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Global frequency of magnitude 9 earthquakes

¹ GNS Science, PO Box 30368, Lower Hutt, New Zealand

View larger version (34K): [in this window] [in a new window]   Figure 1. Map of world's major subduction zones (thick gray lines) and tectonic plate boundaries (Bird, 2003). Filled circles show locations of known earthquakes of Mw 7.5 or greater since 1900 (circle radius and grayscaled by magnitude). Open circles are largest known earthquakes from A.D. 1700 to 1900 (compiled by Stein and Okal, 2007). Arrows show horizontal velocity of subducting plate relative to overriding plate. Dates are given for all M9 quakes.

View larger version (18K): [in this window] [in a new window]   Figure 2. Simulations of recurrence time T estimates from 5000 Monte Carlo histories of observations of duration H. When H/T < 5, recurrence time is poorly estimated (low scatter in T is due to small number of events when H/T is small). At high H/T, recurrence time is on average recovered but scatter in estimated T remains large. Obtaining T with high confidence (low T) requires H >> T.

View larger version (24K): [in this window] [in a new window]   Figure 3. Plot of the difference between Mw of predicted largest earthquake and observed largest earthquake versus predicted recurrence time for such quakes at each subduction zone segment. Dots represent post-1900 quakes only, while open circles are post-1700 (from Stein and Okal, 2007). Gray area shows where Mw difference is <0.4 magnitude units (error level in estimates).

View larger version (24K): [in this window] [in a new window]   Figure 4. Histograms of the probability that number of (N) M9 earthquakes will occur randomly in any 100 yr period, given distribution of expected recurrence times at 32 subduction zone segments. Curves are labeled by values used in simulation (T is recurrence time; P = probability of an event during any year, f = fraction of moment that occurs in largest earthquake; value of , the fraction of total slip released by earthquakes, is 1.0 for all simulations). Simulations with "f = 1 – β" use β values from individual subduction zones estimated by Kagan (1999) and simulation 5 randomly samples β values. Simulation 6 simulates subset of 22 subduction zones based on age younger than 90 Ma that can produce M9 earthquakes. All simulations except 7 use Poisson probability for M9 occurrence (P = 1/T); for simulation 7, P increases linearly with time t since last event.