James Phillip Verdon

Microseismic monitoring is often used at subsurface industrial sites, such as hydraulic fracturing for shale gas, stimulation of engineered geothermal systems, mature hydrocarbon reservoirs, and carbon capture and storage. Microseismic observations can be used to map growing fractures in the subsurface, to understand the geomechanical response of subsurface reservoirs to industrial operations, and to identify and characterize nascent induced seismicity. Downhole microseismic datasets are acquired using multistation geophone strings placed in deep boreholes at reservoir depths, with sampling rates at 1 kHz or higher. Artificial intelligence (AI) tools have driven a step-change in the processing of surface-based seismological data. However, similar improvements are yet to be realized for downhole microseismic processing tasks. To date, a major barrier in the development of AI tools for downhole microseismic monitoring has been the lack of publicly available data with which to train models. We seek to eliminate this barrier by curating an AI-ready downhole microseismic benchmark database (AMBER) consisting of waveforms and labels (arrival time picks) drawn from 10 downhole microseismic datasets. AMBER contains over 4,000 events with over 150,000 individual P and S wave picks. All picks have been manually verified. The database also contains over 10,000 examples of signal-free noise, which have also been manually verified. The database is provided in an AI-ready format, with Python functions for data ingestion and data augmentation. It is hoped that AMBER will stimulate and support the development of AI tools for downhole microseismic processing.

Induced seismicity associated with fluid injection in Enhanced Geothermal Systems (EGS) represents one of the main challenges for the development of geothermal energy. The accurate characterization of pre-existing fault structures at reservoir depth is essential for understanding the seismic response to hydraulic stimulation and for mitigating the associated risks. This study investigates the seismogenic sources activated during the 2021 hydraulic stimulation campaign at the Gonghe EGS site (NE Tibetan Plateau, China), using a dataset of 204 microseismic events with ML larger than 0.7, recorded by a temporary, non-optimised surface network. A multi-method analytical approach combining waveform cross-correlation, hierarchical clustering, double-difference relocation (HypoDD), Principal Component Analysis (PCA), and shear wave splitting (SWS) is applied to characterize the geometry and anisotropic fabric of the activated structures. Three fault families are identified, with NNE (strike 22.5° ± 1.5°, dip 62.7°), WNW (strike 285.6° ± 10.6°, dip 79.0°), and NNW (strike 327.9° ± 2.2°, dip 76.1°) orientations, all consistent with strike-slip kinematics. The identified structures are consistent with pre-existing discontinuities documented by previous studies in the area, supporting the interpretation that fluid injection preferentially reactivated pre-existing faults rather than generating new fractures. SWS analysis also reveals a dominant fast polarization direction of ~38°, broadly consistent with the regional maximum horizontal stress SHmax of NE55° in the area. The results confirm that multi-method integration can provide reliable structural characterization of deep seismogenic sources even under non-optimal monitoring conditions and offer direct indications for optimizing future network geometry to improve subsurface imaging.

The ML 5.6 mainshock within the Reno earthquake sequence in northern Alberta represents the largest induced event in Canada and is among the largest such events globally. We use seismological observations from local monitoring arrays deployed 6 days after the mainshock to develop a detailed understanding of the processes that drove the seismicity and relationships with nearby wastewater disposal (WWD) wells. The seismicity maps out a single fault plane located entirely within the crystalline basement. We used reflection seismic datasets to identify fault structures in the sedimentary section, which could have provided pathways for pressure transfer downward to the reactivated fault plane, and mapped a fault extending from the Belloy Formation down to the basement. If extrapolated through the basement, this structure connects to the position on the mainshock fault plane where the seismicity was densest during the early stages of monitoring. Therefore, this structure represents the most likely conduit for downward pressure transfer from WWD. As mapped in the sedimentary section, it extends through the Belloy and Leduc Formations (the two main targets for WWD), and so pressure could have been transferred from WWD in both formations. However, there is statistically significant temporal correlation between the seismicity and operations in a nearby well in the Belloy Formation, whereas there is no temporal correlation with operations in the nearby Leduc well. The existence of temporal correlation and the spatial proximity of the mapped fault to the Belloy well lead us to conclude that the Belloy well has a stronger connection to the Reno induced seismicity.

Scientific exploration of the UK and Ireland's subsurface has made important contributions to scholarship and prosperity for people and the planet, including economic growth, sustainable use of natural resources, storage of greenhouse gases, and inspiring curiosity about the Earth beneath our feet. This article outlines a vision for an array of seismological instruments spanning the UK and Ireland, UKI Array, augmented by other types of geophysical sensors, to maximise the value offered by existing equipment pools. The mission is to research natural phenomena and structure in the deep and shallow Earth, to solve problems concerning hazards and resources, to connect scientists to schools and the broader public, and thus to inspire a new generation to learn about geophysics. The vision was created through a community driven process of engagement and participation. This paper describes the concept and design of the UKI-Array; a companion paper discusses related opportunities and potential applications.

In this paper we document the first example‐the southern Delaware Basin‐where widespread induced triggered (as opposed to “driven”) seismicity across a large area exhibits a maximum magnitude truncation. The most likely cause of this truncation is that although the shallow faults in this area are many km in length, they are structurally constrained and have limited down‐dip widths, typically no more than approximately 1 km. Ruptures on faults of such limited width are not expected to attain high aspect ratios. As such, the ruptures on such faults would be limited to dimensions of roughly 1 km ² , which corresponds to magnitudes which closely match the observed M _MAX truncation. The M _MAX truncation for induced earthquakes in the southern Delaware Basin has significant implications since it implies that down‐dip fault widths may play an important role in constraining the maximum magnitudes of induced events.

DL-based earthquake detection can detect substantially more induced microseismic events than conventional detection methods, revealing finer-scale patterns of hydraulic fracturing-induced seismicity (HFIS). We implement a novel workflow for the Preston New Road-1z (PNR-1z) shale gas site, UK, that integrates DL phase picking, Oct-Tree-based phase association, and probabilistic non-linear location to generate a high-resolution “deep” seismic catalogue from a single high-frequency (2000 Hz) borehole array. PhaseNet has detected 11,021 previously undetected events (49,472 events total), compared to the previous catalogue, in which 38,452 events were identified by a beamforming method. We find that the enhanced catalogue increases event cluster densities by an average of 42% and lowers the magnitude of completeness (M _c ) from -0.2 to -0.5, adding thousands of additional events to Gutenberg-Richter b-value analyses. The spatial patterns suggest that HFIS interacted with a fault or fracture zone north of the PNR wells, contrasting with previous event locations and their interpretations. Combining the largest and best recorded events, using locations from our independently derived catalogue, with 3D seismic reflection data reveals clustering along previously unmapped seismic discontinuities ~300 m north of the injection wells, indicating strong structural controls on HFIS. In addition, we re-estimate moment magnitudes (M _w ) using continuous downhole waveforms, finding that magnitudes reported in the previous operational catalogue were systematically underestimated by an average of 0.93 units. The temporal b-values revealed higher b-values during active injection, consistent with tensile HF-dominated microseismicity, and relatively lower b-values during pauses and certain mid-stages, indicating increased shear failure and interaction with a pre-existing fracture zone. The deep catalogue allows for more robust b-value estimation and temporal tracking, potentially reflecting evolving source characteristics and fluid-driven processes during stimulation. This study demonstrates that DL-enhanced catalogues can refine subsurface interpretations, identify re-activated structures efficiently, and contribute to improved hazard assessments in geo-energy systems.

The ML 5.6 mainshock within the Reno earthquake sequence in northern Alberta represents the largest induced event in Canada, and is among the largest such events globally. We use seismological observations from local monitoring arrays to develop a detailed understanding of the processes that drove the seismicity and relationships with nearby wastewater disposal (WWD) wells. The seismicity maps out a single fault plane located entirely within the crystalline basement. We used reflection seismic datasets to identify fault structures in the sedimentary section which could have provided pathways for pressure transfer downward to the reactivated fault plane, and mapped a fault extending from the Belloy Formation to the shallowest part of the mainshock fault. The mapped fault connects to the position on the mainshock fault plane where the seismicity was densest during the early stages of monitoring. This structure therefore represents the most likely conduit for downward pressure transfer from WWD. As mapped in the sedimentary section, it extends through the Belloy and Leduc Formations (the two main targets for WWD), and so pressure could have been transferred from WWD in both formations. However, there is statistically significant temporal correlation between the seismicity and operations in a nearby well in the Belloy Formation, whereas there is no temporal correlation with operations in the nearby Leduc well. The existence of temporal correlation, and the spatial proximity of the mapped fault to the Belloy well, lead us to conclude that the Belloy well has a stronger connection to the Reno induced seismicity.

Advanced seismicity monitoring is needed for CO₂ sequestration monitoring. Current regulator practices (so‐called traffic light systems—TLS) are limited to mitigate public hazards and associated risks caused by induced seismicity. Such seismicity is often associated with slip on larger faults below the reservoir. We propose an advanced seismic monitoring strategy that not only accounts for felt seismicity but also targets seismicity in the seal and reservoir. This novel concept of tiered seismicity criteria for an advanced seismic monitoring strategy is governed by a storage site's specific geological properties (underburden, reservoir and seal). These observed seismicity criteria can be set by the regulator or operator to develop a corresponding and fit for purpose system that further manages induced seismicity to ensure seal integrity and storage longevity.

We explore the performance of distributed acoustic sensing (DAS) for crosswell seismic imaging at a shallow geothermal project in an abandoned mine. The UK Geoenergy Observatory (UKGEOS) research facility in Glasgow has repurposed an abandoned coal mine below the city with the goal to investigate the heat storage and heat recovery potential of flooded mines. Originally for distributed temperature sensing purposes, UKGEOS installed fiber-optic cables in boreholes less than 100 m deep passing through the mined coal seams now targeted for heat production. We first conduct a crosswell active-source seismic survey prior to heat pump installation to obtain a baseline velocity structure of the coal seams and surrounding lithologies. We acquire data simultaneously with DAS and a colocated hydrophone array to facilitate a comparison with conventional crosswell methods. We find that the noise levels are significantly higher for DAS, making first arrivals discernible only within a 30 m vertical offset between shot and channel depths, which limits the DAS monitoring depth range along the borehole. However, the DAS coda provides much greater spatial resolution that can capture refracted arrivals, allowing for accurate and precise identification of discrete layers. Future repeated surveys with DAS can thus shed important light on any changes within the seismic velocity structure between the boreholes, indicating potential changes in fracture zones and fluid pathways. Just as repurposing abandoned coal mines for geothermal energy has been shown to be a promising alterative geoenergy source, DAS could be an inexpensive and simpler alternative to drilling monitoring wells and deploying conventional seismic arrays.