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Objective On February 6, 2023, double strong earthquakes of MW7.8 and MW7.5 occurred consecutively within 10 hours in the Kahramanmaraş province in central-southern Turkey. After these double-strong earthquakes, domestic and foreign seismologists studied coseismic surface deformation using field measurements, GNSS, and differential InSAR methods. However, owing to the limitations in the techniques employed, the current coseismic surface deformation results suffer from low spatial resolution and missing data near fault surface ruptures. This study aims to address these limitations and comprehensively present the coseismic surface deformation of the double earthquakes in Turkey. Methods Using Sentinel-2 optical image data, the east-west and north-south surface coseismic deformation fields of Turkey' s double-strong earthquakes were obtained using the image correlation method, and these surface deformations were converted into sinistral strike-slip displacement along the fault direction. Results The deformation field results showed that the surface rupture lengths of the double earthquakes are approximately 280 and 130 km, respectively. The average strike-slip displacement of the first MW7.8 earthquake is 4.2±1.66 m; the maximum strike-slip displacement is 6.9±0.81 m. The average strike-slip displacement of the subsequent MW7.5 earthquake is 4.9±2.45 m, and the maximum strike-slip displacement is 9.6±1.16 m. Conclusion Comparison of the horizontal displacement results obtained using the COSI-Corr method and field measurements revealed that the maximum horizontal displacements obtained using the two methods are consistent. In contrast, the average displacement results obtained using the COSI-Corr method are slightly larger than the horizontal displacement results obtained using field measurements, attributed to the inclusion of "off-fault" deformations. Significance This study not only provides deformation data and constraints for the fault-slip inversion model but also deepens the understanding of factors controlling the rupture behavior of strike-slip faults.

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Objectives: Co-seismic deformation monitoring is of great significance for the interpretation of co-seismic deformation characteristics and intuitive understanding of fault geometric characteristics. For large earthquakes with surface rupture, global navigation satellite system(GNSS) technique has a low spatial resolution, and interferometric synthetic aperture radar(InSAR) technology will cause phase decorrelation due to large deformation gradients, it is impossible to obtain specific deformation around the fault. Optical image correlation(OIC) and pixel offset tracking(POT) based on sub-pixel cross-correlation can solve these problems well. Methods: The main idea of the sub-pixel cross-correlation method is to use the pre-event image in the two images as a reference, and then compare the post-event image with it to evaluate the similarity between the two images, and then retrieve the displacement between the homonymous points. OIC can obtain east-west and north-south deformations, and POT can obtain range and azimuth deformations. In this paper, the deformation in each direction of the Kaikoura earthquake obtained from Sentinel-1 data and Sentinel-2 data is used to form different combinations, and the least square method is used to calculate the three-dimensional deformation. Results: The combination of OIC+POT_As_Des has the best constraint. The accuracy of the north-south deformation obtained by OIC+POT_Range is not as good as that of OIC+POT_As_Des. Compared with POT_As_Des, the north-south deformation precision obtained by it is higher, and the deformation performance on the right side of the Kekerengu fault and the left side of the Papatea fault is also better. In the northeast of the Kaikoura earthquake epicenter, very complex and huge surface deformation and multiple ruptures were detected in two close areas, and the vertical defoamation was mainly uplift. Conclusions: For Sentinel-1 and Sentinel-2, the combination of OIC+ POT_As_Des is most suitable for obtaining the three-dimensional deformation of the Kaikoura earthquake. This earthquake is a dextral strike-slip earthquake with reverse. [ABSTRACT FROM AUTHOR]

In February 2023, Mw 7.8 and Mw 7.7 earthquakes struck southeastern Turkey. Generating a coseismic 3D deformation field that can directly reflect the characteristics of surface deformation is important for revealing the movement mode of a seismogenic fault and analyzing the focal mechanism. Optical image sub-pixel correlation (SPC) only captures deformation in the horizontal direction, and SAR image pixel offset tracking (POT) obtains range deformation that is not sensitive to north–south deformation signals. Thus, neither of them can capture the complete 3D deformation alone. Combining them may be able to allow the monitoring of 3D deformation. In this study, we used Sentinel-2 optical images to obtain the horizontal deformation (east–west and north–south) and Sentinel-1 and ALOS-2 data to extract the range and azimuth offsets. The least-squares method was used to fuse the optical and SAR offsets to obtain the 3D deformation field of the 2023 Turkey earthquake sequence, which indicates that the two events were both left-lateral strike-slip earthquakes. The surface deformation caused by the two large earthquakes is mainly in the east–west direction. In the vertical direction, the two earthquakes caused a small-magnitude uplift and subsidence. The findings in this paper can be used as a reference for the study of coseismic 3D deformation. [ABSTRACT FROM AUTHOR]

The shallow 1971 MW 6.6 San Fernando, California earthquake involved a complex rupture process on an immature thrust fault with a non‐planar geometry, and is notable for having a higher component of left‐lateral surface slip than expected from seismic source models. We extract its 3‐D coseismic surface displacement field from aerial stereo photographs and document the amount and width of the vertical and fault trace‐parallel components of distributed deformation along strike. The results confirm the significant left‐lateral surface offsets, suggesting a slip vector rotation at shallow depths. Comparing our offsets against field measurements of fault slip, we observe that most of the offset was accommodated in the damage zone, with off‐fault deformation averaging 69% in both the fault trace‐parallel and vertical components. However, the magnitude and width of off‐fault deformation behave differently between the vertical and fault trace‐parallel components, which, along with the rotation in rake near the surface, can be explained by dynamic rupture effects. Plain Language Summary: The 1971 San Fernando, California earthquake is infamous for its strong ground motions and large lateral fault offsets measured in the field, despite the compressional tectonic stresses that triggered the earthquake. We produce maps of the 3‐D surface deformation that occurred during the earthquake by comparing pre‐earthquake and post‐earthquake aerial photographs of this area. The results confirm the presence of important lateral and compression‐driven deformation at the surface. This surface deformation was distributed over a wide zone, and as such, previously reported field measurements did not capture the total slip that occurred at the surface. Understanding controls on the width of the deformation zone provides insight into earthquake behavior and helps improve our estimates of seismic hazard. Our results show that during the San Fernando earthquake, lateral and compression‐driven deformation behaved differently within the fault zone, which may suggest that the two slip components were affected by different factors and damage generation mechanisms. Key Points: Correlation of aerial photographs reveals significant left‐lateral surface deformation in the 1971 San Fernando earthquakeOff‐fault deformation is partitioned between the fault trace‐parallel and vertical components of deformationPrimary controls of off‐fault deformation may be different for the fault trace‐parallel and vertical components [ABSTRACT FROM AUTHOR]

In February 2023, Mw 7.8 and Mw 7.7 earthquakes struck southeastern Turkey. Generating a coseismic 3D deformation field that can directly reflect the characteristics of surface deformation is important for revealing the movement mode of a seismogenic fault and analyzing the focal mechanism. Optical image sub-pixel correlation (SPC) only captures deformation in the horizontal direction, and SAR image pixel offset tracking (POT) obtains range deformation that is not sensitive to north–south deformation signals. Thus, neither of them can capture the complete 3D deformation alone. Combining them may be able to allow the monitoring of 3D deformation. In this study, we used Sentinel-2 optical images to obtain the horizontal deformation (east–west and north–south) and Sentinel-1 and ALOS-2 data to extract the range and azimuth offsets. The least-squares method was used to fuse the optical and SAR offsets to obtain the 3D deformation field of the 2023 Turkey earthquake sequence, which indicates that the two events were both left-lateral strike-slip earthquakes. The surface deformation caused by the two large earthquakes is mainly in the east–west direction. In the vertical direction, the two earthquakes caused a small-magnitude uplift and subsidence. The findings in this paper can be used as a reference for the study of coseismic 3D deformation.

We generated dense, high‐resolution 3‐D ground displacement maps for the 2016 MW 7.8 Kaikōura, New Zealand earthquake—the most geometrically and kinematically complex rupture yet recorded—from stereo WorldView optical satellite imagery using a new methodology that combines subpixel image correlation with a ray‐tracing approach. Our analysis reveals fundamental new details of near‐field displacement patterns, which cannot easily be obtained through other methods. From our detailed correlation maps, we measured fault slip in 3‐D along 19 faults at 500‐m spacing. Minimum resolvable horizontal slip is ~0.1 m, and vertical is ~0.5 m. Net slip measurements range from <1 to ~12 m. System‐level kinematic analysis shows that slip on faults north of the Hope fault was oriented primarily subparallel to the Pacific‐Australian plate motion direction. In contrast, slip on faults to the south was primarily at high angle to the plate motion and secondarily parallel to plate motion. Fault kinematics are in some locations consistent with long‐term uplift patterns, but inconsistent in others. Deformation within the Seaward Kaikōura Range may indicate an attempt by the plate boundary fault system to geometrically simplify. Comparison of published field measurements along the Kekerengu fault with our correlation‐derived measurements reveals that ~36% of surface displacement was accommodated as distributed off‐fault deformation when considering only field measurements of discrete slip. Comparatively, field measurements that project previously linear features (e.g., fence lines) into the fault over apertures >5–100 m capture nearly all (~90%) of the surface deformation. Key Points: Correlation of high‐resolution optical satellite imagery reveals 3‐D surface deformation patterns of the 2016 MW 7.8 Kaikōura earthquakeKinematic analysis shows slip on northern faults was subparallel to plate motion but slip on southern faults was transpressionalComparison of Kekerengu fault field measurements with image correlation measurements reveals up to ~36% distributed deformation [ABSTRACT FROM AUTHOR]

• The fault structure is acquired very early in its history. • The fault structure is controlled by the Riedels and the width of diffuse zone. • Off-fault deformation is localized in the relay zones and along the old shear bands. • Fault zone width and OFD ratio decrease with displacement, to reach a stable value. • Explains why uplift is a good marker of off-fault deformation zones. Surface deformation associated with strike-slip faults can be distributed in space, with deformation located either along the primary fault strand or around it and referred to as off-fault deformation (OFD). Fault displacement hazard evaluation require to identify and estimate surface slip rates along active fault strands. We calculate the horizontal and vertical displacement of the analogue models surfaces with optical image correlation and photogrammetry, to investigate the OFD's development with increasing cumulative deformation. The criterion uses the gradient of the horizontal displacement norm perpendicular to the basal fault. Below 0.005 (noise level), there is no deformation, up to 0.03, it is off-fault-deformation, above 0.03, it is on-fault. We confirm previous observations made on analogue models that the surface deformation starts with a broad diffuse deformation, then produces fault strands alternating with relay zones that may be abandoned and reactivated. OFD is located first between Riedels, then between synthetic shears, and finally takes place in the relay zones. We also show that the OFD initially accommodates 100% of the applied slip (no faults), then decreases abruptly during the Riedels stage down to 20 to 30% to finally remain stable for the rest of the experiment. The abandonment and reactivation of the relay zones has the consequence of maintaining the OFD ratio on a stable value. Our experiments show that, like the OFD ratio, the width of the fault zone decreases with cumulative displacement to reach a stable value. Consequently, the OFD is correlated with this fault zone width and its geometric complexities. The ratios of OFD observed in this study are also consistent with measurements of OFD made on seven natural faults that exhibit different cumulative displacements. Hence our models suggest that strike-slip faults will never reach a continuous, linear geometry, and will always maintain a minimum amount of OFD. [ABSTRACT FROM AUTHOR]