Synthesis of Recent Paleoseismic Research on Quaternary Faulting in the Eastern Tennessee Seismic Zone, Eastern North America: Implications for Seismic Hazard and Intraplate Seismicity

ABSTRACT Causes of intraplate seismicity remain a great unsolved problem, in contrast with plate-boundary seismicity. Modern seismicity records frequent seismic activity in plate-boundary seismic zones, but in fault zones where seismic activity is not frequent, plate boundary or intraplate, resolution of prehistoric earthquake activity is critical for estimating earthquake recurrence interval and maximum expected magnitude. Thus, documenting prehistoric earthquakes is crucial for assessing earthquake hazard posed to infrastructure, including nuclear reactors and large dams. The ∼400 km long eastern Tennessee seismic zone (ETSZ), United States, is the third most active seismic zone east of the Rocky Mountains in North America, although the largest recorded ETSZ earthquake is only Mw 4.8. Ironically, it is the least studied major eastern U.S. seismic zone. Recent ETSZ field surveys revealed an 80 km long, 060°-trending corridor containing northeast-striking Quaternary thrust, strike slip, and normal faults with displacements ≥1 m. It partially overlaps a parallel trend of seismicity that extends 30 km farther southwest, suggesting this active faulting zone may extend ∼110 km within part of the ETSZ. Near Dandridge, Tennessee, a thrust fault in French Broad River alluvium records two earthquakes in the last 40,000 yr. About 50 km southwest near Alcoa, Tennessee, a thrust fault cuts Little River alluvium and records two earthquakes between 15,000 and 10,000 yr ago. About 30 km farther southwest at Vonore, Tennessee, a thrust fault displaces bedrock ≥2 m over colluvium, and alluvium is normal faulted >2 m. This corridor, just west of the Blue Ridge escarpment, overlies a steep gradient in midcrustal S-wave velocities, consistent with a basement fault at hypocentral depths. The corridor faults may be connected to a basement fault or localized coseismic faults above a blind basement fault. Our current data suggest at least two Mw≥6.5 surface rupturing events in the last 40,000 yr.

Supplemental Material: Late Quaternary active faulting on the inherited Baoertu basement fault within the eastern Tian Shan orogenic belt: Implications for regional tectonic deformation and slip partitioning, NW China

Figure S1: Profile of velocity components normal to structure striking (E-W components) across the eastern Tian Shan (profile from (85.3°, 41.0°) to (85.3°, 45.0°) with a width of 240 km.

Supplemental Material: Late Quaternary active faulting on the inherited Baoertu basement fault within the eastern Tian Shan orogenic belt: Implications for regional tectonic deformation and slip partitioning, NW China

Figure S1: Profile of velocity components normal to structure striking (E-W components) across the eastern Tian Shan (profile from (85.3°, 41.0°) to (85.3°, 45.0°) with a width of 240 km.

Cadomian orogenic collapse in the Ibor and Alcudia anticlines of the Central Iberian Zone, Spain

In the Central Iberian Zone, the Cadomian orogenic collapse is represented by chaotic megabreccias, olistostromes and mélange deposits reflecting a drastic change from slope-related deposits, fed by denudation of the Cadomian arc, to offshore-dominant settings episodically punctuated by phosphogenetic processes. In the Ibor and Alcudia anticlines, the pre-rift unconformity is marked by paraconformable to angular discordant contacts separating variable tilted strata of the Ediacaran Lower Alcudian – Domo Extremeño Supergroup and the upper Ediacaran – lower Terreneuvian Ibor Group from the overlying Terreneuvian San Lorenzo and Fuentepizarra formations. The sedimentation of the San Lorenzo Formation reflects two palaeogeographic scenarios: (i) a low-angle stable basement recording shoaling-upward siliciclastic cycles, and (ii) perturbations of basement fault scarps feeding slope-related conglomeratic channels, with NE-directed palaeocurrents, and sourced from topographic palaeohighs controlled by the movement along synsedimentary normal fault systems, such as the so-called El Guijo Fault. The intra-Fortunian age of the pre-rift unconformity is constrained by the ichno- and microfossil content of the succession, and is bracketed between the first occurrence of Treptichnus pedum in the Arrocampo Formation (Ibor Group) and of Anabarella plana in the Fuentepizarra Formation.

Diffraction imaging for basement fault-fracture prediction: Application to an oil field in Cuu Long basin

Improvement to the image of fractured granite basements is among the most sought-after goals for processing seismic data in Cuu Long basin, the most proliferous petroleum basin. Unlike a clear layering structure of the sediment, fuzzy images of the granite basement are often the source of confusion for interpreters to identify which structures are presented inside it. In such a low signal to noise ration (SNR) environment, extracting geological information such as fault systems and fracture becomes challenging. In this study, diffraction imaging is employed in an effort to identify and enhance the fault system inside the basement. The comparison of the study result with various standard post-stack attribute approaches shows the effectiveness of the diffraction imaging method.

Diffraction imaging for basement fault-fracture prediction: Application to an oil field in Cuu Long basin

Improvement to the image of fractured granite basements is among the most sought-after goals for processing seismic data in Cuu Long basin, the most proliferous petroleum basin. Unlike a clear layering structure of the sediment, fuzzy images of the granite basement are often the source of confusion for interpreters to identify which structures are presented inside it. In such a low signal-to-noise ratio (SNR) environment, extracting geological information such as fault systems and fracture becomes challenging. In this study, diffraction imaging is employed in an effort to identify and enhance the fault system inside the basement. The comparison of the study result with various standard post-stack attribute approaches shows the effectiveness of the diffraction imaging method.