Complex ruptures in the historical record, illuminated by photogrammetric topography and analog seismograms

Austin J. Elliott, Richard T. Walker, Barry E. Parsons, Galina Kulikova, Christoph Grützner, Kanatbek Abdrakhmatov, Zhuqi Zhang, & Zhikun Ren

Published August 14, 2019, SCEC Contribution #9560, 2019 SCEC Annual Meeting Poster #118

Although contemporary earthquakes continue to surprise us with their complexity, violating expectations about rupture length, geometry, and fault involvement, rupture complexity is not a new phenomenon. We simply have not previously had the tools to investigate earthquakes in the detail that is now possible. We use newly developed tools in photogrammetric geomorphology and digital seismology to re-visit earthquake ruptures that occurred nearer the turn of the last century and interrogate these further examples of large, multi-fault ruptures within the continental crust. We map and measure the surface traces of the 1889 M8.3 Chilik earthquake in southern Kazakhstan/Kyrgyzstan and the 1932 M7.6 Changma earthquake in western China, to show that each of them ruptured an array of faults that would not necessarily have been expected to fail together in a single earthquake (for example when considering fault branching rules & stepover constraints in models like UCERF). With surface ruptures documented in detail, we digitize and analyze the early analog teleseismic waveforms of these events to better understand their rupture processes. The Chilik event ruptured three conjugate left- and right-lateral faults within a compressional regime, which meet at <45° angles. The Changma rupture jumped along a set of reverse and left-lateral faults separated by numerous bends and substantial steps, yet our measurements show that the highly variable fault geometry remains compatible with a single slip vector. With contemporary questions about rupture propagation in mind, it is valuable to add to our repository of knowledge about earthquake ruptures using earlier cases that we can still/now document. These two cases illustrate that single event ruptures a) may propagate along faults with different senses of motion that meet at extremely acute angles and b) may jump along an array of surficially separated faults with different kinematics to form a major single event.

Key Words
rupture propagation, photogrammetry, coseismic slip, analog seismology, historical earthquakes

Citation
Elliott, A. J., Walker, R. T., Parsons, B. E., Kulikova, G., Grützner, C., Abdrakhmatov, K., Zhang, Z., & Ren, Z. (2019, 08). Complex ruptures in the historical record, illuminated by photogrammetric topography and analog seismograms. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology