Coseismic slip variation assessed from terrestrial lidar scans of the El Mayor-Cucapah surface rupture

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• 作者：Peter O. Gold^a ; ^{peter.gold@utexas.edu} ; Michael E. Oskin^a ; Austin J. Elliott^a ; Alejandro Hinojosa-Corona^b ; Michael H. Taylor^c ; Oliver Kreylos^a ; Eric Cowgill^a
• 关键词：terrestrial lidar scanning ; slip distribution ; El Mayor&ndash ; Cucapah ; earthquake rupture ; measurement uncertainty ; slip variation
• 刊名：Earth and Planetary Science Letters
• 出版年：2013
• 出版时间：15 March, 2013
• 年：2013
• 卷：366
• 期：Complete
• 页码：151-162
• 全文大小：2496 K

文摘

We analyze high-resolution (>10³ points/m²) terrestrial lidar surveys of the 4 April 2010 El Mayor-Cucapah earthquake rupture (Baja California, Mexico), collected at three sites 12-18 days after the event. Using point cloud-based tools in an immersive visualization environment, we quantify coseismic fault slip for hundreds of meters along strike and construct densely constrained along-strike slip distributions from measurements of offset landforms. Uncertainty bounds for each offset, determined empirically by repeatedly measuring offsets at each site sequentially, illuminate measurement uncertainties that are difficult to quantify in the field. These uncertainties are used to define length scales over which variability in slip distributions may be assumed to reflect either recognizable earthquake mechanisms or measurement noise. At two sites characterized by 2-3 m of concentrated right-oblique slip, repeat measurements yield 2¦Ò uncertainties of ¡À11-12 % . Each site encompasses ¡«200 m along strike, and a smoothed linear slip gradient satisfies all measurement distributions, implying along-fault strains of ¡«10^?3. Conversely, the common practice of defining the slip curve by the local slip maxima distorts the curve, overestimates along-fault strain, and may overestimate actual fault slip by favoring measurements with large, positive, uncertainties. At a third site characterized by 1-2.5 m of diffuse normal slip, repeat measurements of fault throw summed along fault-perpendicular profiles yield 2¦Ò uncertainties of ¡À17 % . Here, a low order polynomial fit through the measurement averages best approximates surface slip. However independent measurements of off-fault strain accommodated by hanging wall flexure suggest that over the ¡«200 m length of this site, a linear interpolation through the average values for the slip maxima at either end of this site most accurately represents subsurface displacement. In aggregate, these datasets show that given uncertainties of greater than ¡À11 % (2¦Ò), slip distributions over shorter scales are likely to be less uneven than those derived from a single set of field- or lidar-based measurements. This suggests that the relatively smooth slip curves we obtain over ¡«10² m distances reflect real physical phenomena, whereas short wavelength variability over ¡«10⁰-10¹ m distances can be attributed to measurement uncertainty.