## 2 Materials and Methods
### Collected Data  
The local governorate of Alexandria started to record building collapse data in 2001, as a result of the increasing number of collapsed buildings over time. We collected all collapsed buildings recorded between the January 2001 and May 2019 from local district governmental offices. A total of 255 buildings collapsed during this period, as shown in Figure 2. Recorded data have only a descriptive location based on the street names and building numbers without available x and y coordinates provided in the governmental records. Hence, we used a hand-held Garmin GPSMAP 78 with three meters precision to collect the location of each collapsed building based on their recorded address. We have to address some difficulties that may affect the precision of our GPS points of collapsed buildings, such as narrow streets with high buildings, inaccessible areas for safety, and security reasons that forced us to sometimes read locations a short distance from the incident place.  
A total of 115 buildings completely collapsed, while 140 buildings partially collapsed, varying from a whole side collapse to a wall or balcony collapse. The dramatic increase in collapse incidents conditions, starting from 2014, was interpreted from the recorded data to weather conditions, old buildings' rooftop additions, and several fire and explosion incidents. We excluded ten collapsed buildings from our study processing, because they collapsed due to fire, explosion, and car accidents. Then, incidents were classified based on the collapse degree. Whole building collapse was classified as the highest collapse level of 4. Buildings that have the main vertical collapsed part of it as a whole side of a building were given the second severe level of 3. Level 2 was given for a building with several collapsed parts or inner collapse, such as the stairs of the building. The lowest level of building collapse of 1 was for small collapse parts of the building that are within a room ceiling, balcony, or a wall. Buildings with collapse level 1 were excluded from our analysis, and the remaining collapsed buildings for the analysis were 68, in the period between May 2015 and December 2018.  
Sentinel-1 is a C-band two-satellite constellation radar sensor; Sentinel-1A and 1B were launched in 2014 and 2016, respectively. Sentinel-1 data are provided as open-access data with global coverage. It has a geometric resolution of approximately 5 m in range and 20 m in azimuth [21]. In comparison  
Figure 2: Annual distribution of collapsed buildings in Alexandria between January 2001 and May 2019.  
to high-resolution X-band sensor data, the longer wavelength and the moderate geometric resolution result in fewer PS points on each building. However, the density of PS points we found is enough for our study to reach a conclusion on the spatiotemporal patterns related to building collapse incidents in the city. We used the same dataset of Sentinel-1 (S1) Single Look Complex (SLC) of our previous study [18] for the PS-InSAR processing in Alexandria. This dataset consists of 124 ascending images and 129 descending images with an average temporal baseline of 12 days, acquired in the period between January 2015 and May 2019. Additionally, secondary data of a soil map, areas of former lakes and lagoon (FLL), and the historical evolution of the city extent were collected for correlation test purposes.