Comparison of seismic moment release rates along different types of plate boundaries

Abstract

S U M M A R YThis is a global survey of seismic moment release rates (scalar moment/length/time) along five categories of plate boundaries; for shallow earthquakes we evaluate divergent, transcurrent and convergent boundaries; for deep earthquakes we consider separately boundaries where the deepest seismicity is intermediate (<300 km) or deep-focus (500-600 km). The objective is to evaluate the typical range of rates observed and present the results in a form where it is straightforward to compare factors that affect rates in the different environments. For earthquakes occurring 1977-2005, the data are scalar moments from the global centroid moment tensor catalogue; for earthquakes 1900-1976, we use a standard formula to obtain moment from magnitudes in the Engdahl-Villaseñor Centennial catalogue. Moment release rates correlate with relative velocity between plates along divergent and transcurrent boundaries; focal depth influences moment release rates along intermediate and deep-focus boundaries. After accounting for these effects and adjusting rates for the influence of the short (29-106 yr) data record, within each category the typical observed variation is about an order of magnitude. We estimate seismic coupling coefficients, that is, the proportions of plate tectonic slip accommodated as earthquake rupture and reflected in the moment rates. Coupling may be 0.7 or greater along shallow convergent boundaries where at least one plate is continental. For all other boundary categories coupling is generally less than 0.4; it is 0.2 or less along most divergent boundaries and for intermediate and deep boundaries at depths exceeding 100 km. These results confirm that there are fundamental mechanical differences in the failure processes acting along different categories of plate boundaries. One implication is that only along a few highly coupled boundaries is it plausible that analysis of seismicity alone might lead to successful algorithms to predict large earthquakes.

Dependence of seismic coupling on normal fault style along the Northern Mid‐Atlantic Ridge

“…These values are in agreement with independent estimates from the global CMT catalog, which yielded 0.23-0.82×10 15 J/yr/km for the entire portion of the MAR separating the North American and African plates [Frohlich and Wetzel, 2007].…”

“…Cowie et al [1993] later argued that seismic slip had to represent an insignificant fraction (<1%) of the time-averaged fault slip rate at the fast-spreading East Pacific Rise. Subsequent studies documented an exponential decrease in seismic moment release rates, and thus seismically accommodated strain, between slow and fast spreading centers [Sobolev and Rundquist, 1999;Rundquist and Sobolev, 2002;Bird et al, 2002;Frohlich and Wetzel, 2007]. This article is protected by copyright.…”

Scaling relations for seismic cycles on mid‐ocean ridge transform faults

“…By contrast to slip on continental strike‐slip faults, slip on mid‐ocean ridge transform faults (RTFs) is largely aseismic [e.g., Brune , 1968; Bird et al , 2002; Boettcher and Jordan , 2004; Frohlich and Wetzel , 2007] and magnitudes of the largest earthquakes are small (6 ≤ M W ≤ 7.1) compared to the large RTF areas [e.g., Bird et al , 2002; Boettcher and Jordan , 2004]. Seismicity on RTFs is known to follow a tapered frequency‐moment distribution [e.g., Kagan and Jackson , 2000], where N 0 is the cumulative number of events above the completeness threshold moment M 0 and β is the slope of the distribution below the exponential roll off at M C , which is the seismic moment of the largest expected earthquake.…”

Spatio-temporal distribution of seismic moment release near the source area of the 2011 Tohoku-Oki earthquake

“…Another is that summed moment release rates are sensitive to the assumed width of seismically-active zones (Sandiford, 2008). Several improvements have been proposed to remedy the above limitations (McCaffrey, 1997;Frohlich, 2007;Frohlich and Wetzel, 2007); however, the computation procedure still seems a little complicated.…”