Focusing in migration-based location of weak microseismicity: modelling point-spread function for resolution analyses

Lecomte, Isabelle; Lubrano-Lavadera, Paul; Wuestefeld, A.; Kaschwich, Tina; Albaric, Julie; Gharti, Hom Nath

doi:10.1190/segam2015-5813282.1

Cited by 4 publications

(2 citation statements)

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“…To characterize the source imaging resolution, we use Point Spread Functions (PSF), which describe the effect of the imaging system on the imaged object [e.g. Lecomte et al, 2015;Nakahara and Haney, 2015]. The degree of source resolution and illumination may be derived from basic principles of ray theory, by considering the density of source-to-array raypaths.…”

Section: Spatial Resolution Analysismentioning

confidence: 99%

“…As input, we use the spectra of the envelope of the 5 Hz exponentially decaying sine function discussed in the previous section. Equation 2is solved assuming a uniform velocity model of 3.5 km/s, neglecting the effects of scattering on the PSF [Lecomte et al, 2015]. Figure 7 presents the spatial resolution for shallow (10 km; panels a,b) and deep (20 km; panels c,d) sources.…”

Section: -15mentioning

confidence: 99%

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Earthquake Detectability and Depth Resolution with Dense Arrays in Long Beach, California: Further Evidence for Upper-Mantle Seismicity within a Continental Setting

Inbal,

Ampuero,

Clayton

2024

Preprint

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The Newport-Inglewood Fault (NIF) is a slowly-deforming fault cutting through a thin continental crust with a normal geotherm, yet it hosts some of the deepest earthquakes in southern California. The nucleation of deep earthquakes in such a continental setting is not well understood. Moreover, the deep seismogenic zone implies the maximum NIF earthquake magnitude may be larger than expected. Here, we quantify the resolution of the Long-Beach (LB) and the Extended Long-Beach (ELB) dense arrays, used to study deep NIF seismicity. Previous study of the regional catalog and of downward-continued LB array data found NIF seismicity extending into the upper mantle beneath LB. Later studies, which analyzed the ELB raw data, found little evidence for such deep events. To resolve this inconsistency, we quantify the array's microearthquake detectability and resolution power via analysis of pre-and post-downward migrated LB seismograms, and benchmark tests. Downward migration focuses energy onto the source region and de-amplifies the surface noise, thus significantly improving detectability and resolution. The detectability is also improved with the increase in the array-aperture-to-sourcedepth ratio. The LB array maximum aperture is only 20% larger than the ELB aperture, yet its resolution for deep (>20 km) events is improved by about a factor of two, suggesting that small changes to the array geometry may yield significant improvement to the resolution power.Assuming a constant aperture, we find the LB array maintain resolution with 1% of its sensors used for back-projection. However, the high sensor density is essential for improving the SNR.Analysis of the regional and array-derived NIF catalogs together with newly acquired Moho depths beneath the NIF, suggests mantle seismicity beneath LB is a robust feature of this fault.

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Section: Spatial Resolution Analysismentioning

confidence: 99%

Section: -15mentioning

confidence: 99%