Seismicity along Subduction Zones: Visualization with a Physical Basis

It is a common practice to plot epicenters and hypocenters as symbols of equal sizes on maps and cross-sections. While this representation is effective in relating seismicity to high-angle faults, it lacks a physical basis because equal weights are assigned to events that span several orders of magnitude in seismic moment. Furthermore, for cases such as subducted lithosphere where seismicity does not occur along major, through-going faults, "connecting the dots" leads to erroneous impressions of true seismogenic structures. Another common practice is to plot each event according to its magnitude. In principle, this preserves the size of earthquakes by using the logarithmic magnitude scale. The results, however, are not intuitive and the physical meaning of the magnitude scale is unclear. In contrast, we use simple scaling laws between fault area and seismic moment to plot seismicity in a way that conforms to the true scale of maps and cross-sections. The results are intuitive and often quite distinct from plots produced from common practices. We will illustrate the utility of our approach with examples from several different tectonic settings, including the large (Mw 7.6 and 7.7) August 19, 2002 Tonga deep earthquakes, configurations of sub-horizontal outboard earthquakes and complex Wadati-Benioff zones [Chen and Brudzinski, Science, v. 292, p. 2475, 2001], aftershock productivity of deep earthquakes [Wu and Chen, GRL, v. 26, p. 1977, 1999], and dual, out-of-sequence thrusts at mid- to lower-crustal depths [Kao and Chen, Science, v. 288, p. 2346, 2000].