Oceanic transform faults display a unique combination of seismic and aseismic slip behavior, including a large globally averaged seismic deficit, and the local occurrence of repeating magnitude (M)
Ocean transform faults often generate characteristic earthquakes that repeatedly rupture the same fault patches. The westernmost Gofar transform fault quasi‐periodically hosts ∼
- PAR ID:
- 10401673
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Solid Earth
- Volume:
- 128
- Issue:
- 3
- ISSN:
- 2169-9313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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earthquakes with abundant foreshocks and seismic swarms, as on the Gofar transform of the East Pacific Rise and the Blanco Ridge in the northeast Pacific Ocean. However, the underlying mechanisms that govern the partitioning between seismic and aseismic slip and their interaction remain unclear. Here we present a numerical modeling study of earthquake sequences and aseismic transient slip on oceanic transform faults. In the model, strong dilatancy strengthening, supported by seismic imaging that indicates enhanced fluid-filled porosity and possible hydrothermal circulation down to the brittle–ductile transition, effectively stabilizes along-strike seismic rupture propagation and results in rupture barriers where aseismic transients arise episodically. The modeled slow slip migrates along the barrier zones at speeds 10 to 600 m/h, spatiotemporally correlated with the observed migration of seismic swarms on the Gofar transform. Our model thus suggests the possible prevalence of episodic aseismic transients in M rupture barrier zones that host active swarms on oceanic transform faults and provides candidates for future seafloor geodesy experiments to verify the relation between aseismic fault slip, earthquake swarms, and fault zone hydromechanical properties. -
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Abstract To better quantify how injection, prior seismicity, and fault properties control rupture growth and propagation of induced earthquakes, we perform a finite‐fault slip inversion on a
M w4.0 earthquake that occurred in April 2015, the largest earthquake in an induced sequence near Guthrie, Oklahoma. The slip inversion reveals a rupture with slip patches that are anti‐correlated to the locations of prior seismicity. The prior seismicity driven by low pore pressure changes and static stress changes occurred on weaker portions of the fault, while theM w4.0 earthquake likely ruptured relatively stronger portions of the fault. To resolve if pore pressure changes or the initial underlying stress distribution and fault strength controlled the final slip distribution of the GuthrieM w4.0 earthquake, we compare strike‐slip events of similar magnitude from tectonically active regions and previously inactive regions. Earthquakes on reactivated faults exhibit different slip distributions than active regions, they have more prominent and well separated slip patches, a behavior often associated with faults of lower fault maturity. Pore pressure shows little effect on the distributions. These observations suggest that the initial underlying stress distribution and fault strength of reactivated faults in low deformation regions is the primary controlling factor of the slip distribution with pore pressure perturbations and earthquake interactions being secondary. Therefore, GuthrieM w4.0 earthquakes slip distribution was enhanced by pore‐pressure perturbations and earthquake interactions by creating an optimal stress state for its failure, but the slip distribution itself is controlled by its fault's initial stress and strength state. -
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Abstract Oceanic transform faults connect spreading centers and are imprinted with previous tectonic events. However, their tectonic interactions are not well understood due to limited observations. The Discovery transform fault system at 4°S, East Pacific Rise (EPR), represents a young transform system, offering a unique opportunity to study the interplay between faulting and other tectonic events at an early phases of an oceanic transform system. Discovery regularly hosts
M 5–6 characteristic earthquakes, and the seafloor north of Discovery includes a 35 km‐long rift zone that records a complex history of rifting, faulting and volcanism, suggesting that the transform faults likely interact with regional tectonic activity. We apply a machine‐learning enabled workflow to locate 21,391 earthquakes recorded during a 1‐year ocean bottom seismometer experiment in 2008. Our results indicate that seismicity on the western Discovery fault is separated into seven patches with distinct aseismic and seismic slip modes. Additionally, we observe a patch of off‐fault seismicity near where seafloor abyssal hills intersect the rift zone. This seismicity may have been caused by varying opening rates as spreading rate decreases from north to south in the rift zone. Our findings suggest that the Discovery system is still evolving, and that system equilibrium has not been reached between rifting and faulting. These results reflect the complex yet rarely observed interactions between fault slip, plate rotation, and rifting which are likely ubiquitous at oceanic transform systems. -
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Abstract Two major earthquakes (MW7.8 and MW7.7) 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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Abstract The 1938
M S 8.3 and 2021M W 8.2 earthquakes both ruptured within the Semidi segment of the Aleutian‐Alaska subduction zone. The large‐slip distribution of the 2021 event is well constrained within the depth range 25–45 km, with seaward tsunami observations excluding significant shallower coseismic slip. The 1938 event slip distribution is more uncertain. Regional and far‐field tide gauge observations for the 1938 event are modeled to constrain the location of large coseismic slip. The largest slip (2.0 m) is located below the continental shelf on a 180‐km‐long portion of the rupture extending further northeast than the 2021 rupture, to near Sitkinak Island. Minor slip (1.0 m) extends seaward under the continental slope to 8 km deep, where large slip may have occurred in 1788. The megathrust shallower than 25 km depth to the southwest experienced many small aftershocks and aseismic slip following the 2021 event, and has limited slip deficit.
