Untangling tectonic slip from the potentially misleading effects of landform geometry

Abstract

We present a new three-dimensional (3D) approach to the analysis of fault scarps using high-resolution elevation models. Advances in topographic measurement techniques [e.g., lidar (light detection and ranging) and photogrammetric techniques] have allowed extensive measurement of single earthquake and cumulative scarps to draw conclusions about along-strike slip variation and fault slip history. The resulting slip distributions are almost always variable and noisy, but the cause is often unclear. We first present the results of sensitivity analysis to demonstrate significant apparent noise due to varying terrain and fault and measurement geometry (topographic slope attitude, fault dip and slip obliquity). We show, with a case study on the Hoshab fault, Pakistan, that oblique slip can have a significant effect on the measured apparent slip. Individual planar geomorphic markers only constrain one component of the full 3D slip vector. We use the variation in apparent offset with marker geometry to constrain the slip vector in 3D. Combining multiple offset measurements along strike, we show that determining the slip vector is reduced to a simple linear formulation. We test our method using a terrestrial lidar data set from the ruptures on the Borrego fault from the 2010 El Mayor-Cucapah earthquake (Baja California, Mexico). Combining 22 observations, we estimate a throw of 1.56 ± 0.02 m and a lateral slip of 1.9 ± 0.3 m. The vertical slip estimate agrees well with previous studies, but the lateral slip is significantly smaller. In regions of steep varied topography or with oblique slip, our method will give enhanced slip resolution while standard methods will give biased estimates.

Active Tectonics Around Almaty and along the Zailisky Alatau Rangefront

“…Surveys of the present‐day streambeds showed that the post‐depositional tilt of the fitted surfaces is negligible. The geometrical error introduced by the landform geometry in the sense of Mackenzie and Elliott () also does not affect our results significantly beyond the noted 10% uncertainties.…”

Controls on Early‐Rift Geometry: New Perspectives From the Bilila‐Mtakataka Fault, Malawi

“…As no fault plane slip direction indicators were found, we assume that the faults are purely normal (Chorowicz & Sorlien, ; Jackson & Blenkinsop, ). Under this assumption the scarp height may be used to represent the surface displacement (Morley, ), except where the scarp trend varies considerably from the average trend (Mackenzie & Elliott, ). Relative to the fault length, the average vertical surface displacement (∼14 m) is greater than would be expected by a single earthquake event (∼6 m; Scholz, ), but the maximum surface displacement (∼28 m) is significantly less than expected for the total displacement (∼1,000 m; Kim & Sanderson, ).…”

“3D_Fault_Offsets,” a Matlab Code to Automatically Measure Lateral and Vertical Fault Offsets in Topographic Data: Application to San Andreas, Owens Valley, and Hope Faults

“…Several sources of errors are revealed. The first is related to a possible incorrect identification of the two marker sections to be paired (e.g., Mackenzie & Elliott, ; Scharer et al, ; Zielke et al, ). The expertise of the user is here fundamental and irreplaceable.…”

“…More recently, the explosion of high‐resolution topographic data, especially Lidar that allows the measurement of the bare Earth surface at ≤1 m resolution (e.g., Arrowsmith & Zielke, ; Bevis et al, ; De Pascale et al, ; Frankel et al, ; Haddad et al, ; Lin et al, ; Meigs, ; Zielke et al, ; Zielke et al, ), has motivated the development of new, automatized approaches to remotely measure fault slips in the topographic data. These approaches, so far, use an overall measure of the topography (Billant et al, ), planar surfaces (Mackenzie & Elliott, ), or linear geomorphic features (Haddon et al, ; Zielke et al, ; Zielke & Arrowsmith, ) as recorders and markers of the fault displacements. In particular, Zielke and Arrowsmith () and Zielke et al () have developed a Matlab code, LaDiCaoz (updated version, LaDiCaoz_v2, released by Haddon et al, ), to semiautomatically measure fault offsets across ubiquitous linear geomorphic features such as stream channels and terrace risers.…”