May 20, 2013 – KAMCHATKA – A massive earthquake swarm has occurred in the region of Petropavlovsk-Kamchatskiy, Russia. More than 20 earthquakes have struck the region in the last 22 hours- the strongest of which was a 5.9 magnitude earthquake, which rattled the seafloor at a depth of 16.5 km deep. The latest seismic flare-up along this region reflects growing agitation on one of the planet’s largest tectonic plates- the Pacific plate. Increasing seismic volatility along this region of Kamchatka could have serious ramifications for every tectonic plate that comes into contact with the Pacific plate- from the South Pacific to South America. A similar, more intense earthquake swarm occurred along the periphery of the Pacific Plate near the Santa Cruz Islands in February of this year. Is the Pacific plate on the verge of a large-scale change?
The geology of the region: The Kuril-Kamchatka arc extends approximately 2,100 km from Hokkaido, Japan, along the Kuril Islands and the Pacific coast of the Kamchatka Peninsula to its intersection with the Aleutian arc near the Commander Islands, Russia. It marks the region where the Pacific plate subducts into the mantle beneath the Okhotsk micro-plate, part of the larger North American plate. This subduction is responsible for the generation of the Kuril Islands chain, active volcanoes located along the entire arc, and the deep offshore Kuril-Kamchatka trench. Relative to a fixed North America plate, the Pacific plate is moving towards the northwest at a rate that increases from 75 mm/year near the northern end of the arc to 83 mm/year in the south. Plate motion is predominantly convergent along the Kuril-Kamchatka arc with obliquity increasing towards the southern section of the arc. The subducting Pacific plate is relatively old, particularly adjacent to Kamchatka where its age is greater than 100 Ma. Consequently, the Wadati-Benioff zone is well defined to depths of approximately 650 km. The central section of the arc is comprised of an oceanic island arc system, which differs from the continental arc systems of the northern and southern sections. Oblique convergence in the southern Kuril arc results in the partitioning of stresses into both trench-normal thrust earthquakes and trench-parallel strike-slip earthquakes, and the westward translation of the Kuril forearc. This westward migration of the Kuril forearc currently results in collision between the Kuril arc in the north and the Japan arc in the south, resulting in the deformation and uplift of the Hidaka Mountains in central Hokkaido. The Kuril-Kamchatka arc is considered one of the most seismically active regions in the world. Deformation of the overriding North America plate generates shallow crustal earthquakes, whereas slip at the subduction zone interface between the Pacific and North America plates generates interplate earthquakes that extend from near the base of the trench to depths of 40 to 60 km. At greater depths, Kuril-Kamchatka arc earthquakes occur within the subducting Pacific plate and can reach depths of approximately 650 km. -USGS
April 20, 2013 – SICHUAN, CHINA – A strong 6.6 magnitude earthquake hit a remote, mostly rural and mountainous area of southwestern China’s Sichuan province on Saturday, killing at least 203 people and injuring about 11,500 close to where a big quake killed almost 70,000 people in 2008. The earthquake, China’s worst in three years, occurred at 8.02 a.m. (0002 GMT) in Lushan county near Ya’an city and the epicenter had a depth of 12 km (7.5 miles), the U.S. Geological Survey said. The quake was felt by residents in neighboring provinces and in the provincial capital of Chengdu, causing many people to rush out of buildings, according to accounts on China’s Twitter-like Sina Weibo microblogging service. State media said 156 people had been confirmed dead with more than 5,500 injured. President Xi Jinping and Premier Li Keqiang said all efforts must be put into rescuing victims to limit the death toll. After arriving at the disaster zone by helicopter, Li directed earthquake relief efforts from a plaza in Longmen Township in Lushan, Xinhua said. Li asked that a road be opened to Baoxing County, one of the most affected by the earthquake, and that rescuers “act quickly” in their efforts, Xinhua quoted Li as saying. “The current most urgent issue is grasping the first 24 hours since the quake’s occurrence, the golden time for saving lives,” Xinhua news agency quoted Li as saying earlier. Xinhua said 6,000 troops were heading to the area to help with rescue efforts. State television CCTV said only emergency vehicles were being allowed into Ya’an, though Chengdu airport had reopened. Most of the deaths were concentrated in Lushan, where water and electricity were cut off. Pictures on Chinese news sites showed toppled buildings and people in bloodied bandages being treated in tents outside the hospital, which appeared only lightly damaged. Rescuers in Lushan had pulled 32 survivors out of rubble, Xinhua said. In villages closest to the epicenter, almost all low rise houses and buildings had collapsed, according to footage broadcast on state television. “We are very busy right now, there are about eight or nine injured people, the doctors are handling the cases,” said a doctor at a Ya’an hospital who gave her family name as Liu. The hospital was seeing head and leg injuries, she added. The China Meteorological Association warned of a possibility of landslides occurring in Lushan county on Saturday and Sunday, the agency said in a statement on its website. A resident in Chengdu, 140 km (85 miles) from Ya’an city, told Xinhua he was on the 13th floor of a building when he felt the quake. The building shook for about 20 seconds and he saw tiles fall from nearby buildings. Ya’an is a city of 1.5 million people and is considered one of the birthplaces of Chinese tea culture. It is also the home to one of China’s main centers for protecting the giant panda. “There are still shakes and tremors and our area is safe. The pandas are safe,” said a spokesman with Ya’an’s Bifengxia nature park, a tourism park that houses more than 100 pandas. Shouts and screams were heard in the background while Reuters was on the telephone with the spokesman. “There was just an aftershock, an aftershock, our office is safe,” he said. Numerous aftershocks jolted the area, the largest of which was magnitude 5.1. Sichuan is one of the four major natural-gas-producing provinces in China, and its output accounts for about 14 percent of the nation’s total. The U.S. Geological Survey initially put the magnitude at 7, but later revised it down. The devastating May 2008 quake was 7.9 magnitude. –
