On the robustness of seismic moment tensor inversions for mid-ocean earthquakes: the Azores archipelago

Frietsch, Michael; Ferreira, Ana M. G.; Vales, Dina; Carrilho, Fernando

doi:10.1093/gji/ggy294

Cited by 4 publications

(9 citation statements)

References 93 publications

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“…(2)) obtained from the moment tensor inversions of the M w 5.9 Povoação earthquake for the majority of 1-D earth models considered (see Table S4 in the Supporting Information for a list of the source parameters and variance reductions obtained for all 16 models). All the inversions lead to normal faulting focal mechanisms consistent with the solutions obtained by Frietsch et al (2018). Fig.…”

Section: Moment Tensor Inversionssupporting

confidence: 81%

“…While this event did not produce substantial damage (USGS 2017), it was recorded by a number of seismic stations in the region, bringing useful information about the tectonics of the archipelago. In particular, this earthquake exhibited a substantial non-double couple component, which is possibly due to a curved fault in the complex active fault system of the Povoação basin (Weiß et al 2015;Frietsch et al 2018).…”

Section: S E I S M O -T E C T O N I C F E At U R E S O F T H E a Z O mentioning

confidence: 96%

“…The most destructive historical earthquake in the Azores was the 1522 Vila Franca do Campo event in São Miguel Island (Gaspar et al 2015), which had an intensity X (Silveira et al 2003) Miranda et al 2014): the Mid-Atlantic Ridge (MAR), the East Azores Fault Zone (EAFZ), the Princess Alice Rift (PAR), the Terceira Rift (TR) and the region of the Gloria fault (GF). The location and the focal mechanism of the 2013 April 30 M w 5.9 Povoação basin earthquake is also shown (Frietsch et al 2018) along with the seismic stations used in this study (red triangles; the corresponding island is also written in red, with the station name given in brackets). Topography and bathymetry are from SRTM30 PLUS (Becker et al 2009).…”

Section: S E I S M O -T E C T O N I C F E At U R E S O F T H E a Z O mentioning

confidence: 99%

“…1). As mentioned previously, this event is the largest magnitude earthquake that occurred in the Azores Archipelago in the past decade and it produced high-quality waveforms (Frietsch et al 2018). Having evaluated the signal-to-noise ratio across a range of frequency bands, the local seismic waveforms are bandpass filtered in the period range 17-33 s to ensure good quality signals compatible with our modelling.…”

Section: Local Earthquake Datamentioning

confidence: 99%

“…Olsen 2000), as well as for enhanced determinations of earthquake locations and focal mechanisms (e.g. Frietsch et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Crustal structure of the Azores Archipelago from Rayleigh wave ellipticity data

Ferreira

Marignier

Attanayake

et al. 2020

Geophysical Journal International

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SUMMARY Determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings, and to assess seismic hazard in the islands. The Azores Archipelago is located near a triple junction system and is possibly under the influence of a mantle plume, being at the locus of a wide range of geodynamic processes. However, its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands. To address these limitations, in this study we invert teleseismic Rayleigh wave ellipticity measurements for 1-D shear wave speed (VS) crustal models of the Azores Archipelago. Moreover, we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models. We find that data from the westernmost seismic stations used in this study require a shallower Moho depth (∼10 km) than data from stations in the eastern part of the archipelago (∼13–16 km). This apparent increase in the Moho depth with increasing distance from the mid-Atlantic ridge (MAR) is expected. However, the rate at which Moho deepens away from the MAR is greater than that predicted from a half-space cooling model, suggesting that local tectonic perturbations have modified crustal structure. The 1-D VS models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations, which correlates well with the ages of the islands except Santa Maria Island. We interpret the relatively low VS profile found beneath Santa Maria Island as resulting from underplating, which agrees with previous geological studies of the island. Compared to a recent receiver function study of the region, the shallow structure (top ∼2 km) in our models shows lower shear wave speed, which may have important implications for future hazard studies of the region. More generally, the new seismic crustal models we present in this study will be useful to better understand the tectonics, seismicity, moment tensors and strong ground motions in the region.

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Section: Moment Tensor Inversionssupporting

confidence: 81%

Section: S E I S M O -T E C T O N I C F E At U R E S O F T H E a Z O mentioning

confidence: 96%

Section: S E I S M O -T E C T O N I C F E At U R E S O F T H E a Z O mentioning

confidence: 99%

Section: Local Earthquake Datamentioning

confidence: 99%

“…Olsen 2000), as well as for enhanced determinations of earthquake locations and focal mechanisms (e.g. Frietsch et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Crustal structure of the Azores Archipelago from Rayleigh wave ellipticity data

Ferreira

Marignier

Attanayake

et al. 2020

Geophysical Journal International

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Data‐Driven Two‐Fault Modeling of the Mw 6.0 2008 Wells, Nevada Earthquake Suggests a Listric Fault Rupture

2021

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Structural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and deep parts of a listric fault. We use a large data set including 150 local seismic waveforms from the USArray combined with high‐quality Interferometric Synthetic Aperture Radar and teleseismic waveforms. Rather than imposing an a priori fault geometry in the source inversions, as is often done in the literature, we use a data‐driven approach whereby all the faulting parameters and number of faults are determined by the data alone. We find a two‐fault normal faulting solution comprising: (i) a shallow (centroid depth ∼4.6 km) sub‐event with Mw 5.3 and fault dip of ∼77°; and (ii) a deeper (centroid depth ∼8.8 km), larger Mw 6.0 sub‐event on a fault with shallower dip angle (∼41°). Our preferred two‐fault model is consistent with aftershocks and with the tectonics of the region. The local USArray waveforms used in the modeling are key to detect the rupture of both shallow and deep parts of the possible listric fault. The lack of such dense and uniform coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought.

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