Wenjun Zheng

Using an unmanned aerial vehicle for topography mapping of the fault zone based on structure from motion photogrammetry

ABSTRACT High-precision and high-resolution topography is the basis of the quantitative study of active faults. Light detection and ranging (lidar) is currently the most popular method for obtaining such data, but its relatively high cost greatly limits its use in many geoscience applications. Recently, with the rapid development of computer vision science and the growing application of small unmanned aerial vehicles (UAVs), Structure from Motion (SfM) photogrammetry shows great potential for providing topographic information of comparable resolution and precision to lidar surveys, but at significantly lower cost. In this study, we examined the applicability of SfM photogrammetry in modelling the topography of the fault zone using images acquired with a low-cost digital camera mounted on a UAV over the Haiyuan fault. The resolution and accuracy of the SfM-derived topography were evaluated in detail using existing airborne lidar data as a benchmark. The results show that the density of the point cloud generated by SfM photogrammetry is nearly 70 times higher than that from the airborne lidar. Furthermore, considering the errors in the lidar data itself, the precision of the SfM point cloud is comparable to that of the lidar point cloud. Overall, our results demonstrate that the UAV-based SfM photogrammetry method can provide an inexpensive, effective, and flexible alternative to airborne lidar for the topography mapping of the fault zone.

Validation of SMAP Soil Moisture analysis product using in-situ measurements over the Little Washita Watershed

Soil moisture is a key state variable which plays a significant role in many hydrological processes. The Soil Moisture Active Passive (SMAP) mission was launched on 31 January 2015 which can provide global information of soil moisture. Among the released SMAP data sets, the Level 4 Surface and Root Zone Soil Moisture Analysis Product (L4_SM) can not only provide information on surface soil moisture (top 5 cm of the soil column), but also provide estimates of root zone soil moisture (top 1 m of the soil column) which is very important for several key applications targeted by SMAP. However, since this product has been released only for a short time, its accuracy and reliability has not been validated so far. In this study, we evaluated the L4_SM soil moisture analysis product against in-situ soil moisture measurements collected from the Little Washita Watershed network located in southwest Oklahoma in the Great Plains region of the United States. The results show that both the surface and root zone soil moisture estimates in the L4_SM product are in good agreement with the in-situ measurements, and the RMSE is 0.027 m3/m3 and 0.032 m3/m3 for the surface and root zone soil moisture respectively which both have exceeded the RMSE requirement of 0.04 m3/m3 for this product.

Active Bending‐Moment Faulting: Geomorphic Expression, Controlling Conditions, Accommodation of Fold Deformation

Bending-moment faults and flexural-slip faults (FSFs), as two basic fault styles due to bending-related tangential longitudinal strain, extensively and prominently crop out as surface scarps in the Pamir-western Kunlun and southern Tian Shan regions, northwestern China. Characteristic geomorphic expression, favorable formation conditions, and the role in folding accommodation of active FSFs have been systematically summarized in our recent studies. Here we investigate similar properties for well-developed bending-moment normal fault (BMnF) scarps at four sites. Our study concludes the following: (i) BMnF scarps are relatively sinuous compared to FSF scarps and probably trend obliquely to the fold hinge. A group of BMnF scarps can delineate a single asymmetric graben or create grabens alternating with horsts. (ii) BMnF scarps primarily overlie poorly-layered conglomerates. The fold’s interlimb angle can range from ~160° to <40°, and the folding kinematics can vary from active-hinge migration to fixed-hinge rotation. (iii) The fault-zone width, fault spacing, and efficiency in folding accommodation significantly decrease with (a) thinner conglomerate beds, (b) a smaller interlimb angle, and (c) the transition of the hinge frommigrated to fixed. (iv) Different bed lithologies and fold geometries beneath the surface account for the predominance of BMnF scarps on the western Kunlun piedmont and FSF scarps in the Pamir-Tian Shan convergent zone. (v) Presence of BMnF scarps on the western Kunlun piedmont indicates that ~4 km of fault slip is transferred northward along a detachment at the base of the Cenozoic and is ultimately absorbed by the Mazatagh Thrust in the Tarim Basin.

Climatically driven formation of the Tangxian planation surface in North China: An example from northwestern Zhongtiao Shan of the Shanxi Graben System

The development of planation surfaces requires stable tectonic and climatic conditions. However, it is difficult to discuss in detail how tectonic movement and/or climate change affects erosion, deposition, and uplift associated with the development, formation, and disintegration of planation surface. This article presents a case study on the development and formation of the Tangxian planation surface (TXPS) by establishing the magnetostratigraphy of one piedmont deposition section related to planation, and combining the depositional sequence overlying TXPS and basin sediments. Further, we discuss the role of tectonics and climate change in the geomorphic evolution of the TXPS during the late Cenozoic and revise the final formation age to be ca. 3.1 Ma by the relative deposition process. The vertical rates of the main fault constrained by different geomorphic surfaces and stable deposition in the basin show stable and moderate tectonic activity in the study area since the Pliocene, and a series of sedimentary records reveal that the climate in North China was stably warmhumid from the late Miocene to early Pliocene. Stable tectonic activity and stable climate were important bases for pediment development; however, abrupt climatic changes during the late Pliocene might be the main driving force of the final formation of the TXPS in North China. LITHOSPHERE; v. 10; no. 4; p. 530–544 | Published online 16 May 2018 https://doi.org/10.1130/L720.1

Constraining the Distribution of Vertical Slip on the South Heli Shan Fault (Northeastern Tibet) From High‐Resolution Topographic Data

Reconstruction of the along-fault slip distribution provides an insight into the long-term rupture patterns of a fault, thereby enabling more accurate assessment of its future behavior. The increasing wealth of high-resolution topographic data, such as LiDAR and photogrammetric DEMs, allows us to better constrain the slip distribution, thus greatly improving our understanding of fault behavior. The South Heli Shan Fault is a major active fault on the northeastern margin of the Tibetan Plateau. In this study, we built a 2-m resolution DEM of the South Heli Shan Fault based on high-resolution GeoEye-1 stereo satellite imagery, and then measured 302 vertical displacements along the fault, which increased the measurement density of previous field surveys by a factor of nearly 5. The cumulative displacements show an asymmetric distribution along the fault, comprising three major segments. An increasing trend from west to east indicates that the fault has likely propagated westwards over its lifetime. The topographic relief of Heli Shan shows an asymmetry similar to the measured cumulative slip distribution, suggesting that the uplift of Heli Shan may result mainly from the long-term activity of the South Heli Shan Fault. Furthermore, the cumulative displacements divide into discrete clusters along the fault, indicating that the fault has ruptured in several large earthquakes. By constraining the slip-length distribution of each rupture, we found that the events do not support a characteristic recurrence model for the fault.

Modeling the topography of fault zone based on structure from motion photogrammetry

The quantitative study of active faults is highly dependent on high-precision and high-resolution topographic data. Though Light Detection and Ranging (LiDAR) technology can provide such data, its high cost greatly limits its use in many geoscience applications. Recently, the Structure from Motion (SfM) photogrammetry shows a great potential to provide topographic information with high precision, but at significantly lower costs than the laser scanning survey. In this study, the applicability of SfM photogrammetry method in modeling the topography of fault zone was investigated by using images acquired with a low-cost digital camera mounted on an UAV. The resolution and accuracy of the SfM-derived topographic data was evaluated in detail using existing airborne LiDAR data as a benchmark. The results show that the SfM photogrammetry method can produce a point cloud with the density seventy times higher than the airborne LiDAR. Furthermore, considering the errors in LiDAR data itself, and the precision of the SfM-derived point cloud is comparable to that of the LiDAR point cloud, demonstrating that the SfM photogrammetry method is an inexpensive and effective alternative to airborne LiDAR for the topography modeling of fault zone.