Systematic survey of high‐resolutionbvalue imaging along Californian faults: Inference on asperities

Abstract

Understanding and forecasting earthquake occurrences is presumably linked to understanding the stress distribution in the Earth's crust. This cannot be measured instrumentally with useful coverage. However, the size distribution of earthquakes, quantified by the Gutenberg‐Richter b value, is possibly a proxy to differential stress conditions and could therewith act as a crude stress‐meter wherever seismicity is observed. In this study, we improve the methodology of b value imaging for application to a high‐resolution 3‐D analysis of a complex fault network. In particular, we develop a distance‐dependent sampling algorithm and introduce a linearity measure to restrict our output to those regions where the magnitude distribution strictly follows a power law. We assess the catalog completeness along the fault traces using the Bayesian Magnitude of Completeness method and systematically image b values for 243 major fault segments in California. We identify and report b value structures, revisiting previously published features, e.g., the Parkfield asperity, and documenting additional anomalies, e.g., along the San Andreas and Northridge faults. Combining local b values with local earthquake productivity rates, we derive probability maps for the annual potential of one or more M6 events as indicated by the microseismicity of the last three decades. We present a physical concept of how different stressing conditions along a fault surface may lead to b value variation and explain nonlinear frequency‐magnitude distributions. Detailed spatial b value information and its physical interpretation can advance our understanding of earthquake occurrence and ideally lead to improved forecasting ability.

The seismo-hydromechanical behavior during deep geothermal reservoir stimulations: open questions tackled in a decameter-scale in situ stimulation experiment

“…Schorlemmer et al (2005) examined the b values of earthquakes in different stress regimes and found that lower values correlated with areas of higher differential stress. Similar trends have been reported for induced seismicity (Bachmann et al, 2012) but also in tectonic earthquakes (Tormann et al, 2014(Tormann et al, , 2015Spada et al, 2013) and laboratory experiments (Amitrano, 2012;Goebel et al, 2012). Thus, it was hypothesized that b values are related to local stress conditions (Scholz, 2015), or -in the context of induced earthquakes -to a combination of pressure and stress conditions.…”

Randomness of megathrust earthquakes implied by rapid stress recovery after the Japan earthquake

“…Indeed, the correlation between b-value and stress as observed in laboratory experiments 3,4 , and indicated by this and previous seismicity studies 6-8 , is not unique: what drives the increase of the relative frequency of large events in a particular area-that is, the likelihood that small asperities preferably break together, rather than one by one 7,15 ? Whereas the stress level is an intuitive key parameter, other different factors have been suggested to play a role, such as the degree of material heterogeneity 31 , or the degree of stress concentration (proportional to the product of stress and the square root of the length of the nucleating fracture) 32 .…”

Influences on the location of repeating earthquakes determined from a and b value imaging

“…Such high rates of microseismicity are commonly observed in creeping faults [Scholz, 1990;Malservisi et al, 2005], where strain is accumulated in the transition zone from locked to creeping patches [Vidale et al, 1994;Nadeau et al, 1995;Sammis and Rice, 2001;Waldhauser and Ellsworth, 2002]. However, these statistical relationships vary by style of faulting, tectonic loading rate, and aseismic slip behavior [Amelung and King, 1997;Wyss et al, 2004;Schorlemmer et al, 2005;Tormann et al, 2014]. The predominantly high b value (>1.2) and D~2b have been proposed as more suitable descriptors of the creeping portion of the fault [Wyss et al, 2004].…”