Conference Agenda

Slow-slip events (SSEs) represent a unique form of fault displacement, occurring over days to months rather than the seconds typical of earthquakes. While most commonly observed near tectonic plate boundaries, these events also present hazards in intraplate regions, particularly where underground infrastructure, such as production and saltwater disposal (SWD) wells, intersect fault zones. Unlike seismic events, SSEs are typically aseismic and can only be detected through geodetic measurements, making them a silent but significant risk to subsurface and surface operations.

Between March 2022 and January 2023, a slow-slip event was detected in Howard County, in the Midland Basin, using Interferometric Synthetic Aperture Radar (InSAR) data processed through the Small Baseline Subset (SBAS) technique. This geodetic monitoring revealed surface deformation patterns indicative of fault activity that would otherwise have remained undetected. The region is known for extensive saltwater disposal operations, integral to oil and gas production, making accurate fault characterization crucial for risk management.

The deformation velocity maps generated during this period were used to estimate fault parameters, including location, geometry, and slip kinematics, through Bayesian source inversion. This method provided probabilistic insights into the fault’s behavior, enhancing the reliability of the interpretations. The inversion results indicated a shallow, low-angle normal fault striking perpendicular to the geographically widespread Grenville thrust front that has released the equivalent energy to an earthquake with a moment magnitude of ~5.3. The SSE fault orientation and geometry align closely with secondary orthogonal seismogenic zones identified in 2D regional reflection seismic lines, reinforcing the validity of the geodetic analysis and seismic correlation.

Interestingly, the slow-slip event was temporally preceded by a seismic swarm located at the northern edge of the identified fault plane. This correlation suggests a potential interaction between seismic and aseismic faulting processes. The seismic swarm may have induced stress changes that triggered the subsequent slow-slip event, offering new perspectives on fault dynamics in intraplate settings.

These observations have practical implications for regional risk management. Saltwater disposal wells, essential for handling wastewater from oil and gas extraction, greatly increase pore pressure and affect areas that are particularly vulnerable to fault slip, which can compromise well integrity. Critically stressed faults might slip even under minor perturbations as might be imposed by saltwater disposal. By incorporating surface deformation patterns indicative of fault activity, operators can implement proactive measures, such as adjusting injection rates and relocating SWD wells, to mitigate the risk of damage to health, safety and the environment.

This study underscores the critical role of geodetic monitoring, particularly InSAR, in detecting and analyzing slow-slip events in active oil-producing basins. The integration of advanced techniques like Bayesian fault inversion allows for more precise fault characterization, improving our understanding of fault systems and their potential impacts. As oil and gas activities expand in regions like the Permian Basin, incorporating geodetic surveillance into routine monitoring will be essential for minimizing geohazard risks and ensuring the safety of underground infrastructure and operations.

The Howard County SSE case demonstrates the value of combining wide-area InSAR data with subsurface data to enhance hazard assessment and infrastructure protection, setting a precedent for future monitoring efforts in oil-producing regions.

Our understanding of the kinematics, dynamics, and seismic potential of tectonically active continental interiors remains a long-standing challenge, particularly in structurally complex and earthquake-prone regions such as the Tianshan orogen. Large-scale, high-resolution mapping of surface velocities and strain rates from satellite geodesy offers a powerful perspective for addressing these issues.

Here, we utilize approximately 10 years (2014–2024) of Sentinel-1 SAR imagery together with data from ~1,000 GNSS stations to derive average surface velocities and horizontal strain rates across ~2 million square kilometers in and around the Tianshan at 500 m spatial resolution. The results reveal pronounced lateral variations in present-day Tianshan deformation. Strain and deformation are strongly concentrated in the southwestern segment, particularly within the Pamir–Tianshan convergence zone, along the Talas–Fergana Fault, and across the Kashi and Keping fold-and-thrust belts, whereas other regions are characterized predominantly by more distributed deformation. Overall, the Tianshan accommodates ~20 mm/yr of north–south shortening and ~5 mm/yr of east–west extension.

Based on the derived surface velocities and strain rates, we first assess the seismic potential of the Tianshan. Using geodetically constrained surface strain rates within an elastic half-space framework, we model 97 major faults (439 segments) to invert for slip-deficit rates—an indicator of the rate at which elastic strain energy is accumulating on these faults. By integrating historical seismicity, we further quantify the regional seismic moment budget and identify fault segments capable of generating Mw ≥ 7.0 earthquakes.

We further investigate the deeper lithospheric dynamics underlying the observed deformation. Constrained by surface velocities, we approximate the Tianshan and surrounding regions using a 2D faulted viscous continuum model that allows for lateral variations in lithospheric strength as well as displacement along major faults. The results highlight strong contrasts in lithospheric strength between the Tianshan–Pamir region and adjacent blocks, including the Tarim Basin, Junggar Basin, and Kazakh Platform, as well as moderate lateral variations in effective lithospheric viscosity within the Tianshan itself. Our modeling suggests that far-field boundary stresses associated with the India–Eurasia collision dominate the present-day deformation of the Tianshan, outweighing internal buoyancy forces related to gravitational potential energy gradients.

Together, these results demonstrate that high-resolution geodetic velocity and strain rate fields provides critical insights into continental deformation processes and associated seismic hazards.

The 29th July, 2025 M8.8 Kamchatka earthquake was one of the ten largest earthquakes in instrumental history. It occurred along a portion of the southern shore of the Kamchatka peninsula where pre-event GNSS velocities had indicated a high likelihood of frictional locking of the Kamchatka megathrust. The estimated source location overlaps in space with the source region of the 1952 M9.0 great Kamchatka earthquake, however there were significant differences between the two events – notably in the sizes of the tsunamis, with the 1952 tsunami having significantly greater far-field runup (up to 6 m) across most of the Pacific basin than that of the 2025 event (up to 2.5 m)..

We use InSAR data from multiple tracks (five ascending, three descending) of the Sentinel-1 mission to investigate the deformation of the 2025 earthquake. Using the ISCE2 software to process the data, we employ ionospheric corrections and GACOS troposphere corrections to reduce noise, and obtain good correlation across the peninsula despite the forested terrain. We resolve up to ~1.2 m of line-of-sight displacement, peaking along the SE peninsula shore. In addition, we identify a change in the orientation of the fringes on the northeastern Kuril Islands that constrain the likely westward terminus of rupture. Superimposed on this earthquake deformation field are multiple volcanic deformation signals across the peninsula and islands, apparently stimulated by the earthquake. The largest of these is a dyke intrusion under Krasheninnikov Volcano, around ~230 km north of the mainshock hypocenter, starting two days after the mainshock, that is precursory to that volcano's eruption on 2nd August.

We use quadtree decomposition to downsample our InSAR data, and invert them for coseismic slip on a triangulated mesh of the megathrust, using our models of interseismic locking as a constraint on rupture area, and the plate motion direction as a constraint on rake. Models of uniform slip on our estimated locked area, or of slip limited to the ~5.8 m of slip deficit that should have accumulated since 1952, do not fit the data well. Instead, we find that we can reproduce our InSAR displacements with up to 12 m of slip, divided into two asperities, and modest (< 4 m) trenchward slip, consistent with the modest tsunami for the event. Our estimated moment-magnitude of 8.82 agrees well with seismic estimates.

We note that: 1) tsunami inversions of the 1952 event require greater shallow slip than our model shows, suggesting that the 2025 event was not a repeat of 1952; and 2) the amount of peak slip is over double the slip deficit that likely accrued since 1952, given the 80 mm/yr convergence accommodated by the megathrust, implying that some of the slip deficit that accumulated prior to 1952 was instead released in 2025. Thus, despite the Kamchatka megathrust hosting two of the ten largest earthquakes in the instrumental record, we argue that both of these events were partial ruptures – i.e. neither of them is likely to have been the "big one" for the region. Rather, an event in 1737, with reported run up of over 15 m in the Aleutian Islands, is likely the last full rupture of the Kamchatka megathrust.

InSAR has been one of the principal tools for monitoring Earth’s surface deformation for more than three decades, supporting geodetic and geophysical investigations ranging from tectonic processes and earthquake mechanics to glacier dynamics and landslides. However, due to its near-polar orbit and side-looking acquisition geometry, conventional InSAR measurements are primarily sensitive to the east–west and vertical components of motion and have limited sensitivity to the north–south component ​(Wright et al., 2004)​. Consequently, accurate three-dimensional (3D) deformation retrieval typically relies on well-distributed GNSS observations or assumes that the north–south component is negligible when deformation is dominated by east–west or vertical motion.

The burst overlap regions inherent to Sentinel-1 TOPS acquisitions provide an opportunity to extract azimuth displacement information and partially resolve the north–south deformation component from spaceborne SAR data. Exploiting burst overlaps within a swath (Burst Overlap Interferometry, or BOI) has been demonstrated as an effective method to improve sensitivity to along-track motion and to outperform conventional offset-tracking approaches in terms of precision​ (Grandin et al., 2016; Prats-Iraola et al., 2012)​. This can be extended by exploiting subswath overlap too (SBOI,​ Nergizci et al. 2025) but standard Sentinel-1SAR focussing still restricts SBOI coverage to approximately 10% of the full Sentinel-1 frame, limiting its spatial continuity and applicability to large rupture zones.

IIn this study, we implement an Extended Subswath and Burst Overlap Interferogram (ESBOI) approach that expands the usable overlap regions by extending the Doppler spectrum used when focussing each burst. This strategy enlarges the effective coverage, albeit with increased phase noise. By increasing the spatial extent of overlap-derived interferograms, ESBOI greatly enhances coverage of north–south displacement measurements to more than 50% of a frame, and improves integration with line-of-sight and offset-derived products for 3D deformation reconstruction.

We apply the ESBOI methodology to two major strike-slip earthquake sequences characterized by exceptionally large north–south displacements: the 2023 Kahramanmaraş doublet (Mw 7.8 and Mw 7.5) and the 2025 Myanmar earthquake (Mw 7.7). These events produced some of the largest north–south surface offsets observed in the geodetic era, locally exceeding 4 meters. These earthquakes provide ideal test cases to evaluate the ability of ESBOI to resolve large along-track deformation gradients in near-field regions, where conventional InSAR coherence is degraded, and to assess its contribution to improving our understanding of where fault slip occurred.

​​Grandin, R., Klein, E., Métois, M., & Vigny, C. (2016). Three-dimensional displacement field of the 2015 Mw8.3 Illapel earthquake (Chile) from across- and along-track Sentinel-1 TOPS interferometry. Geophysical Research Letters, 43(6), 2552–2561. https://doi.org/10.1002/2016GL067954

​Nergizci, M., Lazecky, M., Wright, T. J., Hooper, A., Ou, Q., Magnard, C., & Çakir, Z. (2025). Refining 3D Displacement Fields and Coseismic Slip Models of the 2023 Kahramanmaraş Earthquakes Using Subswath and Burst Overlap Interferometry (SBOI). Journal of Geophysical Research.

​Prats-Iraola, P., Scheiber, R., Marotti, L., Wollstadt, S., & Reigber, A. (2012). TOPS Interferometry With TerraSAR-X. IEEE Transactions on Geoscience and Remote Sensing, 50(8), 3179–3188. https://doi.org/10.1109/TGRS.2011.2178247

​Wright, T. J., Parsons, B. E., & Lu, Z. (2004). Toward mapping surface deformation in three dimensions using InSAR. Geophysical Research Letters, 31(1). https://doi.org/10.1029/2003GL018827

​