TAIPEI (Taiwan News) — In the wake of two powerful earthquakes over magnitude 5.0 on Tuesday morning (Feb. 9), a Central Weather Bureau (CWB) seismologist said they could be a precursor to a much larger quake of up to magnitude 8.5.
Taiwan was struck by magnitude 5.5 and 5.7 earthquakes only two minutes apart early this morning (Feb. 9), sending shockwaves across the country, according to the CWB. The first earthquake, a magnitude 5.5, struck at 12:56 a.m. 73 kilometers east-southeast of Yilan County Hall at a focal depth of 69.3 km, while the second, measuring 5.7 on the Richter scale, struck a mere two minutes later at 12:58 a.m. 47.9 km southeast of Yilan County Hall at a focal depth of 23.9 km.
Chen Kuo-chang (陳國昌), director of the CWB's Seismology Center, on Tuesday was cited by Liberty Times as saying that Taiwan has already seen eight earthquakes in excess of 5.0 on the Richter scale this year. He said that the majority of these quakes took place in a subduction zone near the Hoping Basin.
Chen said that there was a higher frequency of earthquakes in this area last year as well. He said that there are two explanations for this: First, frequent occurrences are very good because energy is constantly being released, preventing a major earthquake. Second, in the past, large earthquakes occured near a subduction zone or trench, and quakes with a magnitude of 8.5 or larger historically had many foreshocks.
He pointed out that the magnitude 5.7 earthquake on Tuesday marks the eighth one with a scale of 5.0 or higher this year. He said that the two that struck that morning were caused by the same subduction zone and are currently considered aftershocks of the magnitude 6.1 temblor that struck off the northeast coast of Taiwan on Feb. 7.
In reference to foreshocks in recent history, Chen said that the 2011 Tōhoku earthquake, which registered a 9.0 on the Richter scale, was preceded by a magnitude 7.7 quake seven days prior. At the time, experts thought that it had been the primary temblor, only to witness a far more terrifying and catastrophic earthquake a week later.
Therefore, Chen advised that seismologists should closely monitor sudden clusters of quakes in the same area. He said that in the case of these recent quakes off the northeast coast of Yilan, the CWB will continue to closely observe the situation.
In addition, when asked why there were no alert messages sent when the earthquakes occurred this time around, Chen said that the magnitude 5.5 quake did not meet the standard for an earthquake warning. As for the second earthquake, he said that there were some errors in the estimation of the size at the time, and it was not picked up by the alert system.
He apologized that an alert message was not sent this time around and pledged that the notifications will be more accurate in the future. Chen said that there are many organizations involved in changing the mobile phone broadcasts, which must follow the procedures and approval of the Central Disaster Prevention and Response Council, and he estimated that a new messaging system will be in place by the second half of the year.