The 2021 Luxian earthquake was a damaging

seismic event An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fro ...

occurring in the early hours of September 16 at 04:33 China Standard Time. The

surface wave magnitude The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This ma ...

() 6.0 or moment magnitude () 5.4 earthquake struck at a shallow depth of 7.5 km and severe shaking in an area of 4,000 square kilometers was assigned a maximum intensity of VIII on the China seismic intensity scale. Three people were killed and 146 injured when the earthquake struck Lu County,

Luzhou Luzhou (; Sichuanese Pinyin: Nu2zou1; Luzhou dialect: ), formerly transliterated as Lu-chou or Luchow, is a prefecture-level city located in the southeast of Sichuan Province, China. The city, named Jiangyang until the Southern and Northern Dyna ...

, Sichuan Province. At least 36,800 buildings were affected, 7,800 of them seriously damaged or completely destroyed, causing about a quarter of a billion dollars worth of damage.

Tectonic setting

The active

plate tectonic Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

s of the Sichuan Basin is dominated by the north–south

continental collision In geology, continental collision is a phenomenon of plate tectonics that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains prod ...

of the Indian Plate and Eurasian Plate. As the Indian Plate collides along a

convergent plate boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...

known as the Main Himalayan Thrust, it being of continental crust does not subduct, rather it plows into the Eurasian Plate. This process severely deforms the Eurasian Plate, uplifting the crust, forming the Tibetan Plateau. The force of the Indian Plate converging pushes the Tibetan Plateau east, towards the Sichuan Basin, forming another zone of collision. This collision and resulting crustal deformation of the Eurasian Plate is accommodated by the

Xianshuihe fault system The Xianshuihe fault system is a major active sinistral (left-lateral) strike-slip fault zone in southwestern China, at the eastern edge of the Tibetan Plateau. It has been responsible for many major earthquakes, and is one of the most seismically ...

, Kunlun Fault, Altyn Tagh fault, and Longmenshan Fault. The presence of active faults in Sichuan makes the region vulnerable to damaging earthquakes. The deadly 2008 Sichuan earthquake occurred due to a thrust fault

rupture Rupture may refer to: General * Rupture (engineering), a failure of tough ductile materials loaded in tension Anatomy and medicine * Abdominal hernia, formerly referred to as "a rupture" * Achilles tendon rupture * Rupture of membranes, a "wate ...

on the Longmenshan Fault.

Earthquake

The

China Earthquake Networks Center The China Earthquake Networks Center (CENC; ) is an institution under the China Earthquake Administration The China Earthquake Administration (CEA), () is mandated by the ''Law of the People's Republic of China on Protecting Against and Mitigating ...

placed the epicenter of the quake in Lu County, Sichuan and recorded its magnitude at 6.0. Meanwhile, the China Earthquake Administration (CEA) placed the magnitude at 5.3. The U.S. Geological Survey (USGS) recorded the event at 5.4 or 5.9. A maximum

seismic intensity Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake. They are distinguished from seismic magnitude scales, which measure the magnitude or overall stren ...

of VIII was assigned Sichuan Earthquake Administration and CEA. It was felt with weaker intensities by residents as far as

Chengdu Chengdu (, ; Simplified Chinese characters, simplified Chinese: 成都; pinyin: ''Chéngdū''; Sichuanese dialects, Sichuanese pronunciation: , Standard Chinese pronunciation: ), Chinese postal romanization, alternatively Romanization of Chi ...

. The

focal mechanism The focal mechanism of an earthquake describes the deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is ...

solution by both theUSGS and CEA indicated shallow reverse faulting at a depth of 7.5 or 6 km. A fault plane with a northwest–southeast striking structure due to northeast–southwest compression within the Eurasian Plate. An official at the Sichuan Seismological Station said the earthquake did not occur on the same fault as the 2008 event, adding that it was on the Huayingshan Fault Zone. The Huayingshan Fault Zone is much longer than the Longmenshan Fault, at 600 km in length, and is one of the largest faults in the Sichuan Basin. The fault has a northeast strike and dip at angles of 30° to 70°. The fault has a slip sense of sinistral

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and thrust.

Impact

The earthquake caused the collapse of over 1,400 houses, severely damaged 6,400 houses, and slightly damaged 29,000 houses. The majority of the homes damaged were old and of poor construction quality. Newer buildings withstood the tremor better as they were improved after the 2008 Sichuan earthquake, which killed nearly 90,000 and left over 18,000 missing. The quake damaged a warehouse in Lu County which led to the loss of 150 tons of liquor. Power outages were caused by the earthquake which disrupted power supplies and affected at least 20,000 homes. Telecommunication services ceased due to damage at 106 facilities and broken cables. Three high-speed rail services were temporarily suspended at Lu County as a result. The collapse of many homes in Lu County severely damaged a number of gas pipelines, affecting 678 families. Damage was reported at 42 reserviors, 10 embankments, 32 irrigation projects, and nine water supply centers. A small landslide occurred at Yuchan Mountain, partially burying the road along its slopes. Officials at the Chengdu University of Technology said there is a low risk of landslides occurring in the affected areas.

Casualties

The collapse of prefabricated buildings resulted in the deaths of two individuals. The first victim was an elderly man in his 70s who died after bricks fell onto him in his home. Another woman died when the prefabricated panels of her home fell on her. A third death was confirmed the following day as a woman in her 70s. Another 146 people were treated for injuries, at least three of them were in critical condition. Over 70,000 people were evacuated for medical treatment or temporary housing.

Response

Within five seconds of detection by seismic instruments, the

earthquake early warning An earthquake warning system or earthquake early warning system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for notifying adjoining regions of a substantial earthquake while it is in progress ...

system issued a warning via radio, television, and other means of

broadcast Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...

. Apps like

Sina Weibo Sina Weibo (新浪微博) is a Chinese microblogging ( weibo) website. Launched by Sina Corporation on 14 August 2009, it is one of the biggest social media platforms in China, with over 582 million monthly active users (252 million daily acti ...

and Alipay also provided advanced warning to users several seconds before shaking could be felt. More than 7,400 armed police and firefighters, 304 vehicles, and 95 rescue equipment such as patrol boats, and excavators were dispatched by Lu County to carry out rescue and relief works. The Luxian No.2 Middle School and Jiuquhe Park were used to temporarily facilitate the relocation of affected residents. Some 2,500 tents, 20,700 folding beds, 20,600 blankets and over 10,000 household items were provided to survivors. The Sichuan government 50 million yuan in allocation to disaster relief efforts, temporary shelter, patient transportation and resettlement and medical treatment.

References