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1. Rupture Process of the 2019 Ridgecrest, California Mw 6.4 Foreshock and Mw 7.1 Earthquake Constrained by Seismic and Geodetic Data

   https://doi.org/10.1785/0120200108  

   Wang, Kang; Dreger, Douglas S.; Tinti, Elisa; Bürgmann, Roland; Taira, Taka’aki (July 2020, Bulletin of the Seismological Society of America)

   null (Ed.)

   ABSTRACT The 2019 Ridgecrest earthquake sequence culminated in the largest seismic event in California since the 1999 Mw 7.1 Hector Mine earthquake. Here, we combine geodetic and seismic data to study the rupture process of both the 4 July Mw 6.4 foreshock and the 6 July Mw 7.1 mainshock. The results show that the Mw 6.4 foreshock rupture started on a northwest-striking right-lateral fault, and then continued on a southwest-striking fault with mainly left-lateral slip. Although most moment release during the Mw 6.4 foreshock was along the southwest-striking fault, slip on the northwest-striking fault seems to have played a more important role in triggering the Mw 7.1 mainshock that happened ∼34  hr later. Rupture of the Mw 7.1 mainshock was characterized by dominantly right-lateral slip on a series of overall northwest-striking fault strands, including the one that had already been activated during the nucleation of the Mw 6.4 foreshock. The maximum slip of the 2019 Ridgecrest earthquake was ∼5  m, located at a depth range of 3–8 km near the Mw 7.1 epicenter, corresponding to a shallow slip deficit of ∼20%–30%. Both the foreshock and mainshock had a relatively low-rupture velocity of ∼2  km/s, which is possibly related to the geometric complexity and immaturity of the eastern California shear zone faults. The 2019 Ridgecrest earthquake produced significant stress perturbations on nearby fault networks, especially along the Garlock fault segment immediately southwest of the 2019 Ridgecrest rupture, in which the coulomb stress increase was up to ∼0.5  MPa. Despite the good coverage of both geodetic and seismic observations, published coseismic slip models of the 2019 Ridgecrest earthquake sequence show large variations, which highlight the uncertainty of routinely performed earthquake rupture inversions and their interpretation for underlying rupture processes. 

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2. Complex multi-fault rupture and triggering during the 2023 earthquake doublet in southeastern Türkiye

   https://doi.org/10.1038/s41467-023-41404-5  

   Liu, Chengli; Lay, Thorne; Wang, Rongjiang; Taymaz, Tuncay; Xie, Zujun; Xiong, Xiong; Irmak, Tahir Serkan; Kahraman, Metin; Erman, Ceyhun (December 2023, Nature Communications)

   Abstract Two major earthquakes (M_W7.8 and M_W7.7) ruptured left-lateral strike-slip faults of the East Anatolian Fault Zone (EAFZ) on February 6, 2023, causing >59,000 fatalities and ~$119B in damage in southeastern Türkiye and northwestern Syria. Here we derived kinematic rupture models for the two events by inverting extensive seismic and geodetic observations using complex 5-6 segment fault models constrained by satellite observations and relocated aftershocks. The larger event nucleated on a splay fault, and then propagated bilaterally ~350 km along the main EAFZ strand. The rupture speed varied from 2.5-4.5 km/s, and peak slip was ~8.1 m. 9-h later, the second event ruptured ~160 km along the curved northern EAFZ strand, with early bilateral supershear rupture velocity (>4 km/s) followed by a slower rupture speed (~3 km/s). Coulomb Failure stress increase imparted by the first event indicates plausible triggering of the doublet aftershock, along with loading of neighboring faults. 

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3. Seismic and Geodetic Analysis of Rupture Characteristics of the 2020 Mw 6.5 Monte Cristo Range, Nevada, Earthquake

   https://doi.org/10.1785/0120200327  

   Liu, Chengli; Lay, Thorne; Pollitz, Fred F.; Xu, Jiao; Xiong, Xiong (July 2021, Bulletin of the Seismological Society of America)

   ABSTRACT The largest earthquake since 1954 to strike the state of Nevada, United States, ruptured on 15 May 2020 along the Monte Cristo range of west-central Nevada. The Mw 6.5 event involved predominantly left-lateral strike-slip faulting with minor normal components on three aligned east–west-trending faults that vary in strike by 23°. The kinematic rupture process is determined by joint inversion of Global Navigation Satellite Systems displacements, Interferometric Synthetic Aperture Radar (InSAR) data, regional strong motions, and teleseismic P and SH waves, with the three-fault geometry being constrained by InSAR surface deformation observations, surface ruptures, and relocated aftershock distributions. The average rupture velocity is 1.5  km/s, with a peak slip of ∼1.6  m and a ∼20  s rupture duration. The seismic moment is 6.9×1018  N·m. Complex surface deformation is observed near the fault junction, with a deep near-vertical fault and a southeast-dipping fault at shallow depth on the western segment, along which normal-faulting aftershocks are observed. There is a shallow slip deficit in the Nevada ruptures, probably due to the immature fault system. The causative faults had not been previously identified and are located near the transition from the Walker Lane belt to the Basin and Range province. The east–west geometry of the system is consistent with the eastward extension of the Mina Deflection of the Walker Lane north of the White Mountains. 

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4. Afterslip and Triggered Slip Following the 6 Feb 2023 Kahramanmaraş Earthquake Sequence, East Anatolian Fault, Türkiye

   https://doi.org/10.1007/978-3-031-87558-8_84  

   Bilham, Roger; Ayruk, Efe Turan; Turğut, Muhammed; İrgüren, Recep; Köküm, Mehmet; Elhisso, Abdulrahman; Farımaz, İlay; Doğan, Uğur (January 2025, Springer Nature Switzerland)

   The Mw7.8 and Mw7.6 Kahramanmaraş earthquakes of 6 Feb 2023 in SW Türkiye resulted in more 10 than 500 km of surface rupture with surface offsets locally exceeding 5 m. The earthquakes induced 5 mm of 11 triggered slip on the North Anatolian Fault at Ismetpasa, but only 1 mm of slip on the East Anatolian Fault at 12 Sivrice. The amplitude of both triggered slip events corresponds to the release a local creep slip-deficit that 13 had developed prior to the earthquakes. In March we installed ten carbon-rod extensometers across segments 14 of these faults to investigate whether surface-slip continues. Of these, seven recorded less than a few mm of 15 slip in the 6 months since the mainshocks revealing that the fault in these locations was now locked. The 16 remaining instruments identified two segments where fault slip continues. At Goksun near the northwestern 17 end of the Mw 7.6 rupture we recorded surface slip preceding local aftershocks, including a unique record of 18 accelerating slip preceding a local Mw4.7 aftershock. A second region of continued slip is found at the eastern 19 end of the Mw 7.8 rupture known as the Puturge gap, a segment of the fault that also arrested coseismic slip in 20 the Elazığ-Sivrice 2020 Mw 6.8 earthquake. The array of five extensometers installed here, including one 52 m 21 long, reveals >3.8 mm/yr of slip to be continuing at depth. In September, creepmeters 45 km apart recorded 22 what appears to be an eastward propagating creep event in the subsurface. To investigate the evolution of 23 subsurface slip here the five creepmeters have been supplemented with a 3-component 1-km-scale cGPS array 24 recording at 5Hz. 

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5. Rupture segmentation on the East Anatolian fault (Turkey) controlled by along-strike variations in long-term slip rates in a structurally complex fault system

   https://doi.org/10.1130/G52403.1  

   Wang, Binhao; Barbot, Sylvain (July 2024, Geology)

   The East Anatolian fault in Turkey exhibits along-strike rupture segmentation, typically resulting in earthquakes with moment magnitude (Mw) up to 7.5 that are confined to individual segments. However, on 6 February 2023, a catastrophic Mw 7.8 earthquake struck near Kahramanmaraş (southeastern Turkey), defying previous expectations by rupturing multiple segments spanning over 300 km and overcoming multiple geometric complexities. We explore the mechanics of successive single- and multi-segment ruptures using numerical models of the seismic cycle calibrated to historical earthquake records and geodetic observations of the 2023 doublet. Our model successfully reproduces the observed historical rupture segmentation and the rare occurrence of multi-segment earthquakes. The segmentation pattern is influenced by variations in long-term slip rate along strike across the kinematically complex fault network between the Arabian and Anatolian plates. Our physics-based seismic cycle simulations shed light on the long-term variability of earthquake size that shapes seismic hazards. 

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