About

Jonathan Ajo-Franklin is a professor in the Department of Earth, Environmental and Planetary Sciences at Rice University. His research focuses on solving challenging problems related to environmental and energy systems through applied geophysics. His work aims to advance seismic acquisition and monitoring techniques to better understand subsurface fluid flow, fracture mechanics, stress perturbations, and phase changes. A central theme of his research involves using seismology to address issues at the interface between human activity and the subsurface, including CO2 mitigation, energy production in a carbon-constrained world, management of scarce water resources, and understanding the impact of climate change on subsurface systems such as permafrost stability and the weathering cycle. His technical approach employs a diverse set of methods, notably utilizing distributed fiber optic sensing, particularly distributed acoustic sensing (DAS), to enable dense large aperture seismic recording. He explores leveraging unused telecommunications infrastructure, such as dark fiber, as seismic sensors and investigates the use of permanent seismic sources for timelapse imaging with high sensitivity and short repeat times. When active sources are unavailable, he works on utilizing ambient seismic wavefield noise for imaging applications. Additionally, his research includes a focus on understanding the seismic properties of rocks, especially the influence of fractures, cracks, and ice on seismic velocity and attenuation. His expertise spans applied geophysics, seismic imaging, timelapse seismology, rock physics, geological carbon storage, geothermal energy, and hydrogeophysics.

Selected publications

• Geothermal Reservoir Characterization Using Seismic Moment Tensor Solutions from Distributed Fiber Optic Sensing

  Seismological Research Letters · 2026-02-20 · 1 citations

  articleSenior author

  Abstract Seismic moment tensors provide important information to understand the origin and nature of seismic sources. They have been used to elucidate the dynamics of plate tectonics, the state of active volcanoes, and to characterize subsurface reservoirs. Distributed fiber optic sensing (DFOS) provides unrivaled sampling of the seismic source radiation pattern, which is necessary to estimate moment tensors (MTs). In this study, we demonstrate a significant step toward tapping the potential of moment tensor inversion with DFOS. For that purpose, we analyze more than 14.5 million seismic arrivals to automatically estimate the full MT of thousands of seismic events. The benefits of accessing large numbers of MTs are demonstrated with the characterization of the geothermal reservoir at the Utah Frontier Observatory for Research in Geothermal Energy underground laboratory. The interpretation reveals the important role of the interaction between induced and natural fractures in providing hydraulic connectivity for the enhanced geothermal system at the site. Furthermore, the estimated MTs complement previous studies by providing otherwise inaccessible information about the spatial variability and hydraulic relevance of natural fractures.

  PublisherDOI

• Flow path interpretation from DAS moment tensors applied to the Enhanced Geothermal System at Utah FORGE

  The Leading Edge · 2025-05-21

  articleSenior author

  Abstract We investigate moment tensor solutions of microseismic events observed during the 2023 circulation tests at the Utah Frontier Observatory for Geothermal Research (Utah FORGE). The microseismicity was recorded using two distributed acoustic sensing arrays located in separate wells, one of them the production well. Although the moment tensor inversion is ill-conditioned for most of the observed seismicity, there is a small group of events for which reliable solutions could be estimated. This group can be organized into two event families based on their geometry and style of activation. Furthermore, the two families also show spatial and temporal separations, which permit estimation of the local direction of flow during the circulation tests. Our interpretation suggests that, based on their location and time of activation, the fluid first reached a fracture family located north of the injection well and close to the same depth. Then, this fracture set channeled the fluids, favoring migration in an east-upward direction following their geometrical orientation until reaching the second fracture zone. The geothermal reservoir at Utah FORGE has been described as containing multiple sets of preexisting fracture families with varying orientation, generally not aligned with the current direction of the maximum horizontal stress. Thus, the moment tensor solutions provide important information to identify which fracture families are being stimulated, and significantly, their relationship to interwell flow during Enhanced Geothermal System operations.

  PublisherDOI

• Moment Tensor Inversion of Microseismic Events Using Strain Waveforms Recorded by Multi-Well-Distributed Acoustic Sensing

  Bulletin of the Seismological Society of America · 2025-12-18

  article

  ABSTRACT Distributed acoustic sensing (DAS) array seismic data are now routinely acquired on fiber-optic cables in wells for downhole monitoring of microseismic events during geothermal and oil and gas operations. In an enhanced geothermal system experiment in Blue Mountain, Nevada, downhole DAS arrays operational in three different wells at all times provided unprecedented constraints on the locations and source radiation patterns of the microseismic events. We develop a simple framework for inverting low-frequency (∼4 to 16 Hz) complete axial strain waveforms recorded by DAS for point-source moment tensors using axial strain Green’s functions calculated for a 1D velocity model using frequency–wavenumber integration. We fit the strain waveforms recorded at two to three wells with a variance reduction of ∼36% to 74%. We constrain the best-fitting source types to be strongly deviatoric; assuming a double-couple mechanism, we obtain predominantly normal faulting and right-lateral strike-slip faulting mechanisms on northwest to north-northwest-trending faults that agree with the geologic knowledge of the study area and the extensional Basin and Range tectonics prevalent in Nevada. We further validate magnitudes derived from low-frequency strain spectral amplitudes of far-field body waves by comparing them with magnitudes derived from moment tensors. Finally, for two of the larger events, we find the strike-slip focal mechanisms derived from the DAS data to be consistent with those estimated from low-frequency, vertical-component displacement waveforms recorded by a sparse network of surface seismometers. Moment tensor inversion applied to downhole DAS arrays helps characterize the size of the microseismic events that are relevant to induced seismicity, and the state of stress in the subsurface during geothermal, fracturing, and oil and gas operations. The inversion framework is general, and with a sufficiently accurate velocity model and good signal-to-noise ratio at frequencies lower than the corner frequency, it can be extended to dark fiber DAS arrays at the surface as well.

  PublisherDOI

• Insights Into Seismicity Associated With Flexibly Operating Enhanced Geothermal System From Real‐Time Distributed Acoustic Sensing

  Journal of Geophysical Research Solid Earth · 2025-07-01 · 1 citations

  articleOpen accessCorresponding

  Abstract Enhanced Geothermal Systems (EGS) have the capacity to broaden the accessible resource pool for geothermal power generation. Traditionally viewed as a “baseload” resource, their flexible operation might also enable dispatchable load‐following generation and long‐term energy storage, aligning them with the evolving landscape of decarbonized electricity systems. However, increasing permeability and extracting energy during EGS operations can induce microseismic events; for many prior EGS efforts, some associated seismicity has been observed. While energetically beneficial, the flexibility of EGS operations prompts our inquiry into whether new types of operations will yield previously unseen seismicity patterns. We demonstrate the use of distributed acoustic sensing (DAS) with real‐time edge computing to monitor seismicity during a pilot test of a cyclically operated EGS facility at the Blue Mountain geothermal field. Our focus lies in uncovering seismicity insights from the real‐time microseismic catalog, particularly during load‐following dispatchability tests simulating flexible EGS operation. We find that variations in pore pressure consistently correlate with seismicity, and that controlling pressure cycles during flexible operations appears to constrain microseismic activity during subsequent cycles. The spatio‐temporal evolution of microseismic clouds recorded during cyclic injection cycles fits diffusive models over our available observation period. Additionally, seismicity elevation lags behind pore pressure increases, likely due to pressure diffusion to the fracture system boundary. Through real‐time monitoring, we offer novel insights into seismicity associated with flexibly operating EGS. Our findings suggest that leveraging DAS and edge computing can inform EGS operations and help mitigate induced seismicity.

  PublisherOA PDFDOI

• Flow path interpretation from DAS moment tensors applied to the enhanced geothermal system at Utah FORGE

  The Leading Edge · 2025-10-01 · 1 citations

  articleSenior author

  Abstract We investigate the moment tensor solutions of microseismic events observed during the 2023 circulation tests at the Utah Frontier Observatory for Research in Geothermal Energy (FORGE). The microseismicity was recorded using two distributed acoustic sensing arrays located in separate wells, one being the production well. Although the moment tensor inversion is ill-conditioned for most of the observed seismicity, there is a small group of events for which reliable solutions could be estimated. This group can be organized into two event families based on their geometry and style of activation. The two families also show spatial and temporal separations, which permits estimation of the local direction of flow during the circulation tests. Our interpretation suggests that, based on their location and time of activation, the fluid first reached a fracture family located north of the injection well and close to the same depth. Then, this fracture set channeled the fluids, favoring migration in an east-upward direction following their geometrical orientation until reaching the second fracture zone. The geothermal reservoir at Utah FORGE has been described as containing multiple sets of preexisting fracture families with varying orientation, generally not aligned with the current direction of the maximum horizontal stress. Thus, the moment tensor solutions provide important information to identify which fracture families are being stimulated, and significantly, their relationship to interwell flow during enhanced geothermal system operations.

  PublisherDOI

• Unveiling Cryosphere Dynamics by Distributed Acoustic Sensing and Data‐Driven Hydro‐Thermo Coupled Simulation

  Geophysical Research Letters · 2025-01-27 · 9 citations

  articleOpen accessSenior author

  Abstract As global warming continues, the Earth's cryosphere is experiencing severe degradation. This study leverages a novel combination of distributed acoustic sensing (DAS) and artificial intelligence to monitor and decipher cryospheric dynamics. We have developed an advanced time‐lapse surface wave analysis workflow to capture shear wave velocity changes during a 2‐month controlled permafrost thaw experiment in Fairbanks, Alaska. To understand the underlying physical mechanisms of , multimodal rock‐physics simulations were conducted to associate the observed to hydrological and thermal processes like heating and rainfall events. Furthermore, we employ a physics‐guided deep learning algorithm alongside interpretable techniques to evaluate the impact of various physical factors and shed light on the cryospheric hydro‐thermo coupling mechanisms. This study highlights the potential of using DAS and data‐driven rock‐physics simulation for complex cryosphere monitoring and offers a comprehensive view of the permafrost's thawing dynamics.

  PublisherOA PDFDOI

• Control Mechanisms for Self‐Sealing in Activated Clay‐Rich Faults Through Controlled Hydraulic Injection Experiment

  Water Resources Research · 2025-04-01 · 5 citations

  articleOpen access

  Abstract In a high‐pressure injection fault activation experiment conducted at the Mont Terri underground research laboratory in Switzerland, the transmissivity of the Opalinus Clay fault significantly increased due to opening and shearing. The fluid injection, spanning a few hours, generated a 10 m radius fault activation patch. Subsequent pressure pulse tests conducted bi‐weekly for a year revealed the gradual return of fault transmissivity to its initial state. The study utilized fluid pressure decay analysis, optical fiber monitoring, continuous active source seismic measurements and borehole displacement sensors for measuring fault displacements. The fault zone exhibited a dilation of approximately 1.4 mm, associated with both normal and tangential movements during activation, resulting in a sudden transmissivity increase from 1 × 10 −12 to 3.2 × 10 −7 m 2 /s. Early post‐activation, transient compaction and the subsequent slow compaction were observed, transitioning to an extension regime. The pressure pulse tests demonstrated a rapid transmissivity drop by more than two orders of magnitude within the first 10 days, followed by a gradual and less pronounced decrease. Plastic shear and compaction dominated the transmissivity evolution until 70 days after injection ended, followed by a period where additional factors, such as clay mineral swelling, influenced the behavior. Extrapolation suggested a sealing process taking at least 50 years after the initial activation.

  PublisherDOI

• Active-seismic monitoring of reservoir pressure changes in an analog reservoir

  Geophysics · 2025-10-27

  article

  ABSTRACT Geophysical monitoring of pore pressure within geologic carbon storage (GCS) reservoirs is critical for understanding reservoir containment and caprock integrity. Time-lapse seismic methods are useful for probing reservoir state at locations away from instrumented wells. Highly sensitive and stable time-lapse seismic methods are required for monitoring subtle changes induced by reservoir pressure. To test the limits of time-lapse seismic sensitivity to changes in pore pressure, we used continuous active-source seismic monitoring (CASSM) to monitor traveltime changes caused by pressure perturbations in a laboratory-scale analog reservoir. We referred to this analog reservoir as SMARTT (seismic monitoring of an analog reservoir testing tank), which is a highly instrumented tank filled with sand and bentonite clay to emulate a reservoir, caprock, and aquifer. We injected water directly into the reservoir to mimic the effects of increased pore pressure caused by far-field CO2 injection. We conducted a total of five injections over the course of two days with shut-in periods in between. CASSM successfully acquired data throughout the injections at high sensitivities, such that background changes in P-wave arrival times had an average standard deviation of 82 ns. CASSM was able to capture, at high correlations, changes in P-wave arrival (Δt) caused by changes in reservoir pore pressure (ΔPp). Using a reservoir simulator, we inverted rock property values for the reservoir and caprock layers by modeling the reservoir pressures for the entire experiment. Modeling results showed that caprock permeability evolved during the experiment. We used granular contact theory models to show that these Δt were a result of ΔPp. We used the contact theory models to upscale the stress state and pore-pressure perturbations that would be appropriate for commercial GCS sites to show that pore-pressure monitoring at this scale is feasible. These results suggested that time-lapse seismic methods, such as CASSM, can be used for probing changes in sealing integrity.

  PublisherDOI

• DAS Moment Magnitude Calculation in the Time Domain for General Dislocations: Application at Utah FORGE

  Bulletin of the Seismological Society of America · 2025-09-04 · 1 citations

  articleSenior author

  ABSTRACT We developed a new formulation for the estimation of seismic moment using far-field, time-domain strain measurements from distributed acoustic sensing (DAS). The method takes into account the axial component nature of DAS measurements, thus removing bias related to an incomplete sampling of the strain field. For the implementation, we computed new spherical coefficients that account for the effect of compressional and shear radiation patterns in the distributed strain formulation. For comparison, we also extended the estimation of the spherical averages of displacement radiation patterns to non-double couples. For such a purpose, we apply a general dislocation model, for which pure double couples are a particular instance. We utilize this new formulation to analyze microseismic events observed during the 2023 circulation tests at the Utah FORGE site. We also evaluated different aspects that can bias the magnitude estimations, including background noise, the sampling of the focal sphere provided by borehole DAS arrays, and the assumption of pure double-couple source mechanisms. In addition, we also compared the DAS estimations with independent results obtained with a seismometer and from the moment tensor inversion of the DAS records. Our analysis shows consistency between different magnitude estimation approaches when various biasing factors are taken into consideration.

  PublisherDOI

• Source mechanism of kHz microseismic events recorded in multiple boreholes at the first EGS Collab testbed

  Geothermics · 2024-03-19 · 7 citations

  articleOpen access

  Continuous microseismic monitoring using three-component (3C) accelerometers deployed in multiple boreholes allows for tracking the detailed evaluation of mesoscale (∼10 m scale) fracture growth during the fracture stimulation experiments at the first Enhanced Geothermal Systems (EGS) Collab testbed. Building on a well-constrained microseismic event catalog, we invert for moment tensor of the events to better understand the fracture geometry and stress orientations. However, it is challenging because of the unknown orientation of 3C accelerometers and low signal-to-noise-ratio nature of high-frequency (several kHz) monitoring. To address these challenges, we first perform the hodogram analysis on the continuous active-source seismic monitoring (CASSM) data to determine the orientations of the 18 3C accelerometers. We then apply the principal component analysis (PCA) to the observed microseismic waveforms to improve the signal-to-noise ratios. We perform a grid search for the full moment tensor by fitting the PCA-denoised waveforms at a frequency range of 5 to 8 kHz. The moment tensor results show both the creation of hydraulic fractures and the reactivation of natural fractures during the hydraulic stimulations. Our stress inversion based on the inverted moment tensors reveals the alteration of stress regime caused by hydraulic fracture stimulations.

  PublisherDOI