High-precision earthquake locations in Switzerland using regional secondary arrivals in a 3-D velocity model

Wagner, Michael J.; Husen, Stephan; Lomax, Anthony; Kissling, Edi; Giardini, Domenico

doi:10.1093/gji/ggt052

Cited by 23 publications

(20 citation statements)

References 40 publications

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“…In the last two decades, the increased availability of subsurface data from geological and geophysical studies has allowed the construction of very detailed 3‐D velocity models for earthquake location. In some cases, controlled source seismic data are merged with passive tomographic models to constrain the structure of the main velocity discontinuities [e.g., Husen et al ., ; Wagner et al ., ]. In other studies, the seismic velocities from both commercial seismic lines and sonic logs [e.g., Cushing et al ., ] or from passive tomographic inversion [e.g., Bethoux et al ., ] are integrated into geological models to construct reliable velocity models.…”

Section: Introductionmentioning

confidence: 99%

Assessment of earthquake locations in 3‐D deterministic velocity models: A case study from the Altotiberina Near Fault Observatory (Italy)

et al. 2016

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The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high‐resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three‐dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, six deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P and S wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a nonlinear, global‐search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher‐quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.

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Section: Introductionmentioning

confidence: 99%

Assessment of earthquake locations in 3‐D deterministic velocity models: A case study from the Altotiberina Near Fault Observatory (Italy)

et al. 2016

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“…For instance, 3-D earth models can be used to improve the accuracy of earthquake location (e.g. Chen et al 2006;Wagner et al 2013) or moment tensor inversion (e.g. Hingee et al 2011), the results of which are key for understanding seismotectonics and assessing earthquake hazard.…”

Section: Introductionmentioning

confidence: 99%

“…However, several studies have shown that the use of 3-D earth models has the potential to improve the accuracy of earthquake parameters, particularly in regions where the Earth displays strong lateral heterogeneities (e.g. Husen et al 2003;Hingee et al 2011;Wagner et al 2013;Béthoux et al 2016). In Earth structure studies, high-resolution 3-D seismic models are useful starting models.…”

Section: Introductionmentioning

confidence: 99%

PRISM3D: a 3-D reference seismic model for Iberia and adjacent areas

Arroucau

Custódio

Civiero

et al. 2021

Geophysical Journal International

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SUMMARY We present PRISM3D, a 3-D reference seismic model of P- and S-wave velocities for Iberia and adjacent areas. PRISM3D results from the combination of the most up-to-date earth models available for the region. It extends horizontally from 15°W to 5°E in longitude, 34°N to 46°N in latitude and vertically from 3.5 km above to 200 km below sea level, and is modelled on a regular grid with 10 and 0.5 km of grid node spacing in the horizontal and vertical directions, respectively. It was designed using models inferred from local and teleseismic body-wave tomography, earthquake and ambient noise surface wave tomography, receiver function analysis and active source experiments. It includes two interfaces, namely the topography/bathymetry and the Mohorovičić (Moho) discontinuity. The Moho was modelled from previously published receiver function analysis and deep seismic sounding results. To that end we used a probabilistic surface reconstruction algorithm that allowed to extract the mean of the Moho depth surface along with its associated standard deviation, which provides a depth uncertainty estimate. The Moho depth model is in good agreement with previously published models, although it presents slightly sharper gardients in orogenic areas such as the Pyrenees or the Betic-Rif system. Crustal and mantle P- and S-wave wave speed grids were built separately on each side of the Moho depth surface by weighted average of existing models, thus allowing to realistically render the speed gradients across that interface. The associated weighted standard deviation was also calculated, which provides an uncertainty estimation on the average wave speed values at any point of the grid. At shallow depths (<10 km), low P and S wave speeds and high VP/VS are observed in offshore basins, while the Iberian Massif, which covers a large part of western Iberia, appears characterized by a rather flat Moho, higher than average VP and VS and low VP/VS. Conversely, the Betic-Rif system seems to be associated with low VP and VS, combined with high VP/VS in comparison to the rest of the study area. The most prominent feature of the mantle is the well known high wave speed anomaly related to the Alboran slab imaged in various mantle tomography studies. The consistency of PRISM3D with previous work is verified by comparing it with two recent studies, with which it shows a good general agreement.The impact of the new 3-D model is illustrated through a simple synthetic experiment, which shows that the lateral variations of the wave speed can produce traveltime differences ranging from –1.5 and 1.5 s for P waves and from –2.5 and 2.5 s for S waves at local to regional distances. Such values are far larger than phase picking uncertainties and would likely affect earthquake hypocentral parameter estimations. The new 3-D model thus provides a basis for regional studies including earthquake source studies, Earth structure investigations and geodynamic modelling of Iberia and its surroundings.

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“…If available, ground‐truth sources, such as artificial explosions with known locations or natural events with hypocenters highly constrained by a dense local network, are used to calibrate arrival‐time corrections (e.g., Bondár et al, , ; Bondár & McLaughlin, ). Additional approaches to improving absolute event locations include using stations close to or above the target source zone (e.g., Darold et al, ; Eaton et al, ); adding additional constraint, especially for depth control, from secondary phases such as Moho reflections (regional ‐ Wagner et al, ) or depth phases (teleseismic ‐ Engdahl et al, ); obtaining a centroid depth from CMT waveform inversion (Engdahl et al, ), which may be quasi‐independent of the arrival‐time location depth, but which depends on the velocity model; or using the zone of greatest intensity of shaking as a proxy for an epicentral location (e.g., Holland, ). In practice, a combination of these may be best, although in general, use of ground‐truth sources is considered the best approach and a necessary component for improving accuracy of absolute seismic‐event locations.…”

Section: Introductionmentioning

confidence: 99%

Improving Absolute Earthquake Location in West Texas Using Probabilistic, Proxy Ground‐Truth Station Corrections

Lomax¹,

Savvaidis

2019

JGR Solid Earth

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An increase in induced seismicity in the central United States since 2009 led to establishment of TexNet seismic-monitoring in Texas. Accurate, absolute seismic-event location is critical to TexNet, allowing quantitative evaluation of possible association of seismicity with human activity. For the Delaware Basin, western Texas, relocation using different velocity models and TexNet station subsets shows absolute location error up to 4-5 km. The preferred method to reduce absolute error, ground-truth calibration, is not available in this area. Alternatively, we used industrial well activity as proxy, ground-truth for developing probabilistic, proxy ground-truth (PPGT) station corrections for relocation. Assuming well activity causes seismicity, we defined a distance-time probability associating events and well activity. We used these associations and other evidence to show some seismicity in the Delaware Basin is more likely due to hydraulic-fracturing than saltwater disposal. We then probabilistically accumulated PPGT station corrections using event hypocenters constrained to associated fracturing-well locations. We applied this procedure within 12 km of TexNet station PB02, optimizing the procedure through comparison of rates of causal and acausal associations. Relative to the initial locations, final PPGT relocations show smaller residuals and shifts in epicenter as much as 3 km, predominantly toward the north and northwest. PPGT residuals are similar to those from relocation with standard station corrections. The initial hypocenters showed an unreasonable deepening with distance from station PB02, whereas PPGT relocations produced an overall flattening of event depths. These results are consistent with PPGT corrections giving real improvement in absolute location accuracy.Plain Language Summary The TexNet seismic-monitoring program in Texas was established in response to an increase in human-induced earthquakes in the central United States since 2009. Accurate determination of the geographic location and depth in the Earth of earthquakes is critical to TexNet monitoring, allowing potential association of earthquakes with human activity. But accurately locating earthquakes is difficult due to lack of geologic knowledge and sparsity of seismic monitoring stations. For a study area in western Texas, errors in TexNet earthquake location and depth may be as much as 4-5 km. Ideally, accuracy would be improved by calibration of the seismic network using ground-truth seismic events, such as quarry blasts, but such information is unavailable in this area. Instead, assuming that some earthquakes could be caused by hydraulic-fracturing in the study area, we statistically associate earthquakes in space and time to fracturing activity. We then use the known locations of this associated activity as proxy ground-truth to calibrate the seismic network. Our results suggest some earthquakes in west Texas are more likely due to hydraulic-fracturing than saltwater disposal. Quality measures and spatial patterns of earthquakes relo...

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High-precision earthquake locations in Switzerland using regional secondary arrivals in a 3-D velocity model

Cited by 23 publications

References 40 publications

Assessment of earthquake locations in 3‐D deterministic velocity models: A case study from the Altotiberina Near Fault Observatory (Italy)

Assessment of earthquake locations in 3‐D deterministic velocity models: A case study from the Altotiberina Near Fault Observatory (Italy)

PRISM3D: a 3-D reference seismic model for Iberia and adjacent areas

Improving Absolute Earthquake Location in West Texas Using Probabilistic, Proxy Ground‐Truth Station Corrections

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