Multi-array analysis of volcano-seismic signals at Fogo and Brava, Cape Verde
<p>Seismic arrays provide tools for the localization of events without clear phases or events outside the network, where the station coverage prohibits classical localization techniques. Beam forming allows the determination of the direction (back azimuth) and horizontal (apparent) velocity of...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-08-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/13/1243/2022/se-13-1243-2022.pdf |
| Summary: | <p>Seismic arrays provide tools for the localization of events
without clear phases or events outside the network, where the station
coverage prohibits classical localization techniques. Beam forming allows the
determination of the direction (back azimuth) and horizontal (apparent)
velocity of an incoming wavefront. Here we combine multiple arrays to
retrieve event epicentres from the area of intersecting beams without the
need to specify a velocity model. The analysis is performed in the time
domain, which allows selecting a relatively narrow time window around the
phase of interest while preserving frequency bandwidth. This technique is
applied to earthquakes and hybrid events in the region of Fogo and Brava,
two islands of the southern chain of the Cape Verde archipelago. The results
show that the earthquakes mainly originate near Brava, whereas the hybrid
events are located on Fogo. By multiple-event beam stacking we are able to
further constrain the epicentral locations of the hybrid events in the
northwestern part of the collapse scar of Fogo. In previous studies, these
events were attributed to shallow hydrothermal processes. However, we obtain
relatively high apparent velocities at the arrays, pointing to either deeper
sources or complex ray paths. For a better understanding of possible
errors of the multi-array analysis, we also compare slowness values obtained
from the array analysis with those derived from earthquake locations from
classical (local network) localizations. In general, the results agree well.
Nevertheless, some systematic deviations of the array-derived
back-azimuth and slowness values occur that can be quantified for certain event
locations.</p> |
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| ISSN: | 1869-9510 1869-9529 |