Taiwan's Plate Tectonics and Seismic Activity

30-Second Overview

Taiwan is located at the convergent boundary where the Eurasian continental plate meets the Philippine Sea plate. The intense collision of these plates has resulted in Taiwan's unique geological structure and frequent seismic activity. Thirty-six active faults are distributed across the island; the western seismic zone features shallower epicenters but high population density, while the eastern seismic zone has deeper epicenters but frequent activity.

The Great Kensa Earthquake (Magnitude 7.3) of September 1999 was Taiwan's most severe modern seismic disaster; the fault map updated by the Geological Survey in 2021 forms the core basis for current disaster prevention planning. Taiwan ranks among the world leaders in earthquake density and is a crucial site for plate tectonics research.

Keywords: Plate Convergence, Active Fault, Seismic Zone, Shilin Fault, Orogeny

Why It Is Important

The Geological Background of Taiwan

Taiwan's existence itself is a geological marvel. Approximately 5 million years ago, Taiwan was an ocean; it only gradually rose above the sea surface after being squeezed northwestward by the Philippine Sea plate and colliding with the Eurasian continental plate. This intense geological process continues today, making Taiwan one of the best sites for studying plate tectonics.

The plate collision proceeds at a rate of 7–8 centimeters annually, causing the land surface of Taiwan to continuously rise, which makes earthquakes an inherent destiny of this island.

Living on a Dynamic Earth

For the Taiwanese people, earthquakes are part of daily life. From earthquake-resistant building codes to widespread disaster prevention education, Taiwanese society has developed a culture of coexistence with seismic risk. Understanding Taiwan's geological characteristics aids in disaster mitigation and deepens our appreciation for this land.

Following the Great Kensa Earthquake in 1999, Taiwan comprehensively revised its building seismic regulations, and its earthquake early warning system gradually upgraded to one of Asia's most advanced systems.

Plate Tectonics and Geological Context

Geographic Location at a Double-Plate Collision Zone

Taiwan is situated at one of the world's most active plate boundaries. To the west of Taiwan lies the stable Eurasian continental plate; to the east, there is the active Philippine Sea plate. These two plates are pushing against each other at a rate of about 7–8 centimeters per year—comparable to fingernail growth—which seems slow but possesses tremendous power.

Off the northeast coast of Taiwan, the Philippine Sea plate subducts beneath the Eurasian plate, forming the Ryukyu Trench; off the southeast coast of Taiwan, the reverse occurs, with the Eurasian plate subducting beneath the Philippine Sea plate, forming the Manila Trench. Taiwan is located in a transition zone where these two opposing subduction directions meet, resulting in an extremely complex geological structure.

Ongoing Orogeny (Mountain Building)

The formation of Taiwan's mountain ranges is an ongoing process. The Central Mountain Range is the most direct product of plate collision; most mountains exceeding 3,000 meters in altitude are concentrated here. Taiwan's orogeny is not uniform: the Central Mountain Range and the east rise by several millimeters to nearly one centimeter annually, while the western regions are relatively stable, with some coastal areas even subsiding.

This "asymmetric uplift" explains why eastern Taiwan has many high mountains while the west features plains and hills. Taiwan's landscape continues to evolve—the Taiwan we see today will be vastly different from the Taiwan of a million years ago or a million years hence.

Distribution of Seismic Zones in Taiwan

Western Seismic Zone: Shallow Threat with High Population Density

The western seismic zone covers the entire western part of Taiwan, extending from the Taipei Basin down to the Pingtung Plain. This seismic zone has several characteristics:

Shallow Epicenters: Most earthquakes occur at depths between 10 and 20 kilometers, belonging to crustal faulting. Although shallow quakes may not be massive in magnitude, they often cause strong ground motion and severe damage because of their proximity to the surface.

Complex Fault System: The western seismic zone is home to multiple active faults, including the Shilin Fault, Changhua Fault, and Xincheng Fault. These faults are mostly reverse faults, reflecting a compressional tectonic environment from east-west forces.

Immense Human Threat: Since about 80% of Taiwan's population lives in the western region, any large-scale seismic activity in the western zone could cause severe casualties and economic losses. The Great Kensa Earthquake of September 1999 is the clearest example.

Eastern Seismic Zone: Frequent Vibrations from Deep Subduction

The eastern seismic zone is mainly located off the east coast and on the eastern landmass, and its characteristics are distinctly different from the west:

Varied Epicenter Depths: It features earthquakes ranging from shallow events of a few kilometers to deep events reaching 300 kilometers, forming a seismically inclined distribution band—which is evidence of Philippine Sea plate subduction.

Extremely High Earthquake Frequency: The frequency of earthquakes in the east far exceeds that in the west; earthquakes of various sizes occur almost daily. However, because the population density is relatively lower, the impact of disasters is usually smaller.

Tsunami Risk: Large-scale earthquakes off the eastern coast can trigger tsunamis, posing a threat to the eastern coastal areas. The September 2022 Chishang Earthquake is a typical example of activity in the eastern seismic zone.

Northeastern Seismic Zone: A Symphony of Volcanoes and Earthquakes

The northeastern region of Taiwan, including the Greater Taipei area, has a unique seismic environment influenced by the expansion of the Okinawa Trough and volcanic activity. Although the Datun Volcanic Group is currently dormant, it still exhibits minor seismic activity, reminding us of the potential volcanic threat in northern Taiwan.

Distribution and Characteristics of Active Faults

Current Status of Active Faults

Taiwan has currently confirmed 36 active faults (according to the latest version from the Geological Survey and Mining Bureau in 2021) ¹, including the Milun Fault, Chishang Fault, and Shilin Fault. The old fault activity classification system has been unified and abolished; management is now conducted using geological sensitivity zoning mechanisms. The potential threat of earthquakes for each fault varies, which forms the core basis for disaster prevention planning.

Building Restrictions in Fault Zones

To reduce seismic disasters, the government imposes strict land-use controls on active faults. Within a 15-meter radius on either side of the fault trace (the "fault zone"), public land is completely prohibited from construction, and private land is restricted to buildings no taller than two stories or 7 meters. Although this regulation limits land development, it is critically important for ensuring public safety.

Lessons from the Shilin Fault

The Shilin Fault was the main rupture during the Great Kensa Earthquake of September 1999. It is about 105 kilometers long and generated a maximum vertical displacement of 8 meters during the earthquake, directly causing surface ruptures and building collapses. Post-earthquake research found that buildings within a 200-meter zone above and a 100-meter zone below the fault were most severely damaged, a finding that directly influenced subsequent revisions to building codes.

Major Modern Earthquake Events

The Kensa Earthquake (September 21, 1999)

At 1:47 AM on September 21, 1999, an M 7.3 earthquake occurred near Ji-ji Township in Nantou County, with a maximum seismic intensity of 7. This earthquake resulted in 2,415 fatalities and 11,305 injuries, causing over 100,000 buildings to collapse or partially collapse. The estimated direct economic loss exceeded NT$300 billion, making it the deadliest natural disaster in post-war Taiwan (the 1935 Hsinchu-Taichung Earthquake, which caused 3,276 fatalities, remains the worst of the 20th century). Surface ruptures along the Shilin Fault extended about 105 kilometers, with vertical displacements reaching 8 meters at certain locations. The Kensa earthquake prompted Taiwan to comprehensively revise its building seismic standards and significantly strengthen earthquake engineering research capabilities, laying the foundation for Taiwan's modern seismic defense system ².

The Hualien Earthquake (April 3, 2024)

At 7:58 AM on April 3, 2024, an M_L 7.2 / M_w 7.4 earthquake occurred off the east coast of Taiwan (offshore Hualien), which was the largest in magnitude since the Kensa Earthquake in 1999. The earthquake caused 18 fatalities and 1,155 injuries, with many buildings in Hualien City tilting severely. A large-scale landslide triggered by the earthquake buried several mountain hikers along the Shaka Trail, leading to a search and rescue operation that lasted several days. The initial earthquake warning system estimated the magnitude at 6.2; since Taipei and New Taipei did not reach the Intensity 4 threshold, no alarm was issued, making it a key case study for post-event review of the early warning system ³⁴.

Earthquake Monitoring and Early Warning Systems

Dense Monitoring Network

Taiwan has established one of the world's densest earthquake monitoring networks. The real-time seismic observation network operated by the Central Weather Administration’s Seismological Center expanded from 71 stations when it was founded in 1989 to over 170 real-time observation stations after the new generation network was activated in 2012, with an average monitoring point every 200 square kilometers ³. This dense network can determine the epicenter location and magnitude within 20–30 seconds of an earthquake.

Earthquake Early Warning System (EEW)

Taiwan's Earthquake Early Warning System (EEW) is one of Asia's most advanced systems. When a major earthquake occurs, the system issues an alert several to tens of seconds before the seismic waves arrive, providing precious evacuation time for the public. Although the warning time is limited, it holds critical disaster prevention value for high-speed trains and precision industrial equipment.

Strong Motion Real-Time Alert Service

The strong motion real-time alert service, launched in 2016, automatically issues alerts through television, radio, and mobile push notifications when the estimated intensity reaches Level 4 or higher. Taiwan is one of the nations that early established a national earthquake early warning system and is considered a pioneer in the Asian region.

Earthquakes and Taiwanese Society

Development of Seismic Resistant Building Technology

Taiwan has continuously improved its seismic resistant building technology through repeated seismic disasters. From early static seismic design to current base isolation and damping technologies, Taiwan's construction capabilities have reached world-leading standards. The Tuned Mass Damper (TMD) in Taipei 101 is a famous application of damping technology.

Formation of Earthquake Culture

The attitude of the Taiwanese people toward earthquakes is cautious yet composed. Drills for earthquake evacuation starting from elementary school, preparation of household emergency kits, and the reaction of "duck, cover, hold on" during an earthquake have all become part of Taiwanese culture.

The phrase "Taiwanese are not afraid of earthquakes" does not mean that Taiwanese disregard earthquakes; rather, it means that they have learned to coexist with seismic risk, reducing disaster risks through science and technology while respecting nature.

Contributions to International Earthquake Research

Taiwan's unique geological environment and rich seismic data attract seismologists from many countries to conduct collaborative research here. Taiwan's research findings on fault behavior and early warning systems are published in international journals and offer direct reference value for global disaster prevention practices.

Challenges Looking Ahead

New Threats from Climate Change

In recent years, scientists have found that climate change may affect seismic activity. Increased extreme rainfall can alter groundwater pressure, which in turn affects the stability of faults. Taiwan needs to incorporate these new risk factors into its earthquake disaster prevention planning.

The Dual Impact of Urbanization

Taiwan's urbanization process presents a dual impact: on one hand, the seismic performance of modern buildings has greatly improved; on the other hand, population and assets are becoming increasingly concentrated, meaning that potential losses increase significantly in the event of a major earthquake. Balancing development and safety is a long-term challenge facing Taiwan.

Opportunities from Technological Innovation

New technologies such as artificial intelligence, big data analysis, and the Internet of Things offer new possibilities for seismic research and disaster prevention. Taiwan is exploring the use of these technologies to improve earthquake prediction and early warning systems, making disaster prevention work more precise and effective.

References