How an earthquake in Zhetisu was felt in Almaty: Seismologist explains

Tengrinews.kz – Kazakh seismologist Mukhtar Khaidarov provided insights into the recent earthquakes in the Zhetisu region and why they were felt as far as Almaty.
Mukhtar Khaidarov, a seismologist, candidate of physical and mathematical sciences, and advisor for seismic safety and mobilization preparedness at the Almaty city administration, highlighted an increase in seismic activity in eastern Kazakhstan, particularly near the border with China.

“The location of the earthquake was in the Altyn-Emel fault zone, specifically its eastern edge. This fault is not in the highest category of seismic activity but in the medium one, where moderate earthquakes usually occur without alarming the public. However, at the other end of this fault lies the Kapshagay Reservoir. The proximity of faults and bodies of water is always concerning for seismologists as it triggers seismic activity. We are currently observing this around Kapshagay and Konaev, with minor seismic activity that is not felt by residents, involving tremors of less than two magnitudes. This activity, however, is increasing and is related to the reservoir. Globally, the proximity of reservoirs to seismic zones is undesirable,” Khaidarov explained.

Why Almaty felt the tremors
According to Khaidarov, the strongest tremors, measured at 4.0 on the intensity scale, were felt in the Chundzha area due to specific local features.

“The intensity depends on the water saturation of the terrain. The Almaty and Zhetisu regions are currently highly saturated with water. Additionally, uneven terrain can add about one point to the intensity of tremors. From what I know, Chundzha is a mountainous area, so the tremors could be felt at 4.0 there, while in Tekeli, Zharkent, and other locations, the intensity was around 2-3. In Almaty, tremors were felt at 2.0, even though the earthquake occurred 250 kilometers away. This is due to the depth of the epicenter. Typically, earthquakes in our region occur at depths of 10-15 kilometers, which are known as crustal earthquakes. The Earth’s crust in our area is about 35-40 kilometers thick. According to the US Geological Survey (USGS), the depth of this earthquake was around 45 kilometers. The European-Mediterranean Seismological Centre (EMSC) recorded a depth of 30 kilometers. Such deep earthquakes spread over larger distances but with reduced intensity at the surface, making them less dangerous. Seismologists welcome such events as they do not cause casualties,” Khaidarov said.

Influence of seismic activity from other regions
Khaidarov noted that increased seismic activity in this part of Kazakhstan might have been indirectly influenced by deep seismic events in the Pamir-Hindu Kush zone, where tremors occur at depths of 70-150 kilometers.

“While I lack definitive data to confirm this, the influence at the asthenosphere level (a layer in the Earth’s upper mantle) could impact the seismicity of our region,” Khaidarov added.

According to data from emsc-csem.org, Khaidarov elaborated:

“Three earthquakes to the south had focal depths of 300, 150, and 150 kilometers, suggesting activity in the Hindu Kush deep zone. The continuation of these epicenters' line intersects our Tian Shan mountains and seems to reach the Dzungarian mountains, where the recent 4.5 magnitude earthquake occurred. Its depth, whether 45 or 30 kilometers as per USGS or EMSC data, is still significant. Due to their depth, these earthquakes do not pose a serious threat to the population,” he explained.

The earthquake was recorded at 11:42 PM Astana time, 257 kilometers northeast of Almaty. The strongest tremors were reported in Chundzha, Zharkent, and Tekeli.