological features that can be observed at the surface, particularly bedding and/or lithology and fracturing associated with faults. In contrast, velocity patterns below 4 km depth seem to be segmented by large structures, which show a velocity reduction along fault zones. The best example is the visualization in the tomography of the frontal thrust of the Cantabrian Mountains at depth, which places higher velocity Palaeozoic rocks over Cenozoic sediments of the foreland Duero basin. One of the major findings in the tomographic images is the reduction of seismic velocities above the area in the crust where one seismicity cluster is nucleated within the otherwise quiet seismic area of the range. The noise tomography reveals itself as a valuable technique to identify shear zones associated with crustal scale fractures and hence, lower strain areas favourable to seismicity.

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“…In this study, we ignored the effect of topography, as has been done in ANT studies of island volcanoes of similar scale (Mordret et al, 2014;Matos et al, 2015 for La Réunion and Madeira islands, respectively). While Rinjani's maximum height of 3,726 m may seem significant compared to the scale of our study, heights greater than 2000 m are confined to the high relief along the edges of the Salamas caldera, including Rinjani itself.…”

Section: Seismic Data Acquisitionmentioning

confidence: 99%

“…Despite the restrictions on spatial scale imposed by the limited land area, surface wave tomographic surveys have been carried out in volcanic island settings elsewhere of similar scale. In addition to Zulfakriza et al's (2020) survey of the nearby Agung-Batur volcanic complex mentioned above, other studies include the ANT surveys of La Réunion and Madeira islands by Mordret et al (2014) and Matos et al (2015), respectively, the microtremor survey of Jeju Island, Korea by Kim and Hong (2012), and tomographic imaging using earthquake-generated surface waves by Nunziata et al (1999) to study the Campi Flegrei and Somma-Vesuvio volcanic complexes on the island of Sicily, Italy. All of these studies were focussed on resolving shear-wave structure in the upper crust, although Nunziata (2010) also resolved structure as deep as 60 km.…”

Section: Introductionmentioning

confidence: 99%

Delineation of Upper Crustal Structure Beneath the Island of Lombok, Indonesia, Using Ambient Seismic Noise Tomography

et al. 2021

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We have successfully conducted the first ambient noise tomography on the island of Lombok, Indonesia using local waveform data observed at 20 temporary stations. Ambient noise tomography was used to delineate the seismic velocity structure in the upper crust. The waveform data were recorded from August 3rd to September 9th, 2018, using short-period and broadband sensors. There are 185 Rayleigh waves retrieved from cross-correlating the vertical components of the seismograms. We used frequency-time analysis (FTAN) to acquire the interstation group velocity from the dispersion curves. Group velocity was obtained for the period range of 1 s to 6 s. The group velocity maps were generated using the subspace inversion method and Fast Marching Method (FMM) to trace ray-paths of the surface waves through a heterogeneous medium. To extract the shear wave velocity (Vs) from the Rayleigh wave group velocity maps, we utilize the Neighborhood Algorithm (NA) method. The 2-D tomographic maps provide good resolution in the center and eastern parts of Lombok. The tomograms show prominent features with a low shear velocity that appears up to 4 km depth beneath Rinjani Volcano, Northern Lombok, and Eastern Lombok. We suggest these low velocity anomalies are associated with Quaternary volcanic products, including the Holocene pyroclastic deposits of Samalas Volcano (the ancient Rinjani Volcano) which erupted in 1257. The northeast of Rinjani Volcano is characterized by higher Vs, and we suggest this may be due to the presence of igneous intrusive rock at depth.

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Upper crustal structure of Madeira Island revealed from ambient noise tomography

Cited by 21 publications

References 34 publications

Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array

Mapping of Eastern North Atlantic Ocean seismicity from Po/So observations at a mid-aperture seismological broad-band deep sea array

Ambient noise tomography of the southern sector of the Cantabrian Mountains, NW Spain

Delineation of Upper Crustal Structure Beneath the Island of Lombok, Indonesia, Using Ambient Seismic Noise Tomography

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