Tsunami warnings across the Pacific | BBC Newscast

Key Concepts:

• Earthquake magnitude (Moment Magnitude Scale vs. Richter Scale)
• Mega thrust earthquakes and subduction zones
• Tsunamis: generation, propagation, and warning systems
• Seismic and volcanic activity links
• Stress field changes after earthquakes
• Building resilience and urban planning in earthquake-prone areas

1. Earthquake in Russia and Tsunami Warnings

• An 8.8 magnitude earthquake struck the Kamchatka Peninsula in the far east of Russia on Monday night.
• This triggered tsunami warnings across the Pacific, including Japan, Hawaii, and the west coast of the USA.
• As of Tuesday afternoon, many warnings were downgraded, but vigilance remained.
• Breaking news of a volcanic eruption in the same region added to concerns.

2. Understanding the Earthquake

• The earthquake is considered one of the largest since modern records began in the early 20th century.
• It occurred at a plate boundary where two plates are moving towards each other, with one subducting (sinking) beneath the other.
• This type of event is called a "mega thrust" earthquake, where plates get stuck for long periods and release energy suddenly.
• Mega thrust earthquakes under the sea can displace large volumes of water, causing tsunamis.
• The earthquake is rated the sixth largest since 1900, when modern seismology began.
• The 2004 Sumatra-Andaman earthquake and the 2011 Japan earthquake were also mega thrust events.
• Large earthquakes require faults that are hundreds or thousands of kilometers long.

3. Magnitude Scales: Moment Magnitude vs. Richter

• The Richter scale is an older scale that measures the amplitude of shaking at a fixed distance from the epicenter.
• The Richter scale saturates for very large earthquakes and is not suitable for measuring them accurately.
• The moment magnitude scale is a more modern scale related to the area of the fault that slips and the amount of slip.
• In the 2011 Japan earthquake, the plates moved by 52 meters.
• For the Russian earthquake, the slip is estimated at 8-10 meters maximum.
• The moment magnitude scale is a better indicator of the energy released in an earthquake.
• For every point increase on the moment magnitude scale, the energy released increases by a factor of 32.

4. Tsunami Warning Systems and Impact in Japan

• The damage in the far east of Russia appeared minimal.
• The resulting tsunami wave was smaller and less damaging than initially feared.
• The interconnected network of seismometers and global warning systems allowed for hours of warning, enabling people to move to higher ground.
• In Japan, tsunami warnings affected around 1.9 million people.
• People evacuated beaches and low-lying areas, heading to higher ground, rooftops, or designated shelters.
• Waves as high as 1.3 meters hit the Japanese Pacific coast.
• The Fukushima area is particularly sensitive due to the 2011 triple disaster.
• The operating company of the Fukushima Daiichi Power Plant evacuated workers as a precaution, reporting no abnormalities.
• Japan has upgraded its disaster alert systems since 2011, providing faster and more updated information.

5. How Tsunamis Work

• Tsunamis are caused by a disruption of the seabed, which moves the water column above it.
• Subduction zones have deep trenches with a lot of water above the mega thrust faults.
• Earthquakes that rupture to shallow depths can move the seabed and disrupt the water column.
• The collapse of water creates tsunami waves that propagate in all directions.
• The sea may recede dramatically before a tsunami wave arrives, exposing the seabed.

6. Link Between Earthquakes and Volcanic Eruptions

• A volcanic eruption was reported in the far east of Russia after the earthquake.
• Earthquakes can change the stress field of the surrounding region.
• Stress triggering can cause other faults to slip more quickly or delay their failure.
• The Turkey-Syria earthquakes were an example of stress triggering.
• The extent to which stress can be transferred over large distances and affect volcanic events is uncertain.

7. Building Resilience and Urban Planning

• There is a vast difference in building quality and resilience to earthquakes worldwide.
• Japan invests in earthquake-resistant buildings due to frequent large earthquakes.
• Some subduction zones have not experienced large earthquakes recently, leading to less investment in building resilience.
• It is important to understand which subduction zones are capable of large earthquakes.
• Early warning systems for earthquakes are more difficult to develop than for tsunamis.
• It's not earthquakes that kill people, it's falling buildings.
• Urban planning and building design have a significant impact on keeping people safe.
• Buildings in Japan can move on their foundations with the movement of the earth.

8. Conclusion

The 8.8 magnitude earthquake off the coast of Russia triggered widespread tsunami warnings, highlighting the interconnectedness of the Pacific region and the importance of effective warning systems. While the immediate impact appeared less severe than initially feared, the event underscored the immense power of tectonic forces and the ongoing need for research into earthquake prediction and building resilience. The discussion emphasized the complexities of magnitude scales, tsunami generation, and the potential links between seismic and volcanic activity, as well as the critical role of urban planning in mitigating earthquake risks.