Sichuan Quake Swarm Continues; No Casualties in Gaoxian

A cluster of shallow earthquakes struck Gaoxian county in Yibin, Sichuan province on the morning of September 26, prompting China’s national earthquake agency to activate an emergency response, but authorities reported no casualties or injuries. The China Earthquake Networks Center (CENC) formally recorded three quakes that morning: a magnitude 4.5 at 05:01, a magnitude 3.4 at 05:08, and a magnitude 4.4 at 07:57 — the last of which the agency confirmed at a depth of just 5 kilometers.

The tremors are the latest in an officially recognized earthquake swarm that has shaken the region for nearly three months, since a magnitude 5.5 quake struck on June 29.

No Casualties, but Strong Shaking

According to Xinhua, officials in the areas nearest the epicenter — Gaoxian and neighboring Gongxian — told reporters that because the source depth was relatively shallow, the shaking was noticeable and lasted a relatively long time.

“No casualty reports had been received so far, and a new round of disaster and hazard inspections is under way,” the officials said.

The shallow depth also explains why the quakes were widely felt despite modest magnitudes. Per The Beijing News, citing the Sichuan Earthquake Administration, two factors amplify shaking in this region: earthquakes originate near the surface, allowing short-period surface waves to reach the ground with little energy loss; and the thick, soft sedimentary layers of the Sichuan Basin act like an “amplifier,” further magnifying ground motion.

National Emergency Response Activated

After the first magnitude 4.5 quake, the China Earthquake Administration (CEA) activated a Level IV emergency response, coordinating the CENC and the Sichuan Earthquake Administration and ordering joint consultation, strengthened monitoring and analysis, and prompt reporting. The Sichuan Earthquake Administration dispatched a field team to the affected area to assist local government emergency response, Beijing Daily and CCTV News reported.

The epicenter is located about 16 kilometers from Gaoxian county seat, 27 kilometers from Yibin city, and roughly 237 kilometers from the provincial capital Chengdu, according to CENC data. The area lies within a Seismic Intensity VI fortification zone.

A Months-Long Swarm, Not an Isolated Event

The September 26 tremors are not an isolated occurrence. The current sequence began with a magnitude 5.5 quake on June 29, which injured 13 people — all with minor injuries — and prompted the evacuation and resettlement of hundreds, according to The Beijing News. The same report noted that the city activated a Level III earthquake emergency response, and shaking was felt as far away as Chengdu, Leshan, and Chongqing.

Since then, the sequence has produced a steady stream of felt quakes. As of August 8, the Gaoxian M5.5 sequence had generated eight earthquakes of magnitude 4 or above, including two M5.0 quakes on July 8, an M4.9 on July 9, an M4.8 on August 3, and an M4.9 on August 7, according to the Sichuan Earthquake Administration.

The agency has classified the sequence as a typical “swarm-type” earthquake series — one characterized by fluctuating magnitudes and repeated quakes over a short period — and has said that aftershock activity will continue for some time. In this region, it noted, aftershocks can persist for years; magnitude 3-level quakes are still being recorded in the aftershock zone of the 2019 Changning M6.0 earthquake.

Experts point to the region’s geology. Gaoxian sits at the junction of Sichuan, Yunnan, and Guizhou provinces, on the southern edge of the Sichuan Basin where it transitions toward the Yunnan-Guizhou Plateau — a setting that produces broken rock strata and complex tectonic stress. Sichuan Earthquake Administration senior engineer Long Feng told Sichuan Online that the sequence’s spatial distribution lies closer to the Huaying Mountain fault zone, and that southern Sichuan hosts numerous fold structures and pre-existing faults that can rupture when the stress field is disturbed.

The region has a long seismic history: 26 earthquakes of magnitude 5 or above have been recorded since 1610, including the 2019 Changning M6.0 and 2021 Luxian M6.0 events. No magnitude 7 or higher quake has been recorded since 1900.

The Shale Gas Question

Yibin is a major hub of shale gas development in southern Sichuan, and since the swarm began, some residents have publicly questioned whether hydraulic fracturing is triggering the earthquakes.

Official experts have repeatedly ruled out a shale gas link. In a widely shared analysis, the science author Xu Xiake outlined the reasoning: the quakes originate 5 to 8 kilometers underground, while shale gas fracturing occurs at only 2 to 4 kilometers depth, with thick rock layers in between; hydraulic fracturing typically induces only micro-seismic events below magnitude 3 and cannot trigger magnitude 5-plus quakes; and the region’s 26 magnitude 5-plus quakes since 1610 point to a naturally active seismic zone.

Still, attribution is not straightforward. Xu noted that because detailed engineering data — injection volumes, pressures, and well locations — are not well disclosed, conclusions about any single event must be drawn statistically rather than definitively.

What to Watch

With the CEA’s monitoring and tracking efforts continuing and the sequence showing no sign of fully subsiding, attention now turns to whether the swarm will produce stronger tremors and how authorities will address persistent public concern about the region’s controversial energy industry.

For now, officials stress that the September 26 quakes caused no reported harm. The coming weeks will reveal whether the months-long sequence gradually decays — as the Sichuan Earthquake Administration expects — or delivers another significant jolt to a region already on edge.