Contribution to crustal strain accumulation of minor faults: a case study across the Niigata–Kobe Tectonic Zone, Japan

Abstract

Recent global navigation satellite system (GNSS) data for the Japanese Islands have revealed a high-strain-rate region suggesting the existence of a region of broad-scale crustal deformation. The Niigata-Kobe Tectonic Zone (NKTZ), which is the high-strain-rate zone in central Japan, shows a short-term dextral strain rate of ~ 12 mm/year. The total slip rate of the Quaternary fault zones in the NKTZ has been estimated as ~ 6.7 mm/year, accounting for just over half the short-term strain rate of the zone. However, this slip rate underestimates the total slip rate on faults within the NKTZ owing to possible distributed deformation on minor faults. This study quantifies the slip rate attributable to these other faults in the southeastern-central NKTZ and reveals the unique deformation structure across the highstrain-rate zone, which comprises a Quaternary fault core, a Quaternary fault damage zone, an incipient brittle shear zone (active background), and an inactive background. The spatial characteristics of the incipient brittle shear zone can be explained in terms of fault density, which increases toward the central NKTZ. Minor faults located > 500 m from major Quaternary faults but within the NKTZ have sense of shear consistent with that of the major faults. In contrast, minor faults outside of the NKTZ show sense of shear that differ from the dextral displacement of the high-strain-rate zone and do not contribute to the slip rate of the zone. The total slip rate of minor faults in the southeastern-central NKTZ is estimated to be 0.46-2.88 mm/year (roughly equal to a major Quaternary fault in the zone), which implies 4-24% of crustal strain is stored in the active background.

The Entire Crust can be Seismogenic: Evidence from Southern Malawi

“…The processes by which tectonic strain is accumulated vary with depth in the crust, and this depth variation is controlled by a combination of factors including crustal composition, geothermal gradient and tectonic strain rate (e.g., Burov, 2011;Tamura et al, 2020;Zielke et al, 2020). In some countries, such as the USA, dense networks of broadband seismometers accurately record the location of decades worth of microseismic data which can be used to refine the geometry of models of active faulting, and can help to infer the depth extent of velocity-weakening behavior which can lead to large and damaging earthquakes (e.g., Ross et al, 2020;Smith-Konter et al, 2011).…”

Analysis of the Stress Field Around Concealed Active Fault From Minor Faults‐Slip Data Collected by Geological Survey: An Example in the 1984 Western Nagano Earthquake Region

“…However, the multiple inverse method results for recently active minor faults are consistent with the current stresses in the area (Niwa et al, 2024;Tamura et al, 2020). Tamura et al (2020) used this method to show that the activity of geological faults distributed within the Niigata-Kobe Tectonic Zone (NKTZ) is consistent with the current stresses. Niwa…”

“…This method has been used primarily to recover stresses during fault activity, such as on geological faults that are thought to have been active in older times (Abe & Sato, 2021;Haji & Yamaji, 2021;Otsubo et al, 2009;Yamaji, 2000b). However, the multiple inverse method results for recently active minor faults are consistent with the current stresses in the area (Niwa et al, 2024;Tamura et al, 2020). Tamura et al (2020) used this method to show that the activity of geological faults distributed within the Niigata-Kobe Tectonic Zone (NKTZ) is consistent with the current stresses.…”

High-Resolution Three-dimensional Azimuthal Velocity Anisotropy of S-waves in southwest Japan, based on Ambient Noise Tomography

“…The NKTZ, just like the Kinki Triangle (Fig. 1c), hosts NE-SW-striking Quaternary fault zones which are oriented in the same direction as the NKTZ (Tamura et al 2020) and many destructive earthquakes have occurred in this zone.…”