# Probabilistic Seismic Hazard Assessment for United Arab Emirates, Qatar and Bahrain
## 7 Results and Discussion
Such differences can be attributed to several factors: (a) a more updated earthquake catalog (until 2019) than those studies considered in the building regulations for the investigated countries has been used, (b) the different zoning models (three alternative source models weighted in a logic-tree design) implemented in our assessment, (c) the inclusion in this assessment of two different levels of seismicity, and corresponding potential seismic sources, in which the intermediate-depth seismicity was discriminated from the shallower one, and finally, (d) the selected ground-motion attenuation models used in this assessment are worldwide and region-specific models, differing from those considered in previous studies. Taking into consideration such differences, as well as the fact that some regulations for some emirates and cities only depend on the PGA value in the definition of the design spectra, we propose the application of a different approach for the formulation of the design spectra all over the studiedcountries. It can be defined using only two SA values (SA (0.2 s) and SA (1.0 s)). This approach was proposed by [PERSON] [106] based on the Newmark and Hall [107] procedure for the definition of a design spectrum, and following the same methodology as in the published works by [PERSON] et al. [114] for Northern Algeria and [PERSON] et al. [97] for Egypt. First, the so-called control period (T\({}_{\text{s}}\)) should be computed from the relationship between the SA (0.2 s) and SA (1.0 s) values obtained from the UHS, as the following:  
\[T_{S}=\frac{SA(1.0\text{s})}{SA(0.2\text{s})}.1\text{s} \tag{6}\]  
Next, the design spectrum is computed using the following equation:  
\[SA(T)=\left\{ \begin{array}{ccc}0.4\cdot SA(0.2\text{s})+3.0\cdot SA(0.2\text {s})\cdot\frac{T}{T_{s}}&&T\leq 0.2\cdot T_{s}\\ SA(0.2\text{s})&&0.2\cdot T_{s}<T<T_{s}\\ SA(1.0\text{s})\cdot\frac{1\text{s}}{T}&&T>T_{s}\end{array} \right. \tag{7}\]  
The proposed design spectra clearly show a better agreement with the computed UHS for the selected cities (see Figure 8). The reason is that the SA values at 0.2 and 1.0 s, clearly are representative to a great extent of the overall shape of the UHS. A final result from the current assessment is the seismic hazard deaggregation, for 475 years as return period, for four spectral periods, and depicted as bar charts for both magnitude and focal distance cells against the obtained hazard contribution (Figure 9). Each bar reflects a different earthquake scenario. The height of each bar is representative to the relative contribution of a specific earthquake scenario to the total obtained seismic hazard at the specific site. From the careful inspection of the displayed hazard deaggregation results in Figure 9 and the tabulated values for the modal and mean distance and magnitude values in Table 6, the selected emirates and cities could be categorized into two main groups. The first category consists of five emirates (Ras Al-Khaimah, Umm Al-Quwain, Ajman, Sharjah, and Dubai; see Figure 9), in which the shape of the deaggregation plots is characterized by a unimodal single-lobe distribution, in which the maximum (modal) peak is relatively close to the studied emirate, while the tail includes the more distant earthquakes. This means that the seismic hazard at the studied location is due to the closest potential seismic sources. In such case, both the mean and the modal value for the control earthquake nearly coincide. Range values of 94-149 km and 88-133 km (Table 6) were obtained for the mean distances for the control earthquake, for this group of emirates, for PGA and SA (0.2 s), respectively, taking into account the fact that the longer period of ground motion, the more contribution of distant earthquake is expected. For longer periods (SA (1.0 s) and SA (2.0 s)), the mean distance ranges for the control earthquake are reaching 163-221 km and 189-242 km, respectively.