## 2 Materials and Methods
### Subsidence Causality Inputs  
The spatial and temporal context in an area of interest should be considered when defining the CSC causality inputs that could explain surface motion. Alexandria is one of the oldest cities in Africa and the Mediterranean Sea. It is the second largest city in Egypt and the main harbor city of the country. Located in a semi-arid area, Alexandria has only two climatic seasons: a moderate winter with very little rainfall from November to April, and a hot dry summer from May to October. The population of the city is more than five million with a population density of about 1800/km\({}^{2}\), based on Egyptian Statistical Office (CAPMS) data [8]. It was built by [PERSON] on the site of Rhakolis village in 331 BC [30]. The present city is located between 30\({}^{\circ}\)50\({}^{\prime}\) to 31\({}^{\circ}\)40\({}^{\prime}\) North and 29\({}^{\circ}\)40\({}^{\prime}\) to 32\({}^{\circ}\)35\({}^{\prime}\) East, Alexandria extends from Abu Qir Bay in the East to Sidi Krier in the West with a waterfront of about 70 km. This city has a commercial, industrial, business, and cultural importance in the country as almost 40% of Egyptian industry is located in or surrounding the city [8]. Alexandria is located in a tectonically stable area. Geologically, it is based on a cemented Pleistocene sandstone ridge, and covered by a thin layer of Nile Delta's Holocene sediments, except for the sandy tombolo that connects the paleo-island to the mainland. The carbonate sandstone ridge appears in some parts of the west in Alagami and east in Abu Qir. Geomorphologically, it consists of a low, near-horizontal topography within one meter above the mean sea level [31]. Most of the city lies on a long natural bay between the sea and Lake Mareotis at the western edge of the Nile Delta. Alexandria consists of three segments: beach resorts in the southwest, watersheds in the city center, and cape Abu Qir in the northeast [8; 30]. The southern parts of the city were formerly wetlands [6; 7]. This city experienced severe subsidence rates caused by short-term catastrophic events such as powerful earthquakes and tsunamis in the years 365 AD, 1303, and 1323 that resulted in a sudden failure of some parts of the city such as the eastern harbor [32]. In the last three decades, the city area has expanded rapidly. However, the major part of the urban expansion is unplanned with a lack of basic services and infrastructure for a large part of the population in those areas [8]. Figure 2 presents the study area of Alexandria city and its important features. The literature and field investigation controlled the subsidence causality factors selection in Alexandria. Our model-test-study started with a hypothesis of eight subsidence causality factors in Alexandria: rock type, former lakes and lagoon dewatering (FLLD) in dried and reclaimed lands, active faults, seismic activities, building load (BL), groundwater extraction, mining activities, and underground infrastructure. Field investigations revealed no large underground infrastructure in Alexandria that could influence surface subsidence due to its sensitive nature, nor mining activities which may influence surface motion of the city. Field investigations also revealed no groundwater extraction for irrigation in the study area due to the high salinity of the subsurface water (see also [17]). In addition, the seismic activities in the city have only a small influence on surface deformation as no  
Figure 2: Study area. Based on a background of a Sentinel-2 (S-2) infrared false color image acquired on 24 October 2018 (R: band 8, G: band 4, B: band 2), Figure 2 presents the study area with blue border, and main city areas names wrote in yellow color font. The S-2 infrared false color image shows vegetation in reddish colors, built-up areas in grayish colors, and salty swamps in greenish colors. earthquakes with a magnitude above five or six have been measured during the last century.