Earthquake waveforms recorded at the surface are strongly affected by near-surface processes, including nonlinear wave propagation, scattering, attenuation, topography effects and local noise. These complexities hinder accurate ground motion prediction at the receiver site and obscure weak earthquake signals in surface recordings, especially at high frequencies. Traditional approaches analyze borehole-surface discrepancies to model shallow structures and apply numerical solvers for near-vertical wave propagation. Yet, these attempts are constrained by simplified physical assumptions, high computational costs, and inherent model uncertainties. To address these challenges, we develop U-shaped Neural Operators for Vertical Continuation (UNO-VC), a fully data-driven machine learning framework designed to map seismic waveforms directly through sedimentary layers. UNO-VC facilitates a two-way vertical continuation strategy: (1) upward continuation to predict surface waveforms given bedrock recordings, and (2) downward continuation to back-propagate surface recordings to a bedrock depth, effectively denoising the waveforms for cleaner signals. We apply and test this method on the Garner Valley Downhole Array dataset, which comprises over two decades of high-quality Southern California earthquake recordings. Quantitative analysis demonstrates that UNO-VC outperforms multiple benchmarks. Upward continuation accurately reproduces observed ground motion intensities and waveform shapes; downward continuation yields cleaner earthquake waveforms than raw surface recordings and more detections from an automated phase picker. This framework benefits ground motion prediction and calibration efforts, and mitigates site-effect uncertainties for refined seismic analysis.

An 3 km long nodal array oriented approximately east-west was deployed in Chugiak, Alaska, by the U.S. Geological Survey during 2021. The array intersects with the permanent NetQuakes station NP.ARTY, where peak ground acceleration (PGA) value of 1.98g was recorded during the 2018 Mw 7.1 Anchorage, Alaska, earthquake, in sharp contrast to the PGA of 0.3g at a site just 4 km to the west. Seismic data for ML 1.8-4.3 aftershocks from the Mw 7.1 event recorded by the nodal array confirm the anomalously large ground motions obtained at NP.ARTY as well as similar amplifications at nodes within 1 km to the east. Here, we performed 0-10 Hz 3D finite-difference simulations, including high-resolution surface topography, to explore the cause of the unexpectedly large amplification. As expected, the simulations computed with a regional 3D tomography velocity model severely underpredict the 0-10 Hz acceleration records at almost all sites. Adding a near-surface low-velocity taper to 300 m depth amplifies the accelerations by up to a factor of 5 and enables a reasonable match between the nodal data and simulations at sites to the west of NP.ARTY. However, this model still underpredicts the spectral energy in the area covered by glacial sediments by up to an order of magnitude. The addition of a till layer using a depth-dependent shear-wave velocity (VS) profile along with a homogeneous, 8 m thick low-velocity layer with VS = 250 m=s representing the kame terraces improves the fit to data to within a factor of 2 at nodes located on top of the glacial sediments. Our study shows that the anomalously large high-frequency amplification recorded at and near NP.ARTY can be explained by a combination of topographic effects and near-surface low-velocity material with amplification effects on the high-frequency ground motion by up to about 40% and an order of magnitude, respectively.

Borehole accelerometers are designed to record strong ground movements at depth. They have become an important complement to surface accelerometers for seismic and earthquake engineering applications. Borehole accelerometers present several imple-mentation challenges, including their coupling with the geological environment. One possible coupling solution is the use of small glass beads, which are placed inside the borehole casing with the purpose of filling in any empty space between the sensor and the casing walls. We carried out a test on a shaking table, over a wide range of peak ground accelerations (PGA from 0.17 to 1.64g), allowing the comparison of the sig-nals between a surface accelerometer and a borehole accelerometer coupled through the glass beads. These tests show that there is almost no difference between the surface and borehole accelerometer signals between 0.5 and 25 Hz, and only very small differences outside this band (0.2-0.5 Hz and 25-80 Hz). Furthermore, experience from multiple ver-tical accelerometric arrays show that an installation using glass beads is "reversible", that is, 30 yr after the initial installation it can still be possible to easily extract the acceler-ometers for repair or replacement, without any problems or damage to the sensors.

Subsurface structures play important roles in seismic ground motion, crustal hydrology, stability of the built environment, and more. Constraining temporal changes of subsurface shear wave velocity (V-S) can provide useful information to all these topics and the growing field of hydrological monitoring with seismic velocity. Using borehole records at Garner Valley, CA, we estimate seasonal subsurface V-S variations from impulse response functions (IRFs) of earthquake data (2005-2018) along with IRFs and cross-correlation of cross-hole experiment data (2015-2018). The inferred V-S variations are up to similar to 25% in the top 6 m and similar to 10% at 2-5 m in depth. The V-S variations correlate strongly with the water table depth changes, suggesting that the changes are mostly due to fluctuations of pore pressure in the shallow material. The shallow velocity changes alter the near-surface conditions, can affect seismic hazard estimation, and may be improperly attributed to deeper processes without careful analysis.

We analyze seismograms recorded by four arrays (B1–B4) with 100 m station spacing and apertures of 4–8 km that cross the surface rupture of the 2019 Mw 7.1 Ridgecrest earthquake. The arrays extend from B1 in the northwest to B4 in the southeast of the surface rupture. Delay times between P wave arrivals associated with ∼1,200 local earthquakes and four teleseismic events are used to estimate local velocity variations beneath the arrays. Both teleseismic and local P waves travel faster on the northeast than the southwest side of the fault beneath arrays B1 and B4, but the velocity contrast is less reliably resolved at arrays B2 and B3. We identify several 1–2 km wide low‐velocity zones with much slower inner cores that amplify S waveforms, inferred as damage zones, beneath each array. The damage zones at arrays B2 and B4 also generate fault‐zone head and trapped waves. An automated detector, based on peak ground velocities and durations of high‐amplitude waves, identifies candidate fault‐zone trapped waves (FZTWs) in a localized zone for ∼600 earthquakes at array B4. Synthetic waveform modeling of averaged FZTWs, generated by ∼30 events with high‐quality signals, indicates that the trapping structure at array B4 has a width of ∼300 m, depth of 3–5 km, S wave velocity reduction of ∼20% with respect to the surrounding rock, Q‐value of ∼30, and S wave velocity contrast of ∼4% across the fault (faster on the northeast side). The results show complex fault‐zone internal structures (velocity contrasts and low‐velocity zones) that vary along fault strike.

We derive a detailed earthquake catalogue and V-p,V-s and V-p/V-s models for the region around the 2019 M-w 6.4 and M-w 7.1 Ridgecrest, California, earthquake sequence using data recorded by rapid-response, densely deployed sensors following the Ridgecrest main shock and the regional network. The new catalogue spans a 4-month period, starting on 1 June 2019, and it includes nearly 95 000 events detected and located with iterative updates to our velocity models. The final V-p and V-s models correlate well with surface geology in the top 4 km of the crust and spatial seismicity patterns at depth. Joint interpretation of the derived catalogue, velocity models, and surface geology suggests that (i) a compliant low-velocity zone near the Garlock Fault arrested the M-w 7.1 rupture at the southeast end; (ii) a stiff high-velocity zone beneath the Coso Mountains acted as a strong barrier that arrested the rupture at the northwest end and (iii) isolated seismicity on the Garlock Fault accommodated transtensional-stepover strain triggered by the main events. The derived catalogue and velocity models can be useful for multiple future studies, including further analysis of seismicity patterns, derivations of accurate source properties (e.g. focal mechanisms) and simulations of earthquake processes and radiated seismic wavefields.

Erosion, hydrothermal activity, and magmatism at volcanoes can cause large and unex-pected mass wasting events. Large fluidized debris flows have occurred within the past 6000 yr at Mount Adams, Washington, and present a hazard to communities down-stream. In August 2017, we began a pilot experiment to investigate the potential of infra-sound arrays for detecting and tracking debris flows at Mount Adams. We deployed a telemetered four-element infrasound array (BEAR, 85 m aperture), similar to 11 km from a geo-logically unstable area where mass wasting has repeatedly originated. We present a pre-liminary analysis of BEAR data, representing a survey of the ambient infrasound and noise environment at this quiescent stratovolcano. Array processing reveals near continu-ous and persistent infrasound signals arriving from the direction of Mount Adams, which we hypothesize are fluvial sounds from the steep drainages on the southwest flank. We interpret observed fluctuations in the detectability of these signals as resulting from a combination of (1) wind-noise variations at the array, (2) changes in local infrasound propagation conditions associated with atmospheric boundary layer variability, and (3) changing water flow speeds and volumes in the channels due to freezing, thawing, and precipitation events. Suspected mass movement events during the study period are small (volumes < 10(5) m(3) and durations <2 min), with one of five visually confirmed events detected infrasonically at BEAR. We locate this small event, which satellite imagery suggests was a glacial avalanche, using three additional temporary arrays oper-ating for five days in August 2018. Events large enough to threaten downstream com-munities would likely produce stronger infrasonic signals detectable at BEAR. In complement to recent literature demonstrating the potential for infrasonic detection of volcano mass movements (Allstadt et al., 2018), this study highlights the practical and computational challenges involved in identifying signals of interest in the expected noisy background environment of volcanic topography and drainages.

Earth and Space Science Open Archive This work has been accepted for publication in Journal of Geophysical Research - Solid Earth. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]Detailed seismic imaging of the Mw 7.1 Ridgecrest earthquake rupture zone from data recorded by dense linear arraysAuthorsHongruiQiuiDYehudaBen-ZioniDR. D.CatchingsMark RGoldmanAmirAllamJamisonSteidlSee all authors Hongrui QiuiDCorresponding Author• Submitting AuthorRice UniversityiDhttps://orcid.org/0000-0002-4219-0039view email addressThe email was not providedcopy email addressYehuda Ben-ZioniDUniversity of Southern CaliforniaiDhttps://orcid.org/0000-0002-9602-2014view email addressThe email was not providedcopy email addressR. D. CatchingsU. S. Geological Surveyview email addressThe email was not providedcopy email addressMark R GoldmanUnited States Geological Surveyview email addressThe email was not providedcopy email addressAmir AllamUniversity of Utahview email addressThe email was not providedcopy email addressJamison SteidlEarth Research Institute - UCSBview email addressThe email was not providedcopy email address

The 2019 Ridgecrest, California, earthquake sequence included Mw 6.4 and 7.1 earthquakes that occurred on successive days beginning on 4 July 2019. These two largest earthquakes of the sequence occurred on orthogonal faults that ruptured the Earth’s surface. To better evaluate the 3D subsurface fault structure, (P- and S-wave) velocity, 3D and temporal variations in seismicity, and other important aspects of the earthquake sequence, we recorded aftershocks and ambient noise using up to 461 three-component nodal seismographs for about two months, beginning about one day after the Mw 7.1 mainshock. The ∼30,000Mw≥1 earthquakes that were recorded on the dense arrays provide an unusually large volume of data with which to evaluate the earthquake sequence. This report describes the recording arrays and is intended to provide metadata for researchers interested in evaluating various aspects of the 2019 Ridgecrest earthquake sequence using the nodal data set.

Rapid seismic deployments following large earthquakes capture ephemeral near-field recordings of aftershocks and ambient noise that can provide valuable data for seismological studies. The U.S. Geological Survey installed 19 temporary seismic stations following the 4 July 2019 M w 6.4 and 6 July 2019 (UTC) M w 7.1 earthquakes near the city of Ridgecrest, California. The stations record the aftershock sequence beginning two days after the mainshock and are expected to remain in the field through approximately January 2020. The deployment augments the permanent seismic network in the area to improve azimuthal coverage and provide additional near-field observations. This article summarizes the motivation and goals of the deployment; details of station installation, instrumentation, and configurations; and initial data quality and observations from the network. We expect these data to be useful for a range of studies including detailing near-field variability in strong ground motions, determining stress drops and rupture directivity of small events, imaging the fault zone, documenting the evolution of crustal properties within and outside of the fault zone, and others.

Seismograms from ~700 local earthquakes recorded at various depths (0, 6, 15, 22, 50, and 150 m) by sensors of the Garner Valley Downhole Array in Southern California are used to analyze the shallow velocity structure and temporal changes of seismic velocities after the 2010 M7.2 El Mayor‐Cucapah (EMC) earthquake. The direct P and S wave travel times between surface and borehole stations reveal very low shear wave velocities (178–259 m/s) and very high Vp/Vs ratios (6.2) in the top 22 m. Temporal changes of seismic velocities after the EMC earthquake are estimated using autocorrelations of data in moving time windows at two borehole stations (22 and 50 m) and seismic interferometry between multiple station pairs of the Garner Valley Downhole Array. The S wave velocity in the top 6 m drops abruptly by 14.3 ± 3.3%, during the passage of surface waves from the EMC event with a peak ground acceleration of 39 Gal, and recovers in ~236 s. The average velocity reductions decrease with depth and are 10.9 ± 3.1%, 8.5 ± 2.1%, 6.3 ± 2.1%, and 4.5 ± 2.0% in the top 15, 22, 50, and 150 m, respectively. Comparisons of seismic interferometry results between sensor pairs at 0–22 and 22–150 m indicate that statistically significant velocity changes are limited at the site to the top 22 m. Pore pressure data are in phase with the surface displacement and reach maxima when the highest velocity drop occurs, suggesting fluid effects contribute to the observed velocity reductions.

We present a data set of ground motion recordings and site information from vertical array sites in California. The recordings include two horizontal components of ground shaking at the ground surface level and from downhole sensors. The availability of both surface and downhole recordings at the same site facilitates direct observations of site response. The site data include measured shear- and compression-wave velocities, and, where available, geotechnical boring logs. We considered 39 vertical array sites in California and chose 21 for inclusion in the database on the basis of having at least four pairs of surface/downhole recordings. The recordings and site data are presented in a data repository, which is accessible at the DesignSafe platform (DOI: 10.17603/146DS2N680). The original digital accelerograms are processed in a manner consistent with NGA-West2 protocols. In this paper, this data set is compared to a similar but larger data set from Japanese vertical arrays compiled by others.

The paper discusses the effect of seismic preshaking history on liquefaction of silty sand soils using case histories in California, as well as experimental data. The case histories are: (a) the response of the Wildlife site in the Imperial Valley to the 2010 El-Mayor Cucapah earthquake (M-w = 7.2, a(max) = 0.15g); and (b) the response of the Treasure Island Fire Station (F. S.) site in the San Francisco Bay area to the 1989 Loma Prieta earthquake (M-w = 6.9, a(max) = 0.16g). Both sites are similar in almost every respect except for their seismic history. The magnitude and intensity of the corresponding earthquakes were also very similar at both locations. While Treasure Island F. S. did liquefy during the shaking, Wildlife did not and was far from liquefaction as indicated by piezometers at the site. The experiments conducted in this research were a crude simulation of the seismic history of the sites. From the results of the experimental simulation as well as the field case histories, it is concluded that preshaking by previous earthquakes is the most probable explanation of the higher liquefaction resistance exhibited by the Wildlife site and other sites in the Imperial Valley of Southern California.