Lineaments Extraction and Analysis Using Landsat 8 (OLI/TIRS) in the Northeast of Morocco

Northeastern Morocco is made up of several units belonging to the Alpine belt and its foreland. Miocene to plio-quaternary volcanic rocks with variable mineralogy and geochemistry dominate the geology of this region. The presence of active faults in different directions explains the high tectonic instability and the high frequency of earthquakes. This study contributes to the effort of understanding the geothermal potential of the Northeast of Morocco. Heat source and permeability are both key factors in the geothermal process. Indeed, lineaments analysis constrains the structures and their directions and indicates severely faulted zones, which are the most promising areas for geothermal exploration. For this purpose, we used Landsat data combined with geological and structural maps available in this region. Different image processing techniques were applied including band ratio (6/2) and directional filters. To validate the results, we conducted a comparative study between linear structures, available geological data, and previous studies. Results of the automatic extraction method of lineaments from Landsat 8 OLI/TIRS indicate three main lineament systems: 1) a NE-SW system ranging from N40 to N70; 2) an N-S system ranging from N10 to N45; 3) an EW to WNW-ESE systems ranging from N80 to N120. Most of lineaments extracted are localized in Kebdana, Amejjaou, Nador and Melilla regions. Compared to previous studies, the NE-SW system is consistent with an extensive period (Tortonian to Pliocene); the NW-SE system is consistent with the last compressive episode (Pliocene); the N-S system is consistent with the first compressive period (Late/End Tortonian). How to cite this paper: Redouane, M., Mhamdi, H.S., Haissen, F., Raji, M. and Sadki, O. (2022) Lineaments Extraction and Analysis Using Landsat 8 (OLI/TIRS) in the Northeast of Morocco. Open Journal of Geology, 12, 333-357. https://doi.org/10.4236/ojg.2022.125018 Received: April 11, 2022 Accepted: May 24, 2022 Published: May 27, 2022 Copyright © 2022 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/


Introduction
In the last few years, remote sensing has been a very promising tool for researchers in different disciplines, including mining exploration [1] [2] [3] [4] and geological mapping ( [5] [6] [7] and references therein). Many approaches were developed with the aim of identifying morphological and structural lineaments [8]- [28]. Such methods use geomorphologic signatures deduced from high spatial resolution images, such as Landsat ETM+, OLI/TIRS, and Sentinel.
Three main lineament interpretation methods are usually adopted as follows: manual lineament interpretation, automatic lineament extraction and semi-automatic extraction. The visual interpretation consists of textural patterns related to geomorphological features and tonal contrast [29] [30] while the automatic extraction uses computer algorithms. Image enhancement and filtering options are applied to processed images with different image processing techniques, for instance, Principal Component Analysis (PCA) and band ratio (e.g. [31] [32] [33] [34]). The processing for lineament extraction purposes is usually performed on grey-colour spanning images instead of colored images because it gives better results as the contrast is better exposed in black and white versions [35]. The filters are chosen afterward and applied using software (e.g. Geomatica), which can be either directional [31] [32] non-directional [30] [36] or both [37] [38]. A recent study [39] has questioned both filtering techniques while extracting lineaments and got better results with directional filtering compared to non-directional filtering. However, the application of direction filters may produce some artefacts [40], which can be confusing, and should be corrected and revised. To minimize the errors resulting from visual interpretation, several authors [41] [42] suggest doing the same process several times with a week break at least and then comparing it with interpretations of the same operation of another observer.
The northeast of Morocco consists of two orogenic belts, the Rif chain in the north and an intracontinental belt called the Atlas, developed within the alpine tectonic foreland [43], to the south. The study area borders the junction between these domains, where three structural units directed ENE-WSW were previously identified [44]: 1) the eastern-rifian foreland; 2) Guercif and Taourirt-Oujda ba-during the Late Triassic period, which mainly consisted of red mudstones, carbonates and tholeiitic basalts [47]. A carbonate platform was developed in the Early Liassic, and was cut later by a series of extensional faults forming a pattern of grabens and horsts oriented ENE-WSW and E-W. Then, a major NNW-SSE extension occurred between the Jurassic and the Early Cretaceous [48]. This extension was followed by a long compressive event, which started in the Eocene and created the NW-SE and NNE-SSW strike-slip faults and the E-W folds, and persisted to the Miocene [48] when volcanism took place.
The study area is known for a Plio-quaternary volcanic activity and a large number of geothermal manifestations ( Figure 1). The lack of subsurface imaging data in geothermal areas encourages geologists to acquire more surface information and infer the subsurface geologic conditions (e.g. mineral alteration, permeability…). Lineaments, as extractable geological features, refer to rock fractures, joints and faults. The latter plays a key role in creating the porosity and permeability, which allows the capture and storage of thermal fluids in a geothermal system. Thus, characterizing these features shall contribute significantly to the understanding of the fluids' behaviour in a geothermal reservoir. In this paper, we applied the automatic extraction method using a Landsat8 (OLI/TIRS) image, covering northeastern Morocco, then, we applied the visual inspection to add and remove lineaments in order to construct a map of tectonic lineaments. The results are remarkably important as they demonstrate that the automatic extraction method can indicate the presence of small fractures, hardly detected in the field, their global directions and density and hence can be a good prospect for permeability.

Geological Settings
Rif-Tell belt is an Alpine system, resulting from the progressive closure of the Maghrebian Tethys and slab rollback of its lithosphere since the late Eocene [49]. The Rif belt (Figure 1  beneath NE Morocco is anomalously thinned extending far to the South (Agadir) [51], delineating what is called "The Moroccan hot line" defined by [52] ( Figure 1(a)). The Tertiary alkaline volcanism observed within the area in Gourougou (Nador), Guilliz (Guercif) and Oujda volcanic provinces is related to this hot line. This volcanism is also reported in the Middle Atlas (the most important province) and in the Anti-Atlas (Siroua and Saghro) [53] [54], where high magnetic anomalies were found [55]. Many tectonic models were proposed to discuss their origin (e.g. [50] [52] [53] [54] [56]), however, the relationship between different volcanic episodes is still a matter of debate. On one hand, the presence of NE-SW major strike-slip faults and structures crossing from Agadir to the High and Middle Atlas, associated with faults in the eastern Rif (Nekor) led many authors [53] [59] [60] to suggest a fault system referred as "en echelon". Most of those faults cross the Alboran Sea and link up with the easternmost part of the Betics [61].
On the other hand, the Eastern Morocco volcanism is settled on Upper Miocene sedimentary basins [53]. Many authors [62] suggested subduction as the main cause of this magmatic activity; however, this hypothesis could not be corroborated because of the lack of any chronological or geochemical polarity. Thus, the model of a transverse strike-slip system, occurring between Iberia and Africa, linking both crusts and affecting the entire lithosphere, was highly recommended by [63] and supported by geochemical data (e.g. [50] [54] [64]). Results showed that Neogene magmatic activity is predominantly related to an extensional regime created by the upwelling of a mantle source, enriched during the previous subduction, while the Plio-quaternary volcanism is related to a compressional system, with an enriched lithospheric mantle source and a possible asthenospheric depleted mantle.
The compressional stress regime in Northeast of Morocco displayed since Tortonian volcanic activity three sedimentary and eruptive bodies ( Figure 1), these elements recorded the chronology of tectonic events [65] [66]:  The first is a N40 compressive stress trend is responsible for the development of Tortonian basins. Kebdana and Temsamane basins are developed along strike-slip faults oriented N70 -N90, while N-S and N40 -50 trends are responsible for forming Boudinar and Nekor basins, respectively. Calc-alkaline volcanism of Ras Tarf and Trois Fourches is associated with the basins of Boudinar and Nekor [67].  The second is a compressive stress-oriented N-S and occurs in late Tortonian and during the Messinian. A reverse movement is registered along N90 faults in addition to strike-slip movement on faults striking N70, N40 -50 and N-S. Those movements were the expression of a variation in paleostress direction and led to the development of Guercif, Boudinar and Kert basins [61] [67]. The E-W extension in the Northeast of Morocco is responsible for normal faults, oriented N-S, frequently exposed all over the post-nappes basins. This event was synchronous with shoshonitic volcanic eruptions in Nador and Guercif regions (Gourougou and Guilliz) [53].
 The third consists of a counterclockwise rotation of the stress field with a max. Compressive stress-oriented N140 -160 [66], N90 and N120 -140 structures are mainly dextral strike-slip faults while the N-S structures are sinistral. Faults oriented N40 -70 are reactivated with a sinistral behaviour [67]. Previous studies (e.g. [61] [65] [66] [68]- [73]) recorded that this compressive stress (N140 -160) has been well identified all over the Northeast of Morocco (from Rif basins to middle and high Atlas). The alkaline activity took place during the same period in the eastern Rif and its foreland [53] [74]. The split of several blocks showing an alternation of horst and troughs has characterized the Neotectonic evolution of Northeast of Morocco. Compressive and extensive stress regimes at this time were associated simultaneously [67]. Different structures presented in Northeast of Morocco (Figure 2), including the numerous volcanic intrusions (veins, eruptive centres, etc.) feeding the lava flows, are formed following three major directions: NE-SW, NW-SE and N-S. Consequently, volcanic emissions seem to be parallel to faults trending N70 -90, N40 -50 and N-S, dominating the area's structure; N120 -140 faults are locally associated [67].

Data
In this paper, we work on Northeast of Morocco. The image used is landsat8 OLI/TIRS (Path 201 and Row 36, taken on 9th January 2019) and the data is available free at the United States Geological Survey website (https://earthexplorer.usgs.gov). It is provided with the Universal Transverse Mercator (UTM) projection and a WGS 84 World Geodetic System. This image contains eleven bands with different wavelengths and resolutions (Table 1)

Methods
The main step of lineament extraction is described in the following chart ( Figure 3). It starts with pre-processing, consisting of radiometric and atmospheric corrections, then the processing, to enhance the visibility of lineaments in the images. The main purpose is to identify lineaments with possible structural origins. After several attempts using different image processing techniques, classifications and colour composite images, we concluded that linear structures are more visible in the 6/2 band ratio images, the choice is also supported by other studies (e.g. [78]). Hence, the ratio of 6/2 image was sharpened and directional filters were applied (Figure 3).

Enhancement of Lineaments by Filtering
Directional filters improve lineaments' perception by producing an optical shadow effect adjusted on the image as if it was enlightened by grazing light [79]. Besides, those filters enhance the detection of lineaments, which are not advantaged by the illumination source [80]. We used Sobel operators, widely utilized for lineament extraction and edge detection [81], to enhance the lineaments automatically extracted from directional filters. Sobel filters consist of a selective variety of directional filters using a pair of convolution matrix of 3 * 3, one of them is the other mask rotated by 90˚ (Table 2), and is determined based on the distance from the central pixel. In this study, the image used for the filtering is Ratio 6/2. From these directional filter images (Figure 4), the lineaments are automatically extracted, however, the result is not definitive, the work is still incomplete and a visual method must be used before reaching the next step of confirmation and validation.

Tracing and Validation of Structural Lineaments
After enhancing the edges by directional filtering, we opted for visual inspection [82] [83]. This method allows choosing the significant lineaments of structural origin. Validation of fractures consists mainly of eliminating linear structures related to different parameters (e.g. ridgeline, shade, etc.), so we first compare our map of lineaments with geological and pre-existing structural maps. Open Journal of Geology

Results
Results reveal the existence of more than 4600 lineaments ( Figure 5, Figures  6(a)-(c), Figure 7(a) and Figure 7(b)). The length of structures varies and spans from few meters to few kilometers, the longest representable lineament is about 4 kilometers (Figure 6(a)). Rose diagram (Figure 7     revealing zones with high structural density. Two areas have the highest densities: the first is Kebdana, close to Kariat Arekmane and Ras el Ma, reported in the geological map as formed by Jurassic limestone; the second is Amejjaou, in the west of Seghanghan and Nador, described in the geological map as a part of the Temsamane unit, consisting mainly of Shists. Areas of Nador, Melilla and the coastal limit with Algeria show a high density as well. Compared to materials used for validation, the number of highlighted structures within the area is more important in this study than the number of linear structures in geologic and structural maps, made based on fieldwork. Mapped lineaments generally correspond to fractures and faults, mainly related to vol-canic outcrops, Miocene basins and Jurassic terrains. The fracture is usually a result of breaking a rock in response to stress, if one of the two sides of the fracture moved, it is no longer a simple fracture, but a fault that has a couple of well-known criteria.

Discussion
The northeast of Morocco represents a very dynamic area. It is related to excessive tectonic regimes since the Late-Miocene with many phases of deformations [84] [85]. The current deformation under the transtensive regime (NNW-SSE to N-S extensive system and NNE-SSW strike-slip faults), in the South of Alboran Ridge and Nekor Basin, is limited by Al-Idrissi fault (Figure 1(b)) [86]. Geodetic studies and kinematic models based on magnetic anomalies of the ocean floor show a current convergent movement of plates in Alboran sea, oriented NW-SE with a speed of 4.3 ± 0.5 mm/yr [87]- [93] and a displacement in the Rif belt towards the southwest with a speed of 5.4 ± 1.5 mm/yr. Whereas the regional seismological studies show: A NE-SW extension in the Southern Betics, together with strike-slips [ [102]. A polyphase tectonic history, resulting from several successive compressive and distensive phases from Eocene to the present, is well documented in northeastern Rif [103]. It begins with an oligocene tightening phase-oriented N-S, then it continues with a distensive oligo-miocene phase with the same direction N-S linked to the opening of the Alboran sea, and it ends with an overlap of Carbonate thrusts of Alboran Domain ''Bokkoya massif'' on the Flysch domain in the SSE (Figure 1(b)). Finally, the late compressive NNE-SSW Tortonian phase made the last remarkable structures [103] [104] [105] [106]. Since the late Miocene, surface crustal deformation caused kilometric-sized folds and brittle deformation, associated with the development of large strike-slip faults (i.e., the Nekor fault between Al Hoceima and Nador (Figure 1)). Faults' pattern in central and eastern Rif is sorted into three groups, two of which are almost orthogonal: one in the NNE-SSW direction, and one in the NS direction, perpendicular to the coastline, and a last one in NW-SE (Figure 9) [105] [107] [108] [109] [110].  Then, a compressive period, during the upper Pliocene and the early Quaternary, oriented NW-SE and well visible in the Northern border of Gharb and Guercif basins. Finally, an extensive period in Quaternary, oriented NE-SW and marked by the most recent features, where the subsidence is well-conserved [107].
Although the E-W trend (poorly cited in literature), identified in this study, is consistent with Belt axis and directions of magnetic anomalies beneath the surface in the northeast part of the Rif [111].
On one hand, previous studies on tectonic movements, lineaments and geospatial information in the northeast of Morocco are very limited. The most recent work dealing with the topic in the area [112] used Landsat image analysis and compared the results with data obtained from radar ERS1-SAR interpretation [113], Spot image analysis [114] and structural field analysis. Four systems of faults were depicted [112]: 1) NE-SW faults with a pattern of en echelon structures (e.g. in the El Aïoun area), recorded during their fieldwork; 2) NW-SE faults; 3) ENE-WSW and E-W faults; 4) faults trending N-S, mainly in Oujda area (Bou Yahi). Although the frame of the current study area and the studied area of the cited work is not exactly the same, it can be considered and used for comparison, as they both share the same geodynamic and geographic settings. Regarding the orientation of present structures, all directions are conformably expressed within the northeast of Morocco; however, the frequency and the dominance are relatively different. NW-SE trending faults, for instance, are the second most dominant faults in the work of [112], while it is the least dominant in this study. This difference might be explained by the dominance of Rif belt structures over Foreland structures within the area (for the current work).
On the other hand, our results were confronted with results of a similar study on NE of Iberia. The latter shows that the bulk of major post-Alpine extensional faults, mainly Neogene, are oriented NW-SE. Secondary structural lineaments, however, show an NNW-SSE trend, running slightly in an oblique way to the main faults [115]. Eruptive fissures and subordinated structural lineaments in northeastern Spain show a pattern, compatible, structurally, with a light dextral transtensional component in two major Neogene faults (Amer and Llora faults), oriented NW-SE [116] [117].
[118] [119] were the first to suggest the idea of magmas taking the way upward in the uppermost crust and subordinated fissures, controlling subsequent eruptions, making this pattern an enhancer to the development of fractures and transport of magma through them [115]. This behaviour apparently is not an exception, though it was described in some other volcanic zones [120]. Within the same area in the NE of Spain, eruptive centres are aligned mainly NW-SE to NNW-SSE, having a sub-parallel trend with lineaments. This orientation might be the reflection of magma-feeding fractures' geometry [115] [121] [122]. A secondary group of volcanic features is elongated NE-SW and ENE-WSW [115].
In the northeast of Morocco, recent volcanic formations towards the south and the southeast of the study area show normal faults trending from N160˚E to N10˚E [123]. Volcanic flows are aligned along the fissures striking N-S (Oujda region) or exactly at the intersection between N-S normal faults and ENE-WSW strike-slip faults (with a reverse component). The general trend of volcanic outcrops, on a larger scale, is NE-SW to E-W, conformably with the most predominant lineament trend in the northeastern Rif (mainly NE-SW and E-W). This conclusion supports the idea of having a pattern controlling the magma ascension with a preferable direction NE-SW.

Conclusions
Combining eye detection with an automatic extraction method using satellite images gave us better results so far. Firstly, it reduces the time of the processing by defining the most likely zones where lineaments could be important in size and distribution. Moreover, it detects the small lineaments, hardly detected onsite. Secondly, structural lineaments are easily selected and rectified once the analysis of detected linear structures is done and suppression of insignificant lineaments (corresponding to roads, rivers, agriculture squares, etc.) is completed. Using only the automatic extraction therefore will not be of high precision and effectiveness.
To summarize, lineament's directions detected from coupling the two methods yield more accurate results. Trends represented in the northeast of Morocco, rating by their abundance within the study area, are NE-SW, E-W, NNE-SSW, N-S and NW-SE. The NE-SW and the E-W trends are the most overriding based on this study, which explains why volcanic outcrops are aligned in the same direction. Northeast of Morocco must have a cracking pattern, similar to the one described in the NE of Spain, leading to a close behavior and hence reflecting the geometry of magma-feeding fractures in north of Morocco. These results have major implications in the undergoing geothermal study within the area, especially in understanding the subsurface flow of thermal fluids in geothermal reservoirs and avoiding serious risks during the geothermal drilling projects.