Generally, local site effects (landslides, liquefaction, amplification and faulting systems) play an important role in the intensity of earthquakes. Thus, Earthquake-resistant design of new structures and evaluating the seismic vulnerability of existing buildings take into account their response to site ground motions. Geophysical studies of seismic activity in Palestine, deep seismic sounding, paleoseismic excavation, and instrumental earthquake studies of half a century demonstrate that damaging earthquakes occurred along the Dead Sea Transform fault. The topography, geomorphology and geology of the West Bank have been the main reasons behind several sizeable landslides that occurred around ten years ago in different parts of the West Bank. Also, it has been shown that Palestine suffered from several landslides during historical earthquakes.

Landslides are rock, earth, or debris flows on slopes due to gravity, and they can occur on any terrain given the right conditions of soil, moisture, and the angle of slope. Landslides can be triggered by rains, floods, earthquakes, and other natural causes as well as human-made causes, such as grading, terrain cutting and filling, excessive development, etc. Because the factors affecting landslides can be geophysical or human-made, they can occur in developed areas, undeveloped areas, or any area where the terrain was altered for roads, houses, utilities, buildings, and even for lawns in one's backyard.

To investigate landslides one should do field studies (including geophysical seismic study), laboratory studies and slope stability analysis. It is important that the field and laboratory investigations be supplemented by field measurements so that the behavior of a slope can be checked and corrective measures be taken in times. The first step in landslides analysis is the collection of available information geological, hydrological, topographical, and soil maps.

The subsurface geology determined by seismic studies is extremely important for the development of urban areas. The shallow upper part of the rock formation section is the most significant part for civil infrastructures. The seismic refraction technique is considered an accurate geophysical method to investigate the shallow geological structures of an area. During the past decades, the seismic parameters obtained by a refraction survey have been widely used in cases of site investigation as indicators of rock mass quality. These parameters are of great importance in land use management of various civil engineering purposes (Primary velocity Vp, shear wave velocity Vs and Soil profiles).

Several landslides occurred in Palestine during 2012 in which geophysical seismic explorations were used for slope stability analysis and landslides studies. Four major landslides are focused on, namely, Al Bathan – Nablus main road landslides, Nablus District, A’arrabeh landslides, Jenin District, Kufur Qalil landslides, Nablus District and Beit A’oor, Ramallah District.

In order to better understand the causes of landslides and slope instability in the above mentioned areas, it is important to describe soil strata, soil properties and the geotechnical conditions of these sites. These parameters and conditions at the study areas were found from the seismic geophysical investigation by using seismograph 24 channels, trial pits, lab tests and eye observations. Then, slope stability analysis using software GeoStudio2007 was carried out for several conditions along the critical sections in the studied areas to figure out the minimum factor of safety and comparing to the acceptable limits. In general, the factor of safety for slope required for any temporary structures is 1.3 and that for permanent structures it is 1.8.

During the presentation in the Workshop, these four major landslides which occurred in Palestine during 2012 will be focused on and results of slope stability analysis and landslides studies will be presented. Based on these analysis and studies the factor of safety found, it is clear that these sites suffer slope instability and hence, landslides may occur at any moment. Furthermore, soil properties may be changed at these sites due to weather conditions, such as, rainfall or snow fall or / and these sites will be affected by relative strong earthquakes. This will reduce the factor of safety and landslides may occur.

In general, several recommendations were suggested to overcome slope instability in sites were landslides occurred. Such recommendations are to reduce the weights at the top of slopes, increase and install weights at the bottom (toe) of the slope, flatten the slope, methods to drain the slope and the site around landslides, increase stability by planting trees on the slope.

It is found out as planning strategy; landuse policy should be done for Palestine, especially, for sites of high slopes and those of which they have previously landslides.