Determination of the Youngest Active Domain in Major Fault Zones Using Medical X-ray Computed Tomography-derived Density Estimations

Abstract Determination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover are critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the youngest active domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples, and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone is approached, such that the region with the lowest CT number and rock/protolith density ratio defines the youngest active domain of a given fault zone.

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Quantitative determination of the lowest density domain in major fault zones via medical X-ray computed tomography

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00442-7 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Akiyuki Iwamori ◽

Hideo Takagi ◽

Nobutaka Asahi ◽

Tatsuji Sugimori ◽

Eiji Nakata ◽

...

Keyword(s):

Fault Zone ◽

Atomic Number ◽

Density Ratio ◽

Effective Atomic Number ◽

Fault Zones ◽

Ct Number ◽

Fault Rock ◽

Major Fault ◽

X Ray Computed

AbstractDetermination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover is critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here, we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the lowest density domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone, identified by outcrop observation, are approached, such that the region with the lowest CT number and rock/protolith density ratio defines the lowest density domain of a given fault zone. We also discuss the relationship between the lowest density domain and the youngest active domain in major fault zones and investigate the points to be considered when the youngest active domain is identified from the lowest density domain determined by the CT number.

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Carbonate clumped isotope thermometry of fault rocks and its possibilities: tectonic implications from calcites within Himalayan Frontal Fold-Thrust Belt

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00435-6 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Dyuti Prakash Sarkar ◽

Jun-ichi Ando ◽

Akihiro Kano ◽

Hirokazu Kato ◽

Gautam Ghosh ◽

...

Keyword(s):

Fault Zone ◽

Analytical Techniques ◽

Fault Zones ◽

Low Grade ◽

Fault Rock ◽

Fault Rocks ◽

Main Boundary Thrust ◽

Element Partitioning ◽

Clumped Isotope ◽

Northwest India

AbstractDisentangling the temperature and depth of formation of fault rocks is critical for understanding their rheology, exhumation, and the evolution of fault zones. Estimation of fault rock temperatures mostly relies on conventional geothermometers of metamorphic minerals and element partitioning analysis, which are largely inapplicable in shallow crustal fault rocks. Here, we demonstrate the applicability of the carbonate clumped isotope thermometer in low-grade carbonate-bearing fault rocks from the Himalayan frontal wedge (northwest India). Coalescing carbonate clumped isotope thermometry and calcite e-twin morphology allows us to constrain the temperature and depth of formation of the two main thrusts of the Himalayan frontal wedge, the Nahan thrust (170 ± 10 °C; 6–7 km depth), and the Main Boundary thrust (262 ± 30 °C; 10–11 km depth). The integration of the adopted analytical techniques can promote the application of calcite-based clumped isotope thermometry to the fault zone processes and refinement of shallow crustal fault zone models.

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Geomorphological reconnaissance of the Psathopyrgos and Rion-Patras Fault zones (Achaia, NW Peloponnesus).

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.17063 ◽

2007 ◽

Vol 40 (4) ◽

pp. 1586 ◽

Cited By ~ 5

Author(s):

N. Palyvos ◽

D. Pantosti ◽

L. Stamatopoulos ◽

P. M. De Martini

Keyword(s):

Fault Zone ◽

Fault Zones ◽

Fault Slip ◽

Geological Data ◽

Slip Rates ◽

The Holocene ◽

Fault Slip Rates ◽

Earthquake Ruptures ◽

Surficial Deposits

In this communication we discuss reconnaissance geomorphological observations along the active Psathopyrgos and Rion-Patras (NE part) fault zones. These fault zones correspond to more or less complex rangefronts, the geomorphic characteristics of which provide hints on the details of the fault zone geometries, adding to the existing geological data in the bibliography. Aiming at the identification of locations suitable or potentially suitable for geomorphological and geological studies for the determination of fault slip rates in the Holocene, we describe cases of faulted Holocene landforms and associated surficial deposits. We also discuss problems involved in finding locations suitable for geological (paleoseismological) studies for the determination of the timing of recent earthquake ruptures, problems due to both man-made and natural causes.

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