Location of Active Faults using Geomorphic Indices in Eroded Landscapes, South Taranaki, New Zealand

<p>South Taranaki region has a number of active faults that show surface expression in the younger and harder materials near the coast and central volcanoes of the North Island, but these traces finish abruptly inland when they cross into older, heavily eroded, mudstone and sandstone. Current methods to locate surface evidence of active faults (i.e. geomorphic interpretation of stereographic aerial photography) are not fully successful in this region. Erosion occurs here at a greater rate than surface rupture of faults which causes the removal of surface expression, and/or dense tree cover obscures surface expression. International studies of tectonic activity in eroded landscapes have identified geomorphic indices as useful reconnaissance tools to locate active faults. This research applies geomorphic indices to the Taranaki region for the first time. Four indices are tested; stream length-gradient index, stream channel sinuosity, hypsometry and drainage basin asymmetry. Results are obtained by applying the indices to four freely available national Digital Elevation Models (DEMs) of differing resolutions. This allowed comparison between DEMs, providing the ability to test DEM quality and at what scale geomorphic indices could be applied to these freely available data. Results show that the geomorphic indices used can identify changes to the equilibrium state at a catchment and stream channel scales. However, the myriad of physical processes occurring at a range of temporal scales within this area make identification of a tectonic signature a challenging task. Conclusive examples of tectonic processes are evident and analysis suggests that these examples are likely to be due to recent or large fault ruptures. There are many areas where a tectonic influence to the equilibrium state of a stream or catchment can be inferred. These areas could then be targeted for detailed geophysical or ground based geological studies. Furthermore, the comparison of results from the four DEMs highlights a range of issues with DEM collection methods and resolution. This study concludes that geomorphic indices can provide an effective method to locate evidence of recent and large faulting events. However, this type of analysis is hindered by the resolution of available digital elevation data.</p>

Location of Active Faults using Geomorphic Indices in Eroded Landscapes, South Taranaki, New Zealand

<p>South Taranaki region has a number of active faults that show surface expression in the younger and harder materials near the coast and central volcanoes of the North Island, but these traces finish abruptly inland when they cross into older, heavily eroded, mudstone and sandstone. Current methods to locate surface evidence of active faults (i.e. geomorphic interpretation of stereographic aerial photography) are not fully successful in this region. Erosion occurs here at a greater rate than surface rupture of faults which causes the removal of surface expression, and/or dense tree cover obscures surface expression. International studies of tectonic activity in eroded landscapes have identified geomorphic indices as useful reconnaissance tools to locate active faults. This research applies geomorphic indices to the Taranaki region for the first time. Four indices are tested; stream length-gradient index, stream channel sinuosity, hypsometry and drainage basin asymmetry. Results are obtained by applying the indices to four freely available national Digital Elevation Models (DEMs) of differing resolutions. This allowed comparison between DEMs, providing the ability to test DEM quality and at what scale geomorphic indices could be applied to these freely available data. Results show that the geomorphic indices used can identify changes to the equilibrium state at a catchment and stream channel scales. However, the myriad of physical processes occurring at a range of temporal scales within this area make identification of a tectonic signature a challenging task. Conclusive examples of tectonic processes are evident and analysis suggests that these examples are likely to be due to recent or large fault ruptures. There are many areas where a tectonic influence to the equilibrium state of a stream or catchment can be inferred. These areas could then be targeted for detailed geophysical or ground based geological studies. Furthermore, the comparison of results from the four DEMs highlights a range of issues with DEM collection methods and resolution. This study concludes that geomorphic indices can provide an effective method to locate evidence of recent and large faulting events. However, this type of analysis is hindered by the resolution of available digital elevation data.</p>

Using morphometric and geomorphic indices to assess Western São Francisco Craton neotectonic traces

Recently, geomorphometric properties of river networks and catchments have been described and applied as an efficient tool in the investigation of the landforms' response to neotectonics. Geometric parameters of the Cotovelo River catchment extracted from an Alos-Palsar digital elevation model were used to compute morphometric and geomorphic indices to investigate whether the bedrock structure and recent active tectonics influence the local drainage network. The Cotovelo catchment is situated in the Middle to Upper Proterozoic western foreland basin of the São Francisco craton, in northwestern Minas Gerais, Southeastern Brazil; it is presumed to be a stable piece of earth’s crust. The automatically generated streams were processed at the sub-catchment scale to calculate the hypsometric integral, relief ratio, stream frequency, and drainage density morphometric indices as well as supported a geomorphic study based on the basin shape, asymmetry factor, valley floor width-to-height ratio, mountain front sinuosity, transverse topographic symmetry factor, and stream-length gradient index. Achieved results revealed recent and low-rate tectonic activity and structural control on the fluvial morphology. Prominent knickpoints, aligned with mapped fault scarps, disclose straight erosive fronts away from stratigraphic borders, indicating these features are unrelated to lithological changes. Despite the catchment location, the area exhibits impressive fluvial anomalies, and dissection occurs preferentially along ancient faults and fractures densely occurring in the rocky strata. Channel parallelism in context of medium to high relief and steep slopes, remarkably structurally drive fluvial dissection, asymmetric and elongated drainage catchments, and aligned landforms suggest neotectonic influence on the drainage network.

Geological Lineament Pattern and Geomorphic Indices Characteristic Related To Geothermal Manifestation Appearance: A Case Study from Gunung Talang District and Its Surroundings, Solok Regency, West Sumatra Province, Indonesia

The study area is located in Gunung Talang District and its surroundings, Solok Regency, West Sumatra Province, Indonesia. This area has a potential volcanic geothermal system and is generally covered by the Quarternary rocks which are deformed due to the tectonic activity of the Sumatran Fault System. Geological structure traces are not well preserved in such an area. This study aims to determine the geological lineament pattern associated with geological structure, the geomorphic indices characteristic related to the tectonic activity and rock permeability, and the geothermal manifestation appearance based on these two factors. Geological lineament pattern is identified using the remote sensing method. Geomorphic indices characteristic is calculated through the quantitative analysis of bifurcation ratio (Rb), drainage density (Dd), mountain front sinuosity (Smf), and lineament density (Ld). Geothermal manifestation appearance is evaluated through geospatial analysis using the overlay method on the geological lineament pattern and the geomorphic indices characteristic, which are then correlated with the distribution of geothermal manifestations. The main geological lineament patterns associated with the geological structures in the study area are north-northwest–south-southeast (NNW-SSE) and northeast-southwest (NE-SW). These lineament patterns indicate synthetic and antithetic strike-slip faults around the Sumani Segment of Sumatran Fault System successively. The geomorphic indices characteristics imply deformed areas (Rb values: 1.14-5.45), rough (Dd values: 2.00-2.66 km/km2), moderate (Dd values: 3.14-4.00 km/km2), and slightly fine landform textures (Dd values: 4.32-5.51 km/km2), active (Smf values: 1.05-1.64) and moderate to slightly active tectonisms (Smf values: 1.74-2.52), low (Ld values: 0.00-0.84 km-1), moderate (Ld values: 0.84-1.68 km-1), and high lineament densities (Ld values: 1.68-2.52 km-1) over the study area. The geothermal manifestations in the study area are divided into four groups based on their appearance characteristics, namely group I (Songsang and Garara hot springs), group II (Padang Damar, Bukit Gadang, and Batu Bajanjang hot springs), group III (Bukit Kili and Bawah Gunuang hot springs), and group IV (Gabuo Atas and Bawah Betung hot springs).