The search for temporal changes in seismic velocities at Chalk River, Ontario

Imaging and Monitoring Temporal Changes of Shallow Seismic Velocities at the Garner Valley Near Anza, California, Following the M7.2 2010 El Mayor‐Cucapah Earthquake

Journal of Geophysical Research Solid Earth ◽

10.1029/2019jb018070 ◽

2020 ◽

Vol 125 (1) ◽

Cited By ~ 2

Author(s):

Lei Qin ◽

Yehuda Ben‐Zion ◽

Luis Fabian Bonilla ◽

Jamison H. Steidl

Keyword(s):

Temporal Changes ◽

Seismic Velocities ◽

Shallow Seismic

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Regional seismic velocity changes following the 2019 Mw7.1 Ridgecrest California earthquake from autocorrelations and P/S converted waves

Geophysical Journal International ◽

10.1093/gji/ggab350 ◽

2021 ◽

Author(s):

Y Lu ◽

Y Ben-Zion

Keyword(s):

Temporal Resolution ◽

Seismic Velocity ◽

Time Windows ◽

Regional Scale ◽

Early Period ◽

Temporal Changes ◽

High Temporal Resolution ◽

Seismic Velocities ◽

Seismic Velocity Changes ◽

Velocity Changes

Summary We examine regional transient changes of seismic velocities generated by the Mw 7.1 2019 Ridgecrest earthquake in California, using autocorrelations of moving time windows in continuous waveforms recorded at regional stations. We focus on travel time differences in a prominent phase generated by an interface around 2 km depth, associated with transmitted Pp waves and converted Ps waves from the ongoing microseismicity. Synthetic tests demonstrate the feasibility of the method for monitoring seismic velocity changes. Taking advantage of the numerous aftershocks in the early period following the mainshock, we obtain a temporal resolution of velocity changes up to 20 min in the early post-mainshock period. The results reveal regional coseismic velocity drops in the top 1–3 km with an average value of ∼2 per cent over distances up to 100 km from the Ridgecrest event. These average velocity drops are likely dominated by larger changes in the shallow materials, and are followed by rapid recoveries on timescales of days. Around the north end of the Ridgecrest rupture and the nearby Coso geothermal region, the observed coseismic velocity drops are up to ∼8 per cent. The method allows monitoring temporal changes of seismic velocities with high temporal resolution, fast computation, and precise spatial mapping of changes. The results suggest that significant temporal changes of seismic velocities of shallow materials are commonly generated on a regional scale by large events.

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Temporal changes of seismic velocities in the San Jacinto Fault zone associated with the 2016 Mw 5.2 Borrego Springs earthquake

Geophysical Journal International ◽

10.1093/gji/ggz538 ◽

2019 ◽

Vol 220 (3) ◽

pp. 1536-1554 ◽

Cited By ~ 4

Author(s):

Hongrui Qiu ◽

Gregor Hillers ◽

Yehuda Ben-Zion

Keyword(s):

Fault Zone ◽

Temporal Changes ◽

Coda Wave ◽

Seismic Velocities ◽

Rupture Directivity ◽

Lapse Time ◽

Near Surface ◽

Fault Surface ◽

San Jacinto Fault ◽

San Jacinto Fault Zone

SUMMARY We study temporal changes of seismic velocities associated with the 10 June 2016 Mw 5.2 Borrego Springs earthquake in the San Jacinto fault zone, using nine component Green's function estimates reconstructed from daily cross correlations of ambient noise. The analysed data are recorded by stations in two dense linear arrays, at Dry Wash (DW) and Jackass Flat (JF), crossing the fault surface trace ∼3 km northwest and southeast of the event epicentre. The two arrays have 9 and 12 stations each with instrument spacing of 25–100 m. Relative velocity changes (δv/v) are estimated from arrival time changes in the daily correlation coda waveforms compared to a reference stack. The obtained array-average δv/v time-series exhibit changes associated with the Borrego Springs event, superposed with seasonal variations. The earthquake-related changes are characterized by a rapid coseismic velocity drop followed by a gradual recovery. This is consistently observed at both arrays using time- and frequency-domain δv/v analyses with data from different components in various frequency bands. Larger changes at lower frequencies imply that the variations are not limited to the near surface material. A decreasing coseismic velocity reduction with coda wave lapse time indicates larger coseismic structural perturbations in the fault zone and near-fault environment compared to the surrounding rock. Observed larger changes at the DW array compared to the JF array possibly reflect the northwestward rupture directivity of the Borrego Springs earthquake.

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Temporal seismic wave velocity variations at Láscar volcano

Andean geology ◽

10.5027/andgeov43n2-a05 ◽

2016 ◽

Vol 43 (2) ◽

pp. 240 ◽

Cited By ~ 2

Author(s):

Diego M. González ◽

Klaus Bataille ◽

Tom Eulenfeld ◽

Luis E. Franco

Keyword(s):

Seismic Wave ◽

Complex Structure ◽

Temporal Changes ◽

Velocity Variation ◽

Dynamic Processes ◽

Seismic Events ◽

Seismic Velocities ◽

Seismic Wave Velocity ◽

The Earth ◽

Lascar Volcano

We report on the first study using Seismic Wave Interferometry to determine variations of seismic velocities through time, in the vicinity of Láscar volcano in Chile. Seismic Wave Interferometry has been used as a powerful tool to determine spatial and temporal changes of seismic velocities within the Earth. Spatial variations of seismic velocities are related to heterogeneities of material properties, which are expected to occur in a complex structure. However, temporal changes are indicative of dynamic process within the elastic media, and thus, this tool can be used to monitor dynamic processes at volcanic zones. We find consistent variations on three stations close to the volcano, with dv/v of ±0.6%, most likely related to the inflation/deflation process due to fluid movement of magmatic or hydrothermal origin within the volcanic structure. During the observed period of velocity variation, OVDAS reported an increase of volcanic activity evidenced by the increase of the number of long period seismic events, increase of gas emissions and the formation of incandescence above the crater. We suggest that this tool can contribute to the understanding of volcano related dynamic processes, as well as for routine volcano monitoring purposes.

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