Hypocenter Locations in Finite-Source Rupture Models

Abstract

We use a database of more than 80 finite-source rupture models for more than 50 earthquakes (M w 4.1-8.1) with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip. Rupture in strike-slip and crustal dip-slip earthquakes tends to nucleate in the deeper sections of the fault; subduction earthquakes do not show this tendency. Ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement. Rupture nucleates in regions of very large slip (D Ն 2/3 D max ) in only 16% of the events, in regions of large slip (1/3 D max Ͻ D Ͻ 2/3 D max ) in 35% of the events, and in regions of low slip (D Յ 1/3 D max ) in 48% of the events. These percentages significantly exceed the percentages of fault area with very large (ϳ7%) and large (ϳ28%) slip. Ruptures that nucleate in regions of low slip, however, tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length. Applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip.

Testing stress shadowing effects at the South American subduction zone

“…For all other cases (historical records), the catalogue location defines the centroid location of the damages and thus the centre of the rupture. The true epicentre (nucleation point) of the earthquake is then assumed to be randomly located within the two rupture ends according to a normal distribution which is adapted to the empirically observed distribution of the relative position of the epicentres within ruptures (Mai et al 2005). The adapted distribution is illustrated in the inset of Fig.…”

“…If only the epicentre or centroid location is recorded in the catalogue, the rupture ends are estimated in two steps: (i) The length of the ruptures are selected according to the empirical distribution of Blaser et al (2010) for subduction events, which includes the spread of the empirical data for a given earthquake magnitude. (ii) The relative position of the epicentre within the rupture is randomly chosen from the normal distribution adapted to the empirical data (Mai et al 2005, inset of Fig. 3).…”

“…The rupture can be unilateral or bilateral. This is decided by taking the position of the epicentre randomly from a normal distribution which is adapted to the empirically observed distribution of the relative epicentre position within ruptures (Mai et al 2005, see inset of Fig. 3).…”

Quantifying variability in earthquake rupture models using multidimensional scaling: application to the 2011 Tohoku earthquake

“…In this study, we choose the intensity levels following Mai et al (2005) who defined the slip heterogeneity based on a large set of finite-fault rupture models. They found that earthquake rupture tends to start close to a region they defined as a large-slip area ( 1 3 U max < U < 2 3 U max , where U is the slip value and U max is the maximum slip).…”

Estimation of ground motion during the 18th September 2011 Sikkim Earthquake

“…From the derived correlation lengths, slip is simulated as a random field by the spectral representation method of Shinozuka and Deodatis (1996). The hypocentre in each case is taken nearer to the regions of maximum slip release (Mai et al 2005). This sample slip field on the fault plane is discretized into subfaults of size 1 km 6 1 km and seismic moment of each point source is computed using Equation 8.…”