Adam Patrick Young

Seismic velocity models are effective for imaging subsurface structures, yet resolving shallow features at depths less than 100 m remains challenging due to the limited availability of high-frequency signals and the need for closely spaced channels. We addressed this using distributed acoustic sensing (DAS) to image the near-surface seismic structure at high resolution, using train traffic recorded along a 14.7 km buried fiber-optic cable in Del Mar, California. The study area includes unstable coastal cliffs, where subsurface conditions vary due to differences in geologic composition and ongoing erosion. Using interferometry on train-passing recordings, we computed cross-correlation functions, estimated Rayleigh-wave phase velocities through beamforming, and inverted for 1D shear-wave velocity (VS) at each channel, which were then assembled into a 2D tomographic VS profile along the fiber. The resulting 2D VS profile reveals key geologic features, including low-velocity zones in the San Dieguito Valley and Los Peñasquitos Lagoon, corresponding to thicker alluvial and lagoonal sediments. The average VS in the upper 30 m depth (VS30) shows a strong correlation with elevation, and the low VS30 at the coastal cliff is associated with sand content and sediment thickness. In addition, diurnal strain patterns recorded by DAS indicate sensitivity to temperature variations and may help identify fiber spool locations. The VS model demonstrates the potential of DAS to provide high-resolution, cost-effective subsurface imaging and environmental monitoring in complex coastal settings.

Recent Lake Cahuilla has undergone repeated filling and drying cycles over the past millennium, resulting in lithospheric and mantle loading responses. Two critical but less well‐constrained factors influencing these responses are the elastic plate thickness and mantle relaxation time. Using high‐resolution LiDAR surveys and GPS vertical velocity data, we refine estimates of present‐day shoreline elevations and invert for these geophysical parameters. The integration of LiDAR‐derived shoreline data provides a more detailed understanding of shoreline elevation and its variability than had been possible from previous studies. Long‐term vertical velocities from GPS stations help constrain the extent of any ongoing rebound associated with past water loads. Applying a viscoelastic rebound model, we estimate the plate thickness and mantle relaxation time that best explain the observed shoreline features. Our analysis reveals a model with an elastic thickness of 30 [±2] km and a mantle relaxation time of 25 [+10, −6] years that best represents vertical motions in the Earth's crust, offering new insights into the region's geodynamic processes. Our best fit model suggests that uplift in areas around the Salton Sea can potentially be as high as several centimeters over the course of several relaxation times (150 years) if the Salton Sea were drawn down completely.

Coastal cliffs shape the world's coastlines, providing areas of beauty, habitat, scientific discovery, and recreation. However, as erosional features, coastal cliffs can pose fatal hazards. This paper presents a database of global fatal coastal cliff and slope failures from public databases and media articles. In total, the fatal coastal cliff failure database includes 292 fatalities resulting from 114 events from 1927–2024. Cliff failure events occurred in 32 countries, with the most events in Spain (20), the United States (19), France (14), and the United Kingdom (10), including 10+ event hot spots on both Réunion Island, France, and in San Diego County, California, USA. Most fatalities occurred in temperate regions, with about half of events occurring with 30 d antecedent precipitation below average, differing from databases that include non-coastal fatal landslide events driven largely by rainfall. The database is likely incomplete, and we caution tested relationships on incomplete data; however, the present results suggest that the timing of coastal fatal cliff failures may be influenced by (a) elevated rainfall causing reduced cliff stability, leading to failures in wet seasons and (b) time periods of increased tourism and recreational beach activity, exposing more people to coastal cliff failure hazards in relatively dry seasons. The results can help inform beach hazard management.

A 7‐year coastal cliff erosion record, developed from 320 ∼weekly LiDAR surveys of a 2.3 km‐long cliff in southern California, is used to examine the cliff geomorphological response to the variability of environmental forcing (water level, waves, rain, and groundwater) from weekly to interannual timescales at different cliff elevations. When the environmental factors were considered independently, the erosion of the lower‐cliff within the wave exposure zone best correlated with wave forcing ( r ² = 0.38) at weekly scales, while the upper‐cliff correlated best with rain ( r ² = 0.36) and groundwater ( r ² = 0.15). Higher correlations were found when considering combined environmental forcing, with the greatest lower/upper‐cliff geomorphological response to combined environmental changes at semiannual/monthly timescales, respectively ( R ² = 0.66/ R ² = 0.58). A wave‐forcing increase of 36% relative to the monthly climatology was observed during El Niño, coinciding with increased cliff‐erosion activity. Multi‐variable seasonal cliff erosion models accounting for the combined effects of environmental forcing captured the interannual variability in cliff erosion but presented limitations in capturing episodic cliff failure events. The results indicate that large‐scale interannual climate patterns, such as ENSO influence on wave forcing on cliffs at the study site, should be considered in rock coast evolution modeling.

Coastal landslides threaten communities, cultural and recreational lands, infrastructure and public safety. To better understand the landslide hazard zone on the beach, this study used historical failures to measure the landslide runout distance from the cliff toe. Landslide debris on the beach was mapped for a 30 km study area in northern San Diego County, California using over 700 LiDAR and photogrammetric surveys collected between 2002 and 2023. The results provide a unique statistical database of coastal landslide runout observations. The maximum, mean and median runout distances were 36.2 m, 6.0 m and 4.9 m, respectively. Most runout was constrained relatively close to the cliff, with 90% of all runout distances less than 13 m. Results indicate that taller cliffs generated larger maximum runout distances and that a maximum runout of one half the cliff height accounted for 98.5% of the observations. The observed runout distances and statistics can help inform mapping of coastal hazard zones, improve public safety measures, and also improve geomorphic models of cliff retreat.

Coastal cliff failures pose significant risks to public safety and coastal infrastructure, especially in southern California. We deployed a suite of continuous geophysical sensors to investigate failure processes and precursory behaviors at three coastal clifftop sites in San Diego County: San Elijo State Beach and two locations in Del Mar. Our sensors captured baseline and pre‐failure signals, and cliff collapses, revealing patterns in ground deformation leading up to failure. Across all sites, we observed stages of accelerating ground displacement corresponding to the creep stage of imminent failure. Inconsistent best‐fit functions highlight the complexity of cliff failure dynamics while velocity and acceleration relationships and inverse velocity provide more reliable indicators of imminent collapse, aligning with established slope failure models. Cliff failures often occur following storms, highlighting the influence of environmental factors, particularly rainfall, on erosion, instability, and failure. These findings demonstrate the benefits of continuous geophysical monitoring for characterizing cliff instability in near real‐time and provide valuable insights for hazard mitigation and early warning applications.

Coastal cliffs shape the world’s coastlines, providing areas of beauty, habitat, scientific discovery, and recreation. However, as erosional features, coastal cliffs can also pose fatal hazards. This paper presents a database of global fatal coastal landslides from public databases and media articles. In total, the coastal landslide database includes 292 fatalities resulting from 114 landslide events from 1927–2024. Landslide events occurred in 32 countries, with the most events in Spain (20), the United States (19), France (14), and the United Kingdom (10), and include two 10-event hot spots on Reunion Island, France, and San Diego County, California, USA. Most fatalities occurred in temperate regions, with about half of events occurring during months with above average precipitation (and half below), differing from databases that include non coastal fatal landslide events driven largely by rainfall. The database is likely incomplete in part from reporting bias, and the analysis presented here should be interpreted with caution. However, the present results suggest that the timing of coastal fatal landslides may be influenced by (a) elevated rainfall causing reduced cliff stability, leading to more failures in wet seasons and (b) time periods of increased tourism and recreational beach activity, exposing more people to coastal cliff failure hazards in relatively dry seasons. The results can help inform beach hazard management.

Coastal cliffs shape the world’s coastlines, providing areas of beauty, habitat, scientific discovery, and recreation. However, as erosional features, coastal cliffs can also pose fatal hazards. This paper presents a database of global fatal coastal landslides from public databases and media articles. In total, the coastal landslide database includes 292 fatalities resulting from 114 landslide events from 1927–2024. Landslide events occurred in 32 countries, with the most events in Spain (20), the United States (19), France (14), and the United Kingdom (10), and include two 10-event hot spots on Reunion Island, France, and San Diego County, California, USA. Most fatalities occurred in temperate regions, with about half of events occurring during months with above average precipitation (and half below), differing from databases that include non coastal fatal landslide events driven largely by rainfall. The database is likely incomplete in part from reporting bias, and the analysis presented here should be interpreted with caution. However, the present results suggest that the timing of coastal fatal landslides may be influenced by (a) elevated rainfall causing reduced cliff stability, leading to more failures in wet seasons and (b) time periods of increased tourism and recreational beach activity, exposing more people to coastal cliff failure hazards in relatively dry seasons. The results can help inform beach hazard management.

Coastal cliffs shape the world’s coastlines, providing areas of beauty, habitat, scientific discovery, and recreation. However, as erosional features, coastal cliffs can also pose fatal hazards. This paper presents a database of global fatal coastal landslides from public databases and media articles. In total, the coastal landslide database includes 292 fatalities resulting from 114 landslide events from 1927–2024. Landslide events occurred in 32 countries, with the most events in Spain (20), the United States (19), France (14), and the United Kingdom (10), and include two 10-event hot spots on Reunion Island, France, and San Diego County, California, USA. Most fatalities occurred in temperate regions, with about half of events occurring during months with above average precipitation (and half below), differing from databases that include non coastal fatal landslide events driven largely by rainfall. The database is likely incomplete in part from reporting bias, and the analysis presented here should be interpreted with caution. However, the present results suggest that the timing of coastal fatal landslides may be influenced by (a) elevated rainfall causing reduced cliff stability, leading to more failures in wet seasons and (b) time periods of increased tourism and recreational beach activity, exposing more people to coastal cliff failure hazards in relatively dry seasons. The results can help inform beach hazard management.