City’s urban planning unfit to resist even moderate earthquakes

Location of the epicentre of two recent earthquakes and spatially related active faults (dashed lines) in the Zhuhai-Macau and surrounding areas

Macau’s urban infrastructure could not cope with even an earthquake of medium intensity, researchers have indicated to the Times, citing the apparent lack of earthquake-resistant structures across the city.
Asia’s gambling hub is missing earthquake mitigation in its urban planning as the city’s high-rise buildings, complex infrastructures, and urban and touristic facilities may not be able to withstand earthquakes.
Earth science experts contacted by the Times warned that there is a need to raise awareness about the earthquake tremors that have been felt recently in the city, adding that even though they are only tremors, the risks should not be underestimated.
Recent low-magnitude earthquakes in neighboring regions such as Guangdong Province have been barely registered in Macau.
Last week, a magnitude 2.2 earthquake was detected with the epicenter located approximately 21 kilometers southwest of Macau. Some netizens said on social media that they had felt the tremor. In general, the population can only notice seismic activity when magnitudes are above 2 to 3.
Ágata Alveirinho Dias, an associate professor from the Institute of Science and Environment at the University of Saint Joseph expressed her belief that while the region must expect low-magnitude earthquakes, there is an outside chance that more disastrous earthquakes could actually occur.
Dias, who is a geology expert, said that despite moderate levels of seismic activity in the city, the population must be prepared for the occurrence of low to moderate earthquakes with some frequency.
“Macau lies within an active seismic area (the Lianhuashan seismic zone) and is directly affected by the other ones. The seismic activity is, contrarily to what is believed, frequent but usually of low magnitude,” said Dias.
The probability of strong earthquakes (magnitude 8 or above) occurring is extremely low. Even magnitude 6 earthquakes are very rare for Macau, according to Dias.
“If a seismic activity of magnitudes 2 to 3 is almost undetectable for most people, and the damage is none or residual, the same is not true for magnitudes 4 to 6 earthquakes. They can cause significant impacts, particularly if the population and structures such as buildings and bridges are not prepared,” said Dias.
“There are some earthquake-proof buildings in Macau [such as] the Macau Tower and the Hong Kong-Zhuhai-Macau Bridge, but the majority of buildings, particularly ones in older residential areas, are likely to be unfit to resist even moderate earthquakes,” she added.
Since the city has changed dramatically in line with rapid economic growth, the large concentration of high-rise buildings, complex infrastructures, urban and touristic facilities, and a significant proportion of reclaimed land face potential seismic risks.
To answer whether the city is prepared to face a moderate earthquake, Dias believes that the recent small earthquake plays a significant part in educating the population on how to act during these events and encouraging the integration of earthquake mitigation in the city’s urban planning.
“If these small tremors could serve to promote population awareness and a rethinking of strategies that can help to mitigate the effect of a possible stronger earthquake, then, these small quakes are welcome,” said the expert.
Takashi Nakagawa, an associate professor at The University of Hong Kong’s Department of Earth Sciences said that the effects of earthquakes, even those that occur in nearby regions, should not be downplayed.
Nakagawa said that although the probability of moderate seismic activity occurring in Macau is low, the risk and the extent of damage is relatively high.
“Many Hong Kong and Macau people believe that the risk of an earthquake is low, which is a dangerous thought,” the academic told the Times.
“I would recommend people living here to learn the mechanism of the earthquake and its risks as soon as possible. Then they can prepare for the future impact from such events,” he added.
For example, study of the natural disaster should be incorporated into students’ textbooks in the two SARs, he suggested. That would help students to be better prepared to deal with earthquake hazards, should they occur.
“Students should learn more about natural hazards,” said Nakagawa. “Aside from flooding and extreme weather, students must also be briefed on seismic and volcanic activities and their risks. This is a good practice for their preparedness.”
The recent 2.2 magnitude earthquake was the second minor earthquake that was felt in the city this year.
The first was on January 5 with a 3.5 magnitude, which occurred in the seas under the administration of the Xiangzhou District in Zhuhai.
Larger-scale earthquakes were recorded several decades ago and were felt in Macau, including the 7.3 magnitude earthquake recorded on February 13, 1918 in Nan’ao, Guangdong.
The recent two earthquakes were generated by faults from the Lianhuashan seismic zone, however they were located in different faults. The latest one was due to the movement of the Nimenwan fault, whereas the previous earthquake had its epicentre in waters southeast of Macau and is spatially related to the Qi’ao-Guishan fault.
According to Nakagawa, the geologic map of Hong Kong, Macau, and Guangdong Province shows several faults but many of their activities are inactive.
However, they could be reactivated if the geologic setting changes due to the dynamics configuration of the Earth. According to the current geological feature, Hong Kong and Macau seem to be located in the stable plate.
On average, more than 10 earthquakes above magnitude 2 are recorded in Guangdong Province every month. During just one year, dozens of tremors can be recorded in the estuary of the Pearl River alone.
Dias explained that the theory of plate tectonics suggests the occurrence of most earthquakes, since they result from repeated accumulation and release of tension at the contacts between differentially moving plates.
The most damaging earthquakes occur along plate boundaries, which explains why stronger earthquakes are usually noted in regions on or adjacent to subduction zones such as Japan, Indonesia, Taiwan and the Philippines.
More than 90% of earthquakes have their origin at plate boundaries, however intraplate seismic events that take place far away from the plate boundaries, also occur.
“Although Macau is relatively close to major plate boundaries, such as the contacts between the Eurasian-Philippines plates and the Eurasian-Australian plates, it is located intraplate, that is, far from a direct influence of the boundaries movement between those plates,” explained Dias.
“This fact explains why seismic activity is weaker and less frequent than, for example, in Taiwan or Japan,” Dias added.

Earthquake risk map of coastal zone of Southeast China