Debris flows are concentrated slurries of water and sediment that shape the landscape and pose a major hazard to human life and infrastructure. Seismic ground motion‐based observations promise to provide new, remote constraints on debris flow physics, but the lack of data and a theoretical basis for interpreting them hinders progress. Here we present a new mechanistic physical model for the seismic ground motion of debris flows and apply this to the devastating debris flows in Montecito, California on 9 January 2018. The amplitude and frequency characteristics of the seismic data can distinguish debris flows from other seismic sources and enable the estimation of debris‐flow speed, width, boulder sizes, and location. Results suggest that present instrumentation could have provided 5 min of early warning over limited areas, whereas a seismic array designed for debris flows would have provided 10 min of warning for most of the city.

At the core‐mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab‐like structures beneath the mid‐Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS‐complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone ~200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted Sdiff waveforms further reveal patches interrupted by observed enhanced D″ indicative of slab‐debris influence on the complexity of the northeastern boundary of the mid‐Pacific LLSVP.

The Geysers geothermal field is one of the most seismically active regions in northern California. Most of the events occur at shallow depths and are related to stress and hydrological perturbations due to energy production operations. To better understand the relationships between seismicity and operations, better source mechanism information is needed. Seismic moment tensors offer insight into the nature of equivalent forces causing the seismicity. Fifty-three M >3 events located at The Geysers geothermal field were selected from the University of California Berkeley Moment Tensor Catalog for analysis of seismic moment tensor solutions and associated uncertainties. Deviatoric and full moment tensor solutions were computed, and statistical tests were employed to assess solution stability, resolution, and significance. In this study, we examine several source models including double-couple (DC), pure isotropic (ISO; volumetric change), and volume-compensated linear vector dipole (CLVD) sources, as well as compound sources such as DC CLVD, DC ISO, and shear-tensile sources. In general, we find from a systematic approach toward characterizing uncertainties in moment tensor solutions that The Geysers earthquakes, as a population, deviate significantly from northern California seismicity in terms of apparent volumetric source terms and complexity.

We conducted an experiment in Pahrump, Nevada, in June 2017, where artificial seismic signals were created using a seismic hammer, and the possibility of detecting them from their acoustic signature was examined. In this work, we analyze the pressure signals recorded by highly sensitive barometers deployed on the ground and on tethers suspended from balloons. Our signal processing results show that wind noise experienced by a barometer on a free‐flying balloon is lower compared to one on a moored balloon. This has never been experimentally demonstrated in the lower troposphere. While seismoacoustic signals were not recorded on the hot air balloon platform owing to operational challenges, we demonstrate the detection of seismoacoustic signals on our moored balloon platform. Our results have important implications for performing seismology in harsh surface environments such as Venus through atmospheric remote sensing.

The mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere. We numerically simulate this coupled system for two application cases: active seismic experiments (ASEs) and passive seismic experiments. A recent ASE (Krishnamoorthy et al., 2018, https://doi.org/10.1002/2018GL077481) observed the infrasonic signals produced by a seismic hammer. To measure the sensitivity of observations to seismic parameters, we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock‐solid subsurface. At long range, we investigate the influence of the source by using two focal mechanisms. We found surface waves generate an infrasonic plane head wave in the ASE case of the rock‐solid material. For the passive seismic experiments, the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail. Despite some limitations, the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties.