Integrating Outcomes from Probabilistic and Deterministic Seismic Hazard Analysis in the Tien Shan

Abstract

In this study, we have evaluated the probabilistic and deterministic seismic hazard for the city of Almaty, the largest city in Kazakhstan, which has a population of nearly 2 million people.Almaty is located in the Tien Shan mountain belt, a low strain rate environment within the interior of the Eurasian plate that is characterized by large, infrequent earthquakes. A robust assessment of seismic hazard for Almaty is challenging because current knowledge about the occurrence of large earthquakes is limited due to the short duration of the earthquake catalogue and only partial information about the geometry, rupture behaviour, slip rate, and the maximum expected earthquake magnitude of the faults in the area. The impact that this incomplete knowledge has on assessing seismic hazard in this area can be overcome by using both probabilistic and deterministic approaches and integrating the results.First, we simulate ground shaking scenarios for three destructive historical earthquakes that occurred in the Northern Tien Shan in 1887, 1889 and 1911, using ground motion prediction 2 equations (GMPEs) and realistic fault rupture models based on recent geomorphological studies. We show that the large variability in the GMPEs results in large uncertainty in the ground motion simulations. Then, we estimate the seismic hazard probabilistically using a Monte Carlo-based PSHA and the earthquake catalogue compiled from the databases of the International Seismological Centre and the British Geological Survey. The results show that earthquakes of Mw 7.0 to 7.5 at Joyner-Boore distances of less than 10 km from the city pose a significant hazard to Almaty due to their proximity. These potential future earthquakes are similar to the 1887 Verny earthquake in terms of their magnitude and distance from Almaty.Unfortunately, this is the least well understood of the destructive historical earthquakes that have occurred in the Northern Tien Shan.

Significant Seismic Risk Potential From Buried Faults Beneath Almaty City, Kazakhstan, Revealed From High‐Resolution Satellite DEMs

“…The peak ground accelerations we calculate for Almaty (Figure ) are very similar to those of Mosca et al. (2019), in which Almaty likely experienced 0.5–0.6 PGA for the Verny earthquake and 0.3–0.4 PGA for the Chon Kemin earthquake. For their Chilik scenario, Almaty experienced 0.1–0.2 PGA, which is higher than the 0–0.1 PGA in our scenario.…”

“…The peak ground accelerations we calculate for Almaty (suppleentary figure S4) are very similar to those of Mosca et al (2019), in which Almaty likely experienced ∼0.5-0.6g PGA for the Verny earthquake and ∼0.3-0.4g PGA for the Chon Kemin earthquake.…”

“…Mosca et al. (2019) selected GMPEs that implement a mixture of the (Chiou & Youngs, 2014) and rupture‐site metrics (Akkar et al., 2014; Boore et al., 2014). is the Joyner‐Boore distance, which is the distance between the site and the closest point of surface projection of the rupture surface, that is, all sites located vertically above the rupture surface have equal to 0 and the largest values of shaking; the depth of the fault below the surface is not taken into account.…”

“…Here we modify their input ruptures for these earthquakes, suggest further earthquakes that may present hazard and additionally calculate the losses and damages in Almaty due to these earthquakes. Mosca et al (2019) selected…”

“…The historical earthquake scenarios provide a baseline to understand the impact if these past earthquakes were to happen today. We extend the work of Mosca et al (2019) by calculating not only seismic hazard in terms of estimated levels of ground shaking, but additionally the potential risk to Almaty in terms of damaged buildings and loss of life. We present the damage to residential buildings and the human and economic losses due to these earthquake scenarios, and identify which scenario is most damaging.…”