Estimated likelihood of observing a large earthquake on a continental low-angle normal fault and implications for low-angle normal fault activity

Abstract

The lack of observed continental earthquakes that clearly occurred on low‐angle normal faults (LANFs) may indicate that these structures are not seismically active or that these earthquakes are simply rare events. To address this, we compile all potentially active continental LANFs (24 in total) and calculate the likelihood of observing a significant earthquake on them over periods of 1–100 years. This probability depends on several factors including the frequency‐magnitude distribution. For either a characteristic or Gutenberg‐Richter distribution, we calculate a probability of about 0.5 that an earthquake greater than M6.5 (large enough to avoid ambiguity in dip angle) will be observed on any LANF in a period of 35 years, which is the current length of the global centroid moment tensor catalog. We then use Bayes' Theorem to illustrate how the absence of observed significant LANF seismicity over the catalog period moderately decreases the likelihood that the structures generate large earthquakes.

Regional‐Scale Low‐Angle Normal Fault Friction and Cohesion Constrained From Mohr‐Coulomb Models of Active and Abandoned Range‐Front Faults in Papua New Guinea

“…Low‐angle normal faults (LANFs) are normal faults that slip at dip angles of <30°. Active examples are globally uncommon (e.g., Collettini, 2011; Hayman et al., 2003; Styron & Hetland, 2014; Webber et al., 2018), as are earthquakes demonstrably sourced on such structures (e.g., Abers, 1991; Axen, 2004; Collettini & Sibson, 2001; Wernicke, 1995). Low‐angle normal faults typically accrue large finite offsets (10s of km) and juxtapose rocks formed at contrasting structural depths to form metamorphic core complexes (MCCs; e.g., Lister & Davis, 1989; Whitney et al., 2013).…”

Extent of Low‐Angle Normal Slip in the 2010 El Mayor‐Cucapah (Mexico) Earthquake From Differential Lidar

“…This is an important issue for a variety of reasons. First, normal slip along gently dipping fault planes is mechanically unfavorable (e.g., Anderson, , ) and resolving the extent of it in the El Mayor‐Cucapah earthquake is thus important for the long‐standing debate over whether low‐angle normal faults host large earthquakes (e.g., Abers, ; Axen, ; Jackson & White, ; Proffett, ; Styron & Hetland, ; Wernicke, ) and whether multifault ruptures provide a mechanism by which they can do so (Fletcher et al, ). Second, there are regional implications for how oblique extension is accommodated along this section of the Pacific‐North America plate boundary (Axen et al, ; Fletcher & Spelz, ; Mueller et al, ; Nagy et al, ).…”

Geologic map of the east-central Meadow Valley Mountains, and implications for reconstruction of the Mormon Peak detachment, Nevada

“…Extensional detachments (nominally, low-angle normal faults with displacements of kilometers to tens of kilometers) are widely described in the literature and currently accepted by most earth scientists as fundamental tectonic elements (e.g., Lister and Davis, 1989;Abers, 1991;Rigo et al, 1996;Chiaraluce et al, 2007;Bidgoli et al, 2015). However, they are problematic, not only from a mechanical point of view, but also from the point of view of historical seismicity, which is dominated by slip on planes steeper than 30° (e.g., Jackson and White, 1989;Wernicke, 1995;Elliott et al, 2010;Styron and Hetland, 2014). Thus, despite general acceptance, the very existence of lowangle normal faults continues to be challenged, in some cases even on geo logical grounds (e.g., Miller et al, 1999;Anders et al, 2006;Wong and Gans, 2008).…”