Seismicity of oceanic and continental rifts—a geodynamic approach

Sobolev, P. O.; Rundquist, D. V.

doi:10.1016/s0031-9201(98)00165-4

Cited by 11 publications

(19 citation statements)

References 16 publications

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“…Seismic and geodetic measurements over the last decade have revealed that plate boundary strain can be accommodated by a spectrum of fault slip behavior (e.g., Miller et al, ; Peng & Gomberg, ; Wech et al, ). While earthquakes are the most dramatic end member of that spectrum, it has become increasingly clear that aseismic slip over a variety of timescales contributes significantly to total fault displacement in some tectonic settings (e.g., Bird et al, ; Dragert et al, ; Frohlich & Wetzel, ; Schwartz & Rokosky, ; Sobolev & Rundquist, ; Vidale & Houston, ). Understanding the partitioning of seismic versus aseismic displacement on faults is important from a hazards perspective, as unquantified aseismic slip adds uncertainty to risk assessments for faults with the potential to generate large earthquakes (e.g., Dixon et al, ; Linde et al, ; Linde & Silver, ).…”

Section: Introductionmentioning

confidence: 99%

Controls on Mid‐ocean Ridge Normal Fault Seismicity Across Spreading Rates From Rate‐and‐State Friction Models

et al. 2018

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Recent seismic and geodetic observations have led to a growing realization that a significant amount of fault slip at plate boundaries occurs aseismically and that the amount of aseismic slip varies across tectonic settings. Seismic moment release rates measured along the fast‐spreading East Pacific Rise suggest that the majority of fault slip occurs aseismically. By contrast, at the slow‐spreading Mid‐Atlantic Ridge seismic slip may represent up to 60% of total fault displacement. In this study, we use rate‐and‐state friction models to quantify the seismic coupling coefficient, defined as the fraction of total fault slip that occurs seismically, on mid‐ocean ridge normal faults and investigate controls on fault behavior that might produce variations in coupling observed at oceanic spreading centers. We find that the seismic coupling coefficient scales with the ratio of the downdip width of the seismogenic area (W) to the critical earthquake nucleation size (h*). At mid‐ocean ridges, W is expected to increase with decreasing spreading rate. Thus, the relationship between seismic coupling and W/h* predicted from our models explains the first‐order variations in seismic coupling coefficient as a function of spreading rate.

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Section: Introductionmentioning

confidence: 99%

Controls on Mid‐ocean Ridge Normal Fault Seismicity Across Spreading Rates From Rate‐and‐State Friction Models

et al. 2018

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“…Cowie et al [1993] later argued that seismic slip had to represent an insignificant fraction (<1%) of the time-averaged fault slip rate at the fast-spreading East Pacific Rise. Subsequent studies documented an exponential decrease in seismic moment release rates, and thus seismically accommodated strain, between slow and fast spreading centers [Sobolev and Rundquist, 1999;Rundquist and Sobolev, 2002;Bird et al, 2002;Frohlich and Wetzel, 2007]. This article is protected by copyright.…”

Section: Introductionmentioning

confidence: 99%

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

Olive

Escartı́n

2016

Geochem Geophys Geosyst

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Key points• Greater seismic moment release rates at detachment-bearing sections of the Mid-Atlantic Ridge compared to abyssal hill-bearing sections.• Coupled seismic thickness likely greatest (~2 km) at individual detachment faults of finite along-axis extent, and averages ~500 m elsewhere.• Rate and state friction theory attributes differences in seismic coupling to the thermomechanical state and lithology of oceanic normal faults. AbstractWhile normal faults are essential in shaping the seafloor formed at slow-spreading mid-ocean ridges, information on their behavior on short (seismic cycle) time scales is limited. Here we combine catalogs of hydro-acoustically and teleseismically recorded earthquakes to characterize the state of seismic coupling along the Northern Mid-Atlantic Ridge (MAR) between 12 and 35ºN. Along this portion of the MAR axis, tectonic extension is either taken up by steep conjugate faults that outline well-defined ridgeparallel abyssal hills, or dominantly by a large-offset detachment fault on one side of the axis.We investigate variations in seismicity and seismic moment release rates across thirty ridge sections that can be clearly characterized either as abyssal hill or detachment bearing. We find that detachment-bearing sections are associated with significantly greater seismicity and moment release rates than abyssal hill bearing sections, but show variability that may reflect the along-axis extent of individual detachment faults. Overall, the measured seismic moment release rates fail to account for the long-term fault slip rates. This apparent seismic deficit could indicate a mixed-mode of fault slip where earthquakes only account for ~10-30% of offset build-up at abyssal hill faults, while the rest is accommodated by some form of transient aseismic creep. We find this seismic coupling fraction to be significantly greater (~40-60%) at individual detachment systems, which is somewhat at odds with the common inference that detachment faults can sustain long-lived localized strain because they are weak. We therefore propose alternative interpretations for seismic coupling based on dynamic friction theory.

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“…On average, OTF seismic coupling varies between 10% and 30%; however, coupling may vary significantly along strike [ Boettcher and Jordan , ]. Earlier studies noted a decrease in coupling with spreading rate [e.g., Kawaski et al ., ; Sobolev and Rundquist , ; Bird et al ., ; Rundquist and Sobolev , ]. Using estimated fault length and slip rate values, the observed rupture area of the largest OTF earthquakes is less than the total area above the inferred 600°C isotherm.…”

Section: Introductionmentioning

confidence: 99%

Precise relative locations for earthquakes in the northeast Pacific region

2015

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Double‐difference methods applied to cross‐correlation measured Rayleigh wave time shifts are an effective tool to improve epicentroid locations and relative origin time shifts in remote regions. We apply these methods to seismicity offshore of southwestern Canada and the U.S. Pacific Northwest, occurring along the boundaries of the Pacific and Juan de Fuca (including the Explorer Plate and Gorda Block) Plates. The Blanco, Mendocino, Revere‐Dellwood, Nootka, and Sovanco fracture zones host the majority of this seismicity, largely consisting of strike‐slip earthquakes. The Explorer, Juan de Fuca, and Gorda spreading ridges join these fracture zones and host normal faulting earthquakes. Our results show that at least the moderate‐magnitude activity clusters along fault strike, supporting suggestions of large variations in seismic coupling along oceanic transform faults. Our improved relative locations corroborate earlier interpretations of the internal deformation in the Explorer and Gorda Plates. North of the Explorer Plate, improved locations support models that propose northern extension of the Revere‐Dellwood fault. Relocations also support interpretations that favor multiple parallel active faults along the Blanco Transform Fault Zone. Seismicity of the western half of the Blanco appears more scattered and less collinear than the eastern half, possibly related to fault maturity. We use azimuthal variations in the Rayleigh wave cross‐correlation amplitude to detect and model rupture directivity for a moderate size earthquake along the eastern Blanco Fault. The observations constrain the seismogenic zone geometry and suggest a relatively narrow seismogenic zone width of 2 to 4 km.

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Seismicity of oceanic and continental rifts—a geodynamic approach

Cited by 11 publications

References 16 publications

Controls on Mid‐ocean Ridge Normal Fault Seismicity Across Spreading Rates From Rate‐and‐State Friction Models

Controls on Mid‐ocean Ridge Normal Fault Seismicity Across Spreading Rates From Rate‐and‐State Friction Models

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

Precise relative locations for earthquakes in the northeast Pacific region

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