Tectonic and lithologic controls on the landscape adjustment along the eastern terrain of the Mae Tha fault, northern Thailand

uniform lithology. Our study highlights the use of topographic adjustment as one of the efficient tools to describe the dynamics of active deformation on the landscape over space and time. According to the mutual analysis, our finding suggests that lithologic resistance and spatial differences in fault lineaments ultimately control characters of channel profiles and overall landscape topography.


INTRODUCTION
Landforms in tectonically active settings are the product of an interaction between tectonics, climatically- Dietrich et al., 2003;Whipple, 2009;et al., 2008). Such an interaction governs topography and topographic relief as tectonics acts to change regional surface elevations processes and sediment transport along topographic governing rates and patterns of landscape responses to DiBiase et al., 2015;Schmidt and Montgomery, 1995). Understanding these factors that control spatial changes on erosional landscapes remains a To measure the deformation due to tectonic processes, an exposure of a piercing point or a linear/planar on an alluvial fan or traces of active faults. The difference between pre-deformational geometry and the presently offset features can inform about tectonic and climatic shifts 2012). However, the preservation of geomorphic features is poor when they are old and/or exposed to extreme Howard et al., 1994;;Hilley et al., 2019), transmit signals of changes throughout a landscape via Kirby and Whipple, 2012; ; Wobus et al., 2006 adjacent hillslopes. The responses of hillslopes always lag Hurst et al., 2012Kirby et al., 2003, 2007Kirby and Whipple, 2001 to describe active deformation on the landscape has been successful in several active mountain belts worldwide Kirby et al., 2003Kirby et al., , 2007Kirby and Whipple, 2001). Howard et al., 1994;Snyder et al., 2003; ), we hypothesize that the Duvall et al., 2004;Kirby et al., 2003 the steepness becomes a more effective agent of channel Wobus et al., 2006 controls channel steepness and presumably dictates Hurst et al., 2019;Kirby et al., 2003Kirby et al., , 2007.
Although tectonic processes and lithology worldwide have been extensively mapped, we still need insight into how tectonics and lithology govern landscape changes over space and time. A single discovery does not apply everywhere on the Earth. An understanding of the factors that control various geological sites can provide more information about the dynamic deformation of landscapes.
of active deformation on a landscape from channel in channel morphology and assess the manner in which tectonic and lithologic factors control the adjustment of

Overview of bedrock incision model
E, is a power-law function of contributing drainage area, A proxy for local channel discharge) and channel gradient, S Howard et al., 1994;;2004 E= KA m S n substrate-, climate-, geometric-, and hydrologic-dependent variables, and m and n are exponents related to geometry, Howard et al., 1994; ; Whipple et al., 2000). The evolution channel bed elevation U, and channel erosion rate, E where x is the location and t is the time. Under a steady-state condition Ss, is expressed as: rewritten as: where K s and is the rate of change of local channel gradient relative Flint, 1974;Wobus et al., 2006). K s and are channel steepness and channel concavity indices, respectively. The channel steepness index, K s , U, and erosional K, can be described as: K s , is affected by U, K and n U, depends on the change of channel bed elevation through time, K, amalgamates factors DiBiase and Whipple, 2011;Lague et al., 2005;Snyder et al., 2003; ). The slope exponent, n, is assigned to the 1999; Whipple et al., 2000). more erodible, precipitation is promoted, and sediment 2010 model to explain the response of channel morphology and landscape topography to variations in lithologic and tectonic forcing where climatic conditions are relatively uniform.

Study site: Mae Tha fault in Chiang Mai and Lamphun provinces
The study site is located along the eastern side of Chiang watersheds: Mae Ngat and Mae Khot rivers, Mae Kuang and Mae On rivers, and Mae Tha river, feed to Chiang Mai Fig. 1A). The direction of rivers in these watersheds follows the different orientations of the Mae The MTFZ, composed of 52 fault segments, cuts MTFZ, high terrain in the northern zone is intruded by Charusiri et al., 1993). The lower parts of the terrain are mantled by Carboniferous massive sandstone interbedded with siltstone and shale of the Mae Tha group and Silurian-Devonian low-to-medium Fig. 1B et al., 2020). The climatic condition across this region is a tropical June and October, while the rest of the year is hot summer and cool winter. The mean annual accumulated rainfall ranges between 1100 and 1300mmyr -1 over the period  , moreover, landform evolution is between the youthful stage and the mature stage because the rugged terrain is typically Fig. 2C).
The MTF is considered a moderate-to-high active fault Department of Mineral Resources, 2020; ). According to the study of age of sediment samples in trench sites where the MTF Fig. 3), the study reveals at least four times 5,000, and 1,500 years ago. The slip rate of the MTF is estimated as 0.1-1mmyr -1 . The recurrence interval of large Department of Mineral Resources, 2008Resources, , 2018. Furthermore, geomorphic The development of channels and landscape topography tectonic and litho-structural control, apparently little rainfall of the area compared to regional climatic gradients across Northern Thailand.

Analysis of geomorphic indices on channels
To investigate the spatial variation in channel the channel bed along the entire course of the channel), contributing drainage areas, and channel gradients. These data are used to calculate variations in geomorphic indices  Figure 1B-D represents the relatively constant elevation in the northern and central zones and the decrease in elevation toward the south. Maximum, mean and minimum elevation extracted from a 15km wide swath profile ( Fig. 2A). C) High topographic relief across the study site corresponds to the variation in elevation profile (Fig. 2B). Transverse Hypsometric Integral (THI) is approximately 0.5, implying that the age of the landscape evolution is between the youthful stage to maturity. Abbreviations and symbols in Figure

Extraction of longitudinal channel profiles
collected and produced by Synthetic Aperture Radar from the Laurencelle, et al., 2015). The DEM has proceeded through Radiometric pixels and improve the resolution. We extracted 35 lower-order watersheds along the eastern terrain of the MTF. These

K s
). We regressed a log-log plot of local channel gradients against upstream drainage areas, following the approach of Wobus et al.
To spatially compare channel steepness among different channel segments of varying upstream drainage areas and concavity index, a suite of normalized channel steepness k sn ref Wobus et al., 2006). Normalized channel steepness indices could be calculated as The difference in k sn does not depend on ref compares k sn for channels with different upstream drainage Duvall et al., 2004;Howard et al., 1994;Kirby and Whipple, 2012;Snyder et al., 2003).

Analysis of lineaments: faults and fractures
The MTF generates moderate-to-high seismic activities. determined the fracture density -an evaluation of lineament density generated by the connection between faults and fractures. We used aerial and satellite images provided by all lineaments and infer the impact of different levels of tectonic forcing across the landscape.

Characterization of structures and fracture density
broad, we could not observe smaller lineaments on digital images and DEM because forest is densely populated. The Because of the recent advances in high-resolution digital topographic data providing a more accurate description of landscape features, fractures in the landscape can be the landscape from the theory that rectangular drainage rectangular patterns of bedding planes, faults, and fractures Howard, 1967;Mejia and Niemann, 2008).
To compare the spatial distribution of fractures across the region, we assigned weights to different magnitudes of each lineament: the MTF was assigned a weight of 3, minor faults were given a weight of 2, inferred fractures were assigned a weight of 1, and a weight of 0 was given to other areas that are not associated with any lineaments Table 1). We calculated the fracture density as the ratio of Geomorphic controls on Mae Tha fault's eastern terrain 11 a maximum height of 90m above the ground.

Characterization of sediment particles
We surveyed eight channels from north to south to generate an extensive dataset of their grain size distribution Fig. 7). For each channel, we started at the intersection of the trace of the MTF and channel route and surveyed approximately 100m upstream. The selection of channels was planned to survey channels with a wide range of channel steepness indices.
We used the Wolman pebble count procedure to characterize sediment grain size distribution as we measured the sizes of random particles using the United States Fig. 7B-C). We randomly collected a minimum of 100 sediment particles using a zigzag pattern across the surveyed channels 5, 7, ). The collection of e.g. D 10 , D 50 and D 90 size reduction was minimal in lower-order channels. The the whole drainage area.

Spatial variations in channel steepness indices
spatial variations in channel gradients and channel steepness indices along the eastern terrain of the MTF. Less than half   Table 2 represents the variation in topographic  o l o g i c a A c t a , 2 1 . 4 , 1 -2 2 ( 2 0 2 3 o l o g i c a A c t a , 2 1 . 4 , 1 -2 2 ( 2 0 2 3  Red dots represent knickpoints that mark the boundary between channel segments with different k sn . B) Variations in normalized channel steepness indices (k sn ). Oranges dots represent normalized channel steepness indices on channel segments above knickpoints, while blues dots represent normalized channel steepness indices on channel segments below knickpoints. The red and yellow stars indicate the highest k sn value at channel 4 and the lowest k sn value at channel 35, respectively. C) Channel concavity ( ) as a function of distance from the northern tip of the segment. D) The elevation of knickpoints from north to south ranges between 450 and 900m with a regional mean of 650m.
reasonable with the degree of uncertainty in the data. For ), the channel reaches above r 2 = 0.21), despite the reduction of k sn Fig. 9C).
k sn in the northern zone. These channels typically exhibit steeper the average k sn at >100m 0.9 , while the average k sn below 0.9 between 450 and 900m above sea level with a regional mean Fig. 9D disappears along channels toward the south.
Despite the low standard range of r 2 in these k sn and values, the results primarily represent the spatial variations in normalized channel gradients and steepness. We used them to interpret the history of uplift and channel incision across the region.

Spatial variations in fracture density
The MTF is considered moderate-to-high seismic activities close to the MTF may experience high levels of damage and generate a cluster of fractures relative to a distant region to the MTF. As a result, we characterize the different levels of Fig. 10A The detailed map of lineaments yields the spatial variation in fracture density across the landscape. We categorize the Fig. 10B). Generally, the high level of fracture density distributes along the trace of the MTF. The values of fracture density decline toward the distant regions from the active major and minor faults. According to Figure 10B, the low level of fracture density distributes along the western side of the MTF. Along the eastern terrain of the MTF, the northern and central terrains experience a moderate fracture density, ranging from 0.96--2 . The high level of fracture density appears along zone. The southern tip of the study site exhibits a very high -2 Fig. 10B). Fig. 6B-D). The evidence is well-preserved on are displayed on a stereonet and a rose diagram to infer Fig. 11A). These data can be separated in two major groups based on principal compressional stress comes from the northwest- According to all lineaments, the combination of northwest compression and east-west tension suggests that the central segment of the MTF could be an extensional .

Geological field data and sediment analysis
The analysis of sediment bedload in eight channels reveals that overall sediment grain size varies from north to Fig. 12). The group of median sediment particles ranges from granules northern and central zones. The largest median bedload is approximately 6cm on channel 19. Toward the south, there is a gradual decrease in the median sediment particle size Table 3; Fig. 12). Our results reveal that the median sediment bedload and its variance D 10 and D 90 ) vary relative to variations in k sn values; higher k sn values correlate with coarser bedload, while lower k sn values correspond smaller sediment bedload size.

Implications of variations in geomorphic indices to rock uplift
The value of the channel steepness index is a proxy for Kirby et al., 2003Kirby et al., , 2007Kirby and Whipple, 2012;Snyder et al., 2003), Hurst et al., 2019). However, the normalized channel G e o l o g i c a A c t a , 2 1 . 4 , 1 -2 2 ( 2 0 2 3 )  D O I : 1 0 . 1 3 4 4 / G e o l o g i c a A c t a 2 0 2 3 . 2 1 . 4 Geomorphic controls on Mae Tha fault's eastern terrain 16 k sn Kirby and Whipple, 2012).
Our topographic analysis shows a three-to-fourfold decrease in normalized channel steepness indices toward the lower reaches as described in other settings by Hurst ).
i) channels adjust their morphology to the spatial variation processes on the landscape, and the fault movement and ii) the entire landscape is in the transient-state condition, fracture density. Our analysis averages the mean elevation their morphology and appear to retreat at the same rate

Channel steepness as a function of lithologic forcing
The eastern side of the MTF is a topographically rugged terrain in the mixed deciduous forest. The terrain et al., 1984 controlling spatial variation in channel adjustment.
The large extent of granite on the eastern terrain can The resistance of homogeneous granite is typically higher steepness: channel steepness in the upper reaches is twice Table 2; Fig. 9B). The differences in channel steepness imply that erosional processes on the granitic terrains are slower than the terrain underlaid by older clastic and meta clastic- Fig. 13A).
Although less-resistant clastic and metamorphic the northern zone, the presence of steeper lower channel reaches results from the coverage of large granitic pebbles and cobbles that are eroded and delivered from the steeper upper channel reaches. The cover effects from large sediment particles on the channel bed control the Channel ; 2006). These channel segments may be transferred to a transport-limited state where the high volume of sediment supply and larger size of sediment materials limits channel incision and channel steepness. Channel incision can re-occur when high shear stress/or stream power exceeds the threshold shear stress Snyder et al., 2003;Montgomery, 1999; Although the granitic lithologies underlie channels in the southern section, these present shorter and gentler sediment particle sizes on the channel bed are smaller compared to channels in the northern zone. The smaller    Figure 9A. The result of averaged grain size distribution illustrates that the median bedload sizes are large in channels 5 and 19. However, the median particle sizes become smaller toward the South. The figure represents variations in the relationship between channel steepness and their variance in the population (as described by the difference between D 10 and D 90 ). Grey: D 10 (mm), Blue: D 50 (mm), Black: D 90 (mm).

Mae Kuang Fault
Mae Tha Fault k sn Channel steepness as a function of tectonic forcing morphology to tectonic uplift and have not yet attained a steady-state condition. The channel steepness, channel width, and sediment cover patterns on the channel bed are spatially variable. Although we did not observe the width is variable throughout the length of the channels. Our analysis is restricted to the adjustment of channel are controlled by lithologic strength and the cover effects from larger sediment particles. Tectonically, the northern section is bounded by a west-dipping normal fault. The gradients are still high, the coupled effects of lithologic respect to the MTF causes a differential motion and uplift Rhodes et al., 2004).
west of granitic batholith consisting of interbedded white Uttamo, 2000). The uplift steepens and Mae Ruam rivers seems to explain the landmass's exhumation to a higher elevation.
The altitude of topography in the south is lower than lithologic substrates and cover effects may be subordinate to the role of tectonics and lineaments in controlling the shape of the terrain and the adjustment of channels. Due to the lower presence of local lineaments, the faultfault of the southern segment of the MTF. A reasonable explanation to lower elevation and gentler channel steepness in the southern zone is that these features are controlled by Fig. 13B). The interconnection between the major MTF, minor faults, and mass strength decreases, leading to smaller sediment grain effects from smaller clasts cannot protect the channel bed Molnar et al., 2007;Roy et al., 2016).
When comparing the spatial distribution of fracture density across the eastern terrain of the MTF, fracture density is inversely proportional to channel steepness and channel gradient; the moderate level of fracture density in the northern and central zones correlates to higher channel steepness and gradients, while the higher level of fracture density in the south associates with gentler channels and lower terrains. Therefore, the connection between tectonic This study shows the roles of tectonic and lithologic factors in controlling landscape topography along the MTF. At the same time, it serves as an example of how geomorphic analysis helps to understand landscape adjustment and evolution in tectonically active regions with similar conditions.

CONCLUSION
indices help to characterize the spatial adjustment of lithologic forcing along the eastern terrain of the Mae Tha are present. Our topographic analysis reveals a three-tofourfold decrease in channel steepness indices from north the channel are steeper than the lower reaches. region correlates to less-resistant geologic substrates, and central zones, steeper channels and high terrains are footwall side of the terrain and the strong cover effects of coarse bedload on the channel bed. Conversely, gentler channels and lower terrains in the south are controlled by and sediment particles can control spatial adjustment of Tha fault. Overall, our study provides an insight that the use of topographic adjustment analysis may contribute to explain the dynamics of active deformation of the landscape over space and time and to evaluate tectonic and lithologic forcing in tectonically active mountain ranges.