Supplemental Material: How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?

Text S1: Bayesian (OxCal) models for northern Lost River fault zone trench sites. Text S2: Bulk sediment analysis and charcoal identification; Text S3: Luminescence geochronology. Table S1: Description of stratigraphic units at the Sheep Creek trench. Table S2: Description of stratigraphic units at the Arentson Gulch trench. Figure S1: Photomosaics and large-format trench logs for the Sheep Creek trench. Figure S2: Photomosaics and large-format trench logs for the Arentson Gulch trench. Figure S3: Sheep Creek and Arentson Gulch vertical displacement measurements. Figure S4: Fault bend angles along the northern Lost River fault zone. Figure S5: Photographs of the Sheep Creek and Arentson Gulch trench sites. Figure S6: Probability density functions for Lost River fault zone ruptures.

Supplemental Material: How similar was the 1983 Mw 6.9 Borah Peak earthquake rupture to its surface-faulting predecessors along the northern Lost River fault zone (Idaho, USA)?

Text S1: Bayesian (OxCal) models for northern Lost River fault zone trench sites. Text S2: Bulk sediment analysis and charcoal identification; Text S3: Luminescence geochronology. Table S1: Description of stratigraphic units at the Sheep Creek trench. Table S2: Description of stratigraphic units at the Arentson Gulch trench. Figure S1: Photomosaics and large-format trench logs for the Sheep Creek trench. Figure S2: Photomosaics and large-format trench logs for the Arentson Gulch trench. Figure S3: Sheep Creek and Arentson Gulch vertical displacement measurements. Figure S4: Fault bend angles along the northern Lost River fault zone. Figure S5: Photographs of the Sheep Creek and Arentson Gulch trench sites. Figure S6: Probability density functions for Lost River fault zone ruptures.

Investigation of the Cape Fear arch and East Coast fault system in the Coastal Plain of North Carolina and northeastern South Carolina, USA, using LiDAR data

LiDAR data collected in the Coastal Plain of the Carolinas revealed numerous, mostly NW-SE-oriented lineaments that cross the Cape Fear arch, the longest of which are the 50- to 115-km-long, NW-SE-oriented Faison, Jarmantown, Livingston Creek, and White Marsh lineaments and the ~50-km-long, ENE-WSW-oriented Tomahawk lineament in southeastern North Carolina. Their interpretation is based mainly on locally incised channels, abrupt stream bends, topographic scarps, and linear areas of uplifted Coastal Plain sediments. The Precambrian to Paleozoic Graingers basin or synform in the pre-Cretaceous basement terminates to the southwest along the ~28-km-long, 3- to 7-km-wide Jarmantown high. The ~115-km-long Jarmantown lineament may be the surface expression of the previously reported Neuse fault, the location of which has been controversial. The Jarmantown and other lineaments crossing the Cape Fear arch suggest that the arch is structurally complex. Further investigation of the East Coast fault system (ECFS) along the west side of the Cape Fear arch in North Carolina revealed that it is located farther to the northwest than previously reported, thereby making it continuous with the ECFS in northeastern South Carolina where it forms a ~15° restraining bend. We postulate that the interpreted faults crossing the Cape Fear arch in southeastern North Carolina formed to compensate for the increased compression and change in volume from dextral motion along the fault bend. Holocene paleoliquefaction deposits near the coast, a vertically offset Pleistocene(?) beach ridge along the interpreted Faison fault, and Tertiary surface faults along the ECFS northeast of Smithfield, North Carolina, suggest that large Quaternary earthquakes may have occurred along the ECFS, the Faison and Neuse faults, and other interpreted faults that cross the Cape Fear arch.

The Role of Frontal Thrusts in Tsunami Earthquake Generation

ABSTRACT The frontal sections of subduction zones are the source of a poorly understood hazard: “tsunami earthquakes,” which generate larger-than-expected tsunamis given their seismic shaking. Slip on frontal thrusts is considered to be the cause of increased wave heights in these earthquakes, but the impact of this mechanism has thus far not been quantified. Here, we explore how frontal thrust slip can contribute to tsunami wave generation by modeling the resulting seafloor deformation using fault-bend folding theory. We then quantify wave heights in 2D and expected tsunami energies in 3D for both thrust splays (using fault-bend folding) and down-dip décollement ruptures (modeled as elastic). We present an analytical solution for the damping effect of the water column and show that, because the narrow band of seafloor uplift produced by frontal thrust slip is damped, initial tsunami heights and resulting energies are relatively low. Although the geometry of the thrust can modify seafloor deformation, water damping reduces these differences; tsunami energy is generally insensitive to thrust ramp parameters, such as fault dip, geological evolution, sedimentation, and erosion. Tsunami energy depends primarily on three features: décollement depth below the seafloor, water depth, and coseismic slip. Because frontal ruptures of subduction zones include slip on both the frontal thrust and the down-dip décollement, we compare their tsunami energies. We find that thrust ramps generate significantly lower energies than the paired slip on the décollement. Using a case study of the 25 October 2010 Mw 7.8 Mentawai tsunami earthquake, we show that although slip on the décollement and frontal thrust together can generate the required tsunami energy, <10% was contributed by the frontal thrust. Overall, our results demonstrate that the wider, lower amplitude uplift produced by décollement slip must play a dominant role in the tsunami generation process for tsunami earthquakes.

INTERPRETAÇÃO SÍSMICA E MODELAGEM 3D ESTRUTURAL NA BACIA DE BARREIRINHAS (MARANHÃO, BRASIL)

Discoveries of hydrocarbons in the basins of the African Equatorial Margin and Guinea Gulf stimulated the exploratory interest in the basins of the Brazilian Equatorial Margin, for being together before the Continental Drift. This interest emerges because both African and South American equatorial margin are considered analogous. The Barreirinhas Basin is a member of the Brazilian equatorial margin. The objective of this work is to present the results obtained through the seismic interpretation and structural 3D modeling, in the context of gravitational tectonics, in an area covered by 3D seismic data, in the Barreirinhas Basin. The compressional domain of an extensive-compressive system was mapped. In this study, were identified reverse faults, thrust faults and fault-related folding like fault-bend and fault-propagation fold that can be accompanied by backthrust features in deep to ultra-deep waters. The 3D structural model allowed the representation of the geometric variations present in the study area. The new information will be important for the identification and evaluation of structures with greater potential for hydrocarbon accumulations and can help in future studies to characterize the reservoir, contributing to the evolution of knowledge of the equatorial margin, especially in the Barreirinhas Basin.

Pure Void Space and Fracture Pore Space in Fault-Fractured Zones

Fault-fractured pore space is complex and difficult to predict and evaluate. For a single independent ramp-flat fault-bend fold structure, the pure void space between two fault walls equals the integrated fracture pore spaces within the fault damage zone if it were concentrated on the fault plane. Using an area balancing technique and geometrical relationship, we have developed a two-dimensional (2D) model to calculate the pore space of fractures associated with fault development. The development and distribution of fault detachment voids or fault fracture pore space are controlled by the physical properties of the deforming medium, mechanics of deformation, and geometry of a fault-ramp structure. We demonstrate how concordant or discordant folding of the fault wall rock affects the nature of fault-fracture pore space. The pure void space and fracture pores in the fault zone can be quantitatively described by the following parameters: initial ramp angle and height, overlap ramp length, throw and slipping displacement, stack thickness, curvature and derivation of the angle between bed and fault plane (Rθ), and dip isogons. Rθ reflects the conformity of two opposite fault sections and the folding accordance of two walls, and it is a key element for the development and distribution of fracture pore space in a fault zone. Furthermore, we observed natural outcrops supporting and validating our model assumptions in the foreland fault system, Central China.

Incremental shortening calculation of the mixed-shear fault-bend folds

<p>Shear fault-bend folds are characterized by a long back-limb that dips more gently than the fault ramp [1]. During the folding growth, the back limb rotates and widens progressively through a combination of limb rotation and kink-band migration. Two end-member models of shear fault-bend folding theories, including simple-shear fault-bend folding (C=0.5) and pure-shear fault-bend folding (C=1), have been developed and widely applied. Mixtures of pure and simple shear (0.5<C<1) are possible and have been found in the natural. Few quantitative methods to limit the shear-index (C) of the shear fault-bend folds so far. The incremental shortening can be calculated based on a simplified equation that assumes the linear relationship between the shortening and the limb rotation angle of the back limb [2]. However, the relationship of these two parameters is nonlinear according to the shear fault-bend folding theory [1]. Calculation results of the linear model have large uncertainty.</p><p>Here, we develop a method to calculate the shear-index (C), providing an idea to improve the mixed-shear fault-bend fold models, and establishing a formula to calculate the incremental shortening based on the nonlinear relationship between the back-limb dip angle and the shortening. It is a more general method to calculate the incremental shortening of the shear fault-bend folds.</p><p>This model has been applied to the Tugulu anticline in the northern foreland of Chinese Tian Shan, which is a mixed-shear fault-bend fold based on previous studies [3]. Through an analysis of deformed fluvial terraces and growth strata, we develop the shortening history of the Tugulu anticline along the Hutubi River using our developed nonlinear model. Our results show that the Tugulu anticline has a shear-index of ~0.91 and a steady shortening rate of ~1.5mm/yr over the last 500ka.</p><p>References:</p><ul><li>[1] Suppe et al. (2004) AAPG Memoir 82: 303-323.</li> <li>[2] Yue et al. ( 2011) AAPG Memoir 94: 153–186.</li> <li>[3] Qiu et al. ( 2019) Tectonophysics 772:228209.</li> </ul>

Lower Portion Rupture of a Thrust Fault during the 2017 Mw 6.3 Jinghe Earthquake: Implications to Seismic Hazards in the Tian Shan Region

The 2017 Mw 6.3 Jinghe earthquake represents one of the few large earthquakes that are well recorded by seismic instruments and Interferometric Synthetic Aperture Radar (InSAR) observations in the seismically active Tian Shan region. In this study, we use the rupture fault solution (dip, dip direction, and slip sense) from seismologic and InSAR results, along with analysis of our collected surface mapping data, to determine the subsurface fault-plane geometry of the seismogenic Jinghenan fault. This geometric model, integrated with the coseismic slip distribution from seismologic and InSAR data, reveals that: (1) the Jinghenan fault extends downward from the land surface at a dip of ∼46° S (upper ramp), then bends to ∼42° S (lower ramp) at the depth of 9–13 km; (2) the coseismic rupture is confined within the Jinghenan lower ramp, and its upper limitation is approximately coincident with the fault-bend location. This coseismic rupture pattern and seismic behavior can be broadened to other active thrust faults within the Tian Shan, suggesting that, during moderate-strong earthquakes, such faults may only rupture partially in the down-dip extension, and the unruptured fault portion remains to pose high-seismic risk in the future.