New Empirical Earthquake Source‐Scaling Laws

Abstract

We develop new empirical scaling laws for rupture width W, rupture length L, rupture area A, and average slip D, based on a large database of rupture models. The database incorporates recent earthquake source models in a wide magnitude range (M w 5.4-9.2) and events of various faulting styles. We apply general orthogonal regression, instead of ordinary least-squares regression, to account for measurement errors of all variables and to obtain mutually self-consistent relationships. We observe that L grows more rapidly with M w compared to W. The fault-aspect ratio (L=W) tends to increase with fault dip, which generally increases from reversefaulting, to normal-faulting, to strike-slip events. At the same time, subduction-interface earthquakes have significantly higher W (hence a larger rupture area A) compared to other faulting regimes. For strike-slip events, the growth of W with M w is strongly inhibited, whereas the scaling of L agrees with the L-model behavior (D correlated with L). However, at a regional scale for which seismogenic depth is essentially fixed, the scaling behavior corresponds to the W model (D not correlated with L). Selfsimilar scaling behavior with M w − log 10 A is observed to be consistent for all the cases, except for normal-faulting events. Interestingly, the ratio D=W (a proxy for average stress drop) tends to increase with M w , except for shallow crustal reversefaulting events, suggesting the possibility of scale-dependent stress drop. The observed variations in source-scaling properties for different faulting regimes can be interpreted in terms of geological and seismological factors. We find substantial differences between our new scaling relationships and those of previous studies. Therefore, our study provides critical updates on source-scaling relations needed in seismic-tsunami-hazard analysis and engineering applications. Electronic Supplement: Figures depicting regression analysis, normality probability plots, and comparisons between different source-scaling relationships; and tables listing rupture models and different earthquake source-scaling relationships.

Coseismic Slip Vectors of 24 August and 30 October 2016 Earthquakes in Central Italy: Oblique Slip and Regional Kinematic Implications

“…The Mw 6.5 30 October event fits well with the predicted L according to both surface ruptures extend (~25‐km‐long distance; Figure a; Civico et al ; Villani et al , ) and rupture models inverted from strong‐motion and geodetic data (20‐ to 27‐km fault plane length; Cheloni et al, ; Chiaraluce et al, ; Pizzi et al, ). Thingbaijam et al () predict a rupture length L ~15 km for a Mw 6.0 earthquake. Rupture models for Mw 6.0 24 August event involve 20–25 km of fault plane length (Cheloni et al, ; Chiaraluce et al, ), suggesting a larger‐than‐average length/Mw ratio for this earthquake.…”

“…Concerning surface rupture length and recent empirical earthquake source‐scaling relationships based on a large database of rupture models (including 29 rupture models for normal faulting events), Thingbaijam et al () suggest that a Mw 6.5 earthquake would produce a rupture length L ~27 km. The Mw 6.5 30 October event fits well with the predicted L according to both surface ruptures extend (~25‐km‐long distance; Figure a; Civico et al ; Villani et al , ) and rupture models inverted from strong‐motion and geodetic data (20‐ to 27‐km fault plane length; Cheloni et al, ; Chiaraluce et al, ; Pizzi et al, ).…”

Spatiotemporal Seismic Hazard and Risk Assessment of Aftershocks ofM 9 Megathrust Earthquakes

“…For example, according to Ogata and Zhuang (2006), the performances of the isotropic and anisotropic spatial distributions are similar for the offshore Tohoku region from 1926 to 1995 with a maximum Mj = 7.9 in the historical catalog. In addition, recent empirical scaling laws by Thingbaijam et al (2017) indicate that differences between fault width and fault length of subduction-interface events are indistinguishable when M < 7.5. When the magnitude exceeds M8, however, the fault length is generally greater than the fault width.…”

“…(3) The dip and strike angles are sampled from uniform distributions between 10º-13º and 195º-203º, respectively, selected from available rupture models of the Tohoku earthquake (Koketsu et al, 2011;Shao et al, 2011;Suzuki et al, 2011;Yagi and Fukahata, 2011). 4The rupture lengths and widths are sampled from the empirical scaling laws of Thingbaijam et al (2017) with a covariance between rupture length and width from Goda et al (2016). By having the sampled epicenter, and strike and slip angles, the location of the rupture area is calculated assuming a bilateral rupture.…”

“…In the simulation framework, x0 and y0 are assumed to equal the mainshock epicenter of a bilateral rupture area. The sampled rupture length and width from the empirical scaling law (Thingbaijam et al, 2017) can be applied to the 2D Gaussian distribution by scaling the standard deviations.…”