## 4 Discussion  
The Malaysian coastline varies from scenic bays flanked by rocky headlands to shallow mud flats buffered by mangrove forests [11; 29]. However, there are some differences between the East Coast of Peninsula Malaysia and the West Coast. The coastline setting for the East Coast is a hook-shaped sandy bays because of the high sediment yield from river discharge confront the harsh wave environment, whilst mild wave climate of the Straits of Malacca makes wide mud shores in the West Coast and coastal forest-rich biodiversity [11]. The present study area covers part of the West Coast. However, the two study sites have different natural sediment characteristics (Figure 11). Site 1, Batu Ferringhi, is located on the north coast of Penang Island of the western coast of Peninsula Malaysia on the Malacca Strait. The tidal range in this site is microtidal (less than 2 m) [39]. The site is surrounded by Triassic biotite granite, which weathering product is manifested in the shore sediment, mixing with sand, silts, and even shells with some patches of gravel and granite boulders [9; 11; 39]. Meanwhile Site 2, Persiaran Bayan Indah, is anthropogenic land. It is located on the southeast coast of Penang Island on the western coast of Peninsular Malaysia on the Malacca Strait, facing east towards Jerejak Island. The area is protected from waves. The natural sediment before reclamation was composed of wide mud from the river discharge [9]. The existence of Jerejak Island makes the deposition of mud wider in this area. Figure 11: Comparison between (**a**) lithology map (modified from [40]) and (**b**) geomorphology map of the overall Penang Island. Both sites are beach landforms. Symbol 1 and 2 represent the survey site 1 and survey site 2. Batu Ferringhi (Site 1) is considered an undisturbed beach landform. The sediment deposition is natural, compact, and continuous. The GPR survey on this natural coastal landform shows flat compaction along the profiles; strong and continuous reflectors; a saturated zone as indicated by the reflection seems to be compact with two different upper and lower layers (cyan boxes as seen in Figure 4b); radar signals penetration is limited (less than 2 m); at a depth of more than 2 m dry conditions were indicated and the signals started to blur. The interruption of a man-made structure naturally forms a cross-sedimentary bedding structure (Figure 4). Indeed, the GPR method can be used further to analyze processes such as sediment depositional processes as claimed by [41]. The GPR responses in the coastal reclaimed land (Site 2) are very different. Here, the anthropogenic coastal landform shows undulating reflectors (green lines as seen in Figure 5). The surface layer with a flat surface and an undulating bottom at the scale of meters to hundreds of meters is widespread and typical of anthropogenically-affected fluvial depositional environments [42]. Discontinuous reflectors are visible in certain parts due to utility pole penetration or human activities; radar signals penetrated deeper (approximately 5 m), so it reveals more reflectors; at a depth of 1.5 m reflections corresponding to top filling sediments with some tiny reflections that penetrate through as the unsaturated reclamation area as seen. As seen in Figure 6a-d (Site 2), the three clear reflectors are the main characteristic of anthropogenic landform. Anthropogenic coastal landforms undergo a two to three times filling process followed by foundation treatment [43]. The first filling material is called the subgrade. When the subgrade material compacts after a certain period, the subsequent filling called sub-base is dumped on the first filling material. The process is repeated for the third filling material called a base layer. The three clear reflection events indicate this sub-grade layer, sub-base layer, and base layer of the reclaimed land [44].