On the 10th (local time), a magnitude 7.4 earthquake struck western Colombia, and with at least 111 confirmed dead, anxiety is spreading that the Ring of Fire in the Pacific earthquake belt may have turned active again.
Earlier, starting in June with the United States' California and Venezuela, powerful earthquakes linking key seismic zones occurred in quick succession in less than half a day all the way to off Iwate Prefecture, Japan. Then on the 28th of last month, a magnitude 7.1 earthquake by Japan Meteorological Agency standards struck Kumamoto, Japan, recording a maximum intensity of 7. However, experts said the global frequency of earthquakes has not deviated from the usual range, analyzing that the timing of strong quakes in several fault boundaries where earthquakes are common happened to overlap by chance.
The Colombian government said on the 10th that a magnitude 7.4 earthquake occurred 107 kilometers underground near San José del Palmar in western Chocó Department. Magnitude is a figure showing how much energy an earthquake releases. Each increase of 1 multiplies the energy by about 32 times. This quake is smaller than the Myanmar earthquake (7.7) in March last year that killed more than 5,400 people, but compared with the largest earthquake observed in Korea in 2016 in Gyeongju (5.8), it released about 250 times more energy. The Colombian Geological Survey assessed this quake as the strongest observed in the country in the 21st century.
Colombian President Abelardo de la Espriella said, "At least 111 people were killed and 87 were injured by this earthquake," and declared a national state of emergency. Near the epicenter, about 1,600 buildings were damaged, 61 of which collapsed completely. In Manizales, a famed coffee-growing area, the spire of the cathedral that symbolized the city toppled, and at Pereira Airport, a nearby transport hub, the ceiling fell and travelers took shelter. Colombia's aviation authorities simultaneously suspended operations at six airports in the west and began safety inspections of runways and buildings.
Chocó, close to the epicenter, is Colombia's poorest region, where most residents can travel only by boat or plane, so the full extent of the damage has not yet been tallied. Some areas remain out of contact because mobile networks have not yet been restored. Experts noted that the deeper the focus, the more surface shaking often diminishes, but this quake produced strong shaking, amplifying the damage. Susan van der Lee, a seismology professor at Northwestern University in the United States, told Reuters, "The epicenter of this quake was much deeper than the crust, so in theory the shaking should have been less, but in reality it produced very strong shaking," adding, "The magnitude itself was so large, and the epicenter was close to densely populated valley areas, which worsened the damage."
Colombia is originally one of the world's most earthquake-prone regions. John Macario Londoño, director of geohazard technology at the Colombian Geological Survey, told the Spanish daily El País on the 10th, "Colombia is a rare country where three plates—the South American Plate, the Nazca Plate, and the Caribbean Plate—meet all at once," adding, "At least 2,500 small earthquakes occur every month. Colombia is always shaking."
In Venezuela, which shares its eastern border with Colombia, two strong earthquakes struck 39 seconds apart on June 24, killing more than 6,300 people. This quake was recorded as the strongest to occur in Venezuela since 1900. In the Caracas metropolitan area, searches are still ongoing even now, nearly two months later.
According to the U.S. Geological Survey (USGS), seven hours before the magnitude 7.2 and 7.5 earthquakes in northern Venezuela, a magnitude 5.6 quake hit Northern California at 11:10 a.m. on the same day. Twenty-six minutes after the Venezuela quakes, a magnitude 7.2 earthquake struck off Iwate Prefecture, Japan, on the other side of the globe. With Japan's Kumamoto quake last month and Colombia's quake this month following in succession, concern grew that the entire "Ring of Fire" might have awakened.
However, experts analyzed that long-term USGS statistics make it hard to see this year as unusual. Based on records since 1900, the USGS says an average of 16 large earthquakes of magnitude 7 or greater occur worldwide each year. The actual annual counts swing widely, falling to six in 1989 but rising to 23 in 2010.
This year, in addition to the quakes mentioned above, there have been 10 magnitude-7-and-higher events: Malaysia 7.1 (Feb. 22), Tonga 7.5 (March 24), Vanuatu 7.3 (March 30), Indonesia 7.4 (April 1), the Philippines 7.8 (June 7), and Mexico 7.3 (July 17). If this pace holds, the year-end total is expected to stay around 16, similar to the average year.
The USGS called the phenomenon of more or fewer earthquakes during a given period "normal variability in occurrence rates," drawing a line that "frequent earthquakes themselves cannot be interpreted as a sign that a larger quake is imminent." As when flipping a coin many times there are stretches when heads comes up repeatedly, magnitude-7-class strong earthquakes, viewed year by year, tend to cluster within a few weeks and then go quiet for months, repeatedly.
The public tends to lump all earthquakes into the "Ring of Fire" or the Circum-Pacific orogeny, but actual analyses point out that each quake has subtle differences. Earth's surface is covered by several massive rock plates, and earthquakes occur concentrated along the boundaries where plates meet and push and collide. The well-known Ring of Fire is a plate-boundary belt encircling the Pacific in a horseshoe shape, and Japan, California, and Colombia's Pacific coast all fall along it. By contrast, the Venezuela quake that caused the most damage this year was an "outside-the-ring quake" that occurred along a separate boundary where the Caribbean Plate and the South American Plate meet.
One reason earthquake news seems much more frequent lately is advances in monitoring technology. As more instruments come online, even small quakes that used to be missed are recorded, and with faster communications, news of quakes on the other side of the world spreads in minutes. The National Earthquake Information Center under the USGS, which compiles global earthquake information, now detects about 20,000 quakes a year, an average of 55 a day. Experts added that when, as now, casualties occur in places like Japan, California, and Colombia—regions with large populations and high news exposure—it reinforces the impression that earthquakes are rising everywhere at once.