Earthquakes and Tsunamis: Understanding the Connection

Earthquakes and tsunamis are natural disasters that are sometimes closely connected through a cause-and-effect relationship. Earthquakes result from the movement of the Earth's tectonic plates beneath its surface, while tsunamis are often triggered by underwater earthquakes, particularly those that occur beneath or near the ocean floor. However, other events such as volcanic eruptions, landslides, and, in rare cases, meteorite impacts, can also lead to tsunamis triggering. Understanding these connections is crucial for both scientific research and efforts to mitigate the impact of these natural disasters on coastal communities.

In this blog, we will dive deep into the geological processes that lead to earthquakes and consequently tsunamis, a few case studies, as well as science and technology roles.

Geological Processes of Earthquakes

The Earth is divided into four main layers: the inner core, outer core, mantle, and crust. The crust and the upper mantle create a thin layer on the Earth's surface. However, this layer isn't a single piece; it's like a puzzle made up of many pieces covering the Earth. These puzzle pieces are always on the move, sliding past and colliding with each other. We call these pieces tectonic plates and the borders where they meet are called plate boundaries. These plate boundaries have many faults and most of the world's earthquakes occur along these faults. Because the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Eventually, when the plate has moved enough, the edges unstick at one of the faults, causing an earthquake.

Picture 1: Structure of the Earth. Source here.

When the edges of faults are stuck together, and the rest of the block is trying to move, a lot of energy gets stored up. This energy is like the power that would make the blocks slide past each other. Eventually, when the moving force is strong enough to overcome the rough edges' friction, the stuck parts unstick and all that stored energy is let out. This energy spreads out from the fault in all directions as seismic waves. As these seismic waves travel through the Earth, they shake it and when they reach the Earth's surface, they shake the ground.

We also know submarine, undersea, or underwater earthquakes, which is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean and can trigger tsunamis.

Understanding Tsunamis

Tsunamis originate from abrupt movements of the seafloor, typically occurring when a fault on the ocean floor ruptures, resulting in a significant earthquake. The displacement of the seafloor triggers a corresponding movement in the overlying water, giving rise to waves that pass through the open ocean at high speeds. As these waves approach shallower waters, their pace decreases, causing an increase in their height.

The process of tsunami formation due to submarine earthquakes is the following:

1. An underwater earthquake occurs: When tectonic plates beneath the Earth's surface shift or collide, earthquakes might be triggered by this process. If this seismic activity occurs beneath the ocean, it possesses the potential to displace a significant volume of water.

2. Dynamics of water displacement: The abrupt movement of the Earth's crust during an underwater earthquake induces a swift displacement of water. This displacement, in turn, can give rise to a sequence of powerful waves on the ocean surface.

3. Tsunami formation: The waves instigated by the underwater earthquake transform into a tsunami. Differing from conventional ocean waves, tsunamis exhibit considerably longer wavelengths and the ability to travel vast distances at notable speeds across open ocean waters.

Picture 2: Tsunami. Source here.

Tsunamis are commonly categorized as either local or distant, determined by the proximity of the tsunami's source and its potential landfall. Tsunamis originating close to the coast, known as local tsunamis, stem from sources near the coast, often reaching land in under an hour and posing a greater risk due to limited warning time. In contrast, distant tsunamis arise far from the coast, creating more time for issuing and responding to warnings. However, not all tsunamis exhibit uniform behavior and the impact on coastlines can vary significantly. A tsunami's size in one location may differ drastically just a few miles away.

The velocity of a tsunami is influenced by ocean depth. In the expansive depths of the ocean, tsunamis are inconspicuous but can reach speeds exceeding 500 mph, akin to a jet plane. Upon nearing shallow waters near the coast, their speed diminishes to approximately 20 or 30 mph, still outpacing the usual person running.

As waves slow down, their height can increase and currents become more forceful. While most tsunamis measure less than 3 meters (10 feet) in height, in extreme scenarios, they can surpass 30 meters (100 feet). Occasionally, before the water reaches the land, it recedes abruptly, unveiling the ocean floor, reefs, and fish, akin to an unusually low tide. Additionally, tsunamis can traverse rivers and streams leading to the ocean, with a substantial one capable of flooding coastal areas over a mile inland.

The sequence of waves, involving flooding, rapid drainage, and subsequent re-flooding, may persist for hours. The intervals between waves vary from five minutes to two hours. Notably, the initial wave reaching the shore may not be the largest or the most destructive. Predicting the duration of a tsunami, the number of waves, or the time gaps between them can be very challenging.

Tsunami Damage

Tsunamis can be very dangerous for people living near the coast and their property. These big waves come fast and can flood the land, causing a lot of harm and damage. The powerful currents generated by tsunamis can wreak havoc on boats, vehicles, and buildings, posing a big threat to both structures and human lives. Living near the coast can expose individuals to significant risks due to the potential danger of tsunamis. These massive waves move swiftly and can flood the land, resulting in substantial harm and damage. The powerful currents unleashed by tsunamis can wreak havoc on boats, vehicles, and buildings, representing a substantial threat to both structures and human lives.

The danger persists even after the initial impact, as the decaying water can be just as harmful. During this phase, the tsunami carries debris and individuals back to the sea, adding to the overall risk. The aftermath of flooding and treacherous currents can extend for days, weeks, or even months, further amplifying the hazards.

It's crucial to note that even smaller tsunamis present risks, with strong currents posing threats to swimmers, potentially causing injuries and drowning. Harbors are vulnerable, as boats can sustain damage or be destroyed. Awareness and preparedness are paramount in mitigating the dangers associated with tsunamis.

Picture 3: Rescue workers and residents of Sumatra after the destructive 2004 Sumatra earthquake and tsunami. Source here.

Case Studies: Notable Earthquake-Tsunami Events

While tsunamis occur less frequently than other natural disasters, historical data reveals occurrences of destructive tsunamis triggered by earthquakes, resulting in extensive damage:
1) 2004 Indian Ocean earthquake and tsunami,
2) 2011 Tōhoku earthquake and tsunami,
3) 2005 Nias-Simeulue earthquake and tsunami,
4) 2018 Sulawesi earthquake and tsunami, and
5) 1906 San Francisco earthquake and tsunami.

1) The 2004 Indian Ocean M9.1-9.3 earthquake and tsunami on the 26^th of December 2004, is considered one of the deadliest natural disasters in recorded history. A massive earthquake that struck off the west coast of northern Sumatra generated a powerful tsunami that affected multiple countries bordering the Indian Ocean. The death toll exceeded 230,000 people.
2) The 2011 Tōhoku M9.0 earthquake and tsunami on the 11^th of March 2011 struck off the east coast of Japan and triggered a devastating tsunami. The tsunami waves reached heights of up to 40 meters (131 feet) in some areas, causing widespread destruction and resulting in over 15,000 fatalities.
3) The 2005 Nias-Simeulue M8.7 earthquake and tsunami occurred on the 28^th of March 2005, near the island of Nias off the western coast of Sumatra, Indonesia. While the resulting tsunami was smaller than the one in 2004, it still caused significant damage and loss of life.
4) A series of earthquakes occurred on the 28^th of September 2018 in Sulawesi, including the 2018 Sulawesi M7.5 earthquake, which triggered a destructive tsunami. The disaster led to widespread devastation in the city of Palu and its surrounding areas, with thousands of casualties.
5) The 1906 San Francisco M7.8 earthquake and tsunami on the 18^th of April 1906 struck off the coast of northern California, causing widespread damage in San Francisco. While not primarily known for the tsunami it generated, the event resulted in significant destruction and loss of life.

Picture 4: Tsunami generated by the 2011 Tōhoku earthquake. Source here.

The destructive force of tsunamis extends far beyond the initial surge of water, reaching into the fabric of societies and ecosystems. Through understanding the complexities of tsunami dynamics and their impact, we gain the knowledge necessary to adapt and safeguard our coastal areas.

Human and Environmental Impact of Earthquakes and Tsunamis

Both earthquakes and tsunamis have immediate and long-term effects on human settlements and the environment. Understanding and addressing these impacts involves a comprehensive approach that encompasses emergency preparedness, recovery strategies, and sustainable development practices to minimize the vulnerabilities of communities in seismic-prone regions.

Tsunamis can lead to sudden flooding of coastal areas. The rapid rise in water levels can submerge low-lying regions, causing immediate destruction. Furthermore, the power of a tsunami can result in the destruction of ports, coastal structures, and other infrastructure in the vicinity of the shoreline. The impact is often more severe in areas with inadequate preparedness measures. Tsunamis can also result in a high number of casualties, particularly in densely populated coastal areas since the sudden and forceful nature of these waves leaves little time for people to evacuate to safer ground. However, the immediate effects extend beyond human settlements to marine ecosystems. Tsunamis can disrupt and damage coral reefs, mangroves, and other coastal habitats, affecting marine life.

Areas hit by strong tsunamis can experience a big long-term impact as well. For example, rebuilding coastal areas after a tsunami involves significant economic resources. Industries such as fisheries and tourism may experience long-term setbacks, affecting the livelihoods and well-being of communities over the long term. Additionally, tsunamis' impact on coastal ecosystems can persist for years. The deposition of debris and changes in sedimentation can alter the structure of coastal habitats, impacting both terrestrial and marine biodiversity. Long-term recovery efforts often focus on enhancing the resilience of communities to future tsunamis. This includes the development of tsunami early warning systems, improved evacuation plans, and sustainable land-use practices.

Tsunami recovery and reconstruction present numerous challenges due to the widespread and often catastrophic nature of the impact. Addressing these challenges requires coordinated efforts from governments, international organizations, and local communities. Balancing the need for speed with the necessity of ensuring long-term resilience poses a considerable challenge.

Conclusion

​Delving into the interconnected realm of earthquakes and tsunamis this blog has shown the relationship between these natural phenomena. The seismic forces beneath the Earth's surface can trigger not only ground-shaking tremors but also often devastating oceanic waves known as tsunamis.​

As witnessed in historical events and analyzed through scientific research, the synergy between these phenomena demands a multi-faceted approach to mitigation and response. In the face of such powerful forces of nature, fostering a global culture of preparedness, research, and cooperation is paramount. By unraveling the complexities of the earthquake-tsunami connection and disseminating this knowledge, we empower communities to navigate the challenges posed by these events with greater resilience and adaptability.

As we reflect on historical events and delve into scientific research, it's clear that addressing the synergy between earthquakes and tsunamis requires collective action. Let's cultivate a global culture of preparedness, research, and cooperation. Your involvement can make a difference—spread awareness, support research initiatives, and encourage community resilience efforts. Together, we can navigate the challenges posed by these events with greater strength and adaptability.

Sources:
1) National Weather Service. About Tsunamis. Accessed on 15-Nov-2023. Available at: https://www.weather.gov/safety/tsunami-about
2) USGS. The Science of Earthquakes. Accessed on 16-Nov-2023. Available at: https://www.usgs.gov/programs/earthquake-hazards/science-earthquakes
3) USGS. What are the Effects of Earthquakes? Accessed on 5-Nov-2023. Available at: https://www.usgs.gov/programs/earthquake-hazards/what-are-effects-earthquakes
4) Sms Tsunami Warning. Tsunamis: the effects. Accessed on 15-Nov-2023. Available at: https://www.sms-tsunami-warning.com/pages/tsunami-effects