A method of measuring magnetic dissipation on a sub-100 nm scale is presented. This technique relies on measuring changes in the damping of the oscillating tip in a magnetic force microscope (MFM). Damping contrast is strongly correlated with micromagnetic structure and in the case of NiFe, is in quantitative agreement with magnetoelastic losses in the sample. On recording tracks, large damping signals are observed. This has direct consequences on the interpretation of traditional MFM images acquired with detectors that convolute frequency and damping information. © 1997 American Institute of Physics

This study presents observations using new data from a deployment of eight broadband seismometers surrounding a horizontal well pad at distances of~1-3 km for the period before, during, and after a hydraulic fracturing treatment in the Montney Basin, British Columbia, Canada. We use a multistation-matched filter detection and double-difference earthquake relocation to develop a catalog of 350 events associated with hydraulic fracturing stimulation, with magnitudes ranging from −2.8 to 1.8 and estimated catalog completeness of approximately −0.2. The seismicity distribution suggests a statistically significant association with injection, and event migration can be described by a hydraulic diffusivity of~0.2 m 2 /s. A comparison between daily seismicity rate and analytical stress evolution inferred from daily injection volumes implies that pore pressure diffusion largely controls earthquake nucleation at distances less than 1 km, whereas poroelastic stress transfer likely dominates at intermediate distances of~1-4 km at time scales shorter than diffusion. Both mechanisms likely have a limited effect on stress perturbation at distances over 5 km.

Dynamic modeling of sequences of earthquakes and aseismic slip (SEAS) provides a self‐consistent, physics‐based framework to connect, interpret, and predict diverse geophysical observations across spatial and temporal scales. Amid growing applications of SEAS models, numerical code verification is essential to ensure reliable simulation results but is often infeasible due to the lack of analytical solutions. Here, we develop two benchmarks for three‐dimensional (3D) SEAS problems to compare and verify numerical codes based on boundary‐element, finite‐element, and finite‐difference methods, in a community initiative. Our benchmarks consider a planar vertical strike‐slip fault obeying a rate‐ and state‐dependent friction law, in a 3D homogeneous, linear elastic whole‐space or half‐space, where spontaneous earthquakes and slow slip arise due to tectonic‐like loading. We use a suite of quasi‐dynamic simulations from 10 modeling groups to assess the agreement during all phases of multiple seismic cycles. We find excellent quantitative agreement among simulated outputs for sufficiently large model domains and small grid spacings. However, discrepancies in rupture fronts of the initial event are influenced by the free surface and various computational factors. The recurrence intervals and nucleation phase of later earthquakes are particularly sensitive to numerical resolution and domain‐size‐dependent loading. Despite such variability, key properties of individual earthquakes, including rupture style, duration, total slip, peak slip rate, and stress drop, are comparable among even marginally resolved simulations. Our benchmark efforts offer a community‐based example to improve numerical simulations and reveal sensitivities of model observables, which are important for advancing SEAS models to better understand earthquake system dynamics.

Source processes of injection‐induced earthquakes involve complex fluid‐rock interaction often elusive to regional seismic monitoring. Here we combine observations from a local seismograph array in the Montney Formation, northeast British Columbia, and stress modeling to examine the spatiotemporal evolution of the 30 November 2018 Mw 4.2 (ML 4.5) hydraulic fracturing‐induced earthquake sequence. The isolated occurrence of the mainshock at a depth of ∼4.5 km in the crystalline basement 2 days following injection onset at ∼2.5 km depth suggests direct triggering by rapid fluid pressure increase via a high‐permeability conduit. Most aftershocks are in the top 2 km sedimentary layers, with focal mechanisms indicating discrete slip along subvertical surfaces in an ∼1 km wide deformation zone. Aftershock distribution is consistent with static stress triggering from the Mw 4.2 coseismic slip. Our analysis suggests that complex hydraulic and stress transfer between fracture networks needs to be considered in induced seismic hazard assessment.

Over 100 small-to moderate-sized earthquakes, including an Mw 5.0 event, were detected during September 2015 to November 2016 near the town of Cushing, Oklahoma. The seismic sequence was spatial-temporally linked to four wastewater disposal wells within 4 km. We calculate pore pressure and stress perturbations caused by fluid injection at multiple wells and analyze seismic risk in a Coulomb failure stress framework. Despite being more than an order of magnitude smaller than the pore pressure perturbation, the sign of shear stress change, in the sense of assumed right-lateral fault motion, dictates where earthquakes are induced. Most of the relocated earthquakes are located within areas of positive shear stress changes. Our results suggest that poroelastic stress changes also play an essential role in the wastewater disposal environment, and a strategic design of well locations with respect to fault orientation and direction of motion can help mitigate induced seismic hazard. Plain Language Summary Fluid injected into the subsurface is known to induce earthquakes. This study analyzes the relationship between the 2015/2016 Cushing earthquake sequence and wastewater disposal at four wells within 4 km of the sequence. Our results reveal that while pore pressure increase due to fluid diffusion makes the dominant contribution to promote fault slip toward instability, shear stress change in the sense of motion on a preexisting fault is a critical factor that determines where earthquakes can occur. This study suggests that a strategic design of disposal wells locations, with respect to mapped faults, may be an effective way to mitigate injection-induced seismicity.