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| Titel |
Imaging the crust and the upper mantle using Rayleigh wave ellipticity: Application to Westernmost Iberia |
| VerfasserIn |
Januka Attanayake, Ana M. G. Ferreira |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092751
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| Publikation (Nr.) |
 EGU/EGU2014-7110.pdf |
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| Zusammenfassung |
| Illuminating both earthquake sources and Earth structure is particularly challenging in
regions with sparse seismic networks and unfavourable geographical settings. This is the case
of Portugal, where only a limited number of high quality broadband (BB) seismometers were
available up until recently despite its significant seismic activity and associated
hazards. Examples of significant past events include the devastating great 1755 Lisbon
earthquake (M ~8.5-8.7), the Setúbal event in 1858 (M ~7.1), and the 1909 Benavente
earthquake (M ~6.0). In order to better characterize seismicity in the region and
earthquake source processes, robust and accurate Earth models are needed. The lack
of high quality BB data in the past has hindered quantitative characterization of
regional Earth structure in Portugal. Since 2006, however, a large volume of high
quality BB data is continuously accumulating due to the significant expansion that
Portuguese seismic network has undergone. In the current study, we utilize this
newly available dataset to measure Rayleigh wave ellipticity, which will be inverted
for the seismic structure of the crust and the upper mantle beneath Westernmost
Iberia.
Rayleigh wave ellipticity is commonly defined as the horizontal-to-vertical amplitude
ratio (H/V ratio) at a given seismic station, which theoretically depends only on the structure
beneath that particular station. We are currently measuring H/V ratios for BB stations in
Portugal in the periods ranging from ~25 s to ~200 s that will be inverted for velocity profile
beneath each station. Also, the use of both narrow bandpass filters and a multitaper method to
make H/V ratio measurements is currently being explored. We carry out extensive synthetic
tests using theoretical seismograms calculated from normal mode summation in the
epicentral distance range [40°, 65°] for the Preliminary Reference Earth Model
(PREM), considering the effects of fundamental and higher modes on the H/V ratio
estimates. Our initial synthetic tests produce stable H/V ratios with little scatter over all
frequencies and distances considered, indicating reliability of our measurement technique.
Constraining Earth structure based on the H/V measurements is currently underway. |
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