earthquakes anyone?

 We haven't had any major earthquakes in our area since we moved here, but we did lose out internet from an earthquake near Taiwan awhile back.

The main danger is the Manila trench and the Philippine trench, although a fault line does come right thru our area and our last big earthquake was in 1990,  

 

So I asked Grok what would happen if there was a major earthquake 

 The Manila Trench, west of Luzon, Philippines, is a major subduction zone where the Sunda Plate subducts beneath the Philippine Mobile Belt. Earthquakes along this trench can generate tsunamis, potentially causing significant damage to Luzon’s coastal areas, including Metro Manila.

=......Studies suggest that a large earthquake (magnitude 8.5–9.2) along the Manila Trench could produce tsunamis with waves up to **10 meters** high, impacting over **800 kilometers** of Luzon’s western coastline, including Metro Manila....  ...

In December 2024, PHIVOLCS warned that a magnitude 8.4 earthquake in the trench near Ilocos Sur could produce waves up to **14.7 meters**, reaching northern Luzon’s coast in as little as **2 minutes**.

**Metro Manila**: Low-lying coastal cities like Valenzuela, Navotas, Malabon, Manila, Pasay, Las Piñas, and Parañaque are highly vulnerable to flooding from tsunami waves. The Pasig River could channel waves inland, potentially flooding areas like Malacañang Palace and the Pandacan fuel depot....

 

**Western Luzon**: Provinces such as Ilocos Norte, Ilocos Sur, La Union, Pangasinan, Zambales, and Bataan face significant risk due to their proximity to the trench. 

**Other Regions**: Tsunamis could also affect countries around the South China Sea, including Taiwan, southern China, Vietnam, and Malaysia, though Luzon would bear the brunt.,,,

 

*Historical Context**: - Tsunamis in the Philippines are rare but devastating. The 1994 Mindoro tsunami (magnitude 7.1) caused 38 deaths with waves up to **8.5 meters**. The 1976 Moro Gulf tsunami (magnitude 8.1) killed around **8,000 people** with **9-meter waves**, though it was caused by the Cotabato Trench.[],,,    -

 

No major tsunamis from the Manila Trench have been recorded in recent history, but geological evidence suggests past basin-wide tsunami events, possibly from a magnitude 9.0+ earthquake with a rupture up to **1,000 km** long. (https://nhess.copernicus.org/articles/19/1565/2019/) ###

Vulnerability Factors - **Population Density**: Metro Manila’s high population and urban density increase the risk of casualties and economic loss. -

 

**Low-Lying Areas**: Many coastal areas have elevations below 4 meters, making them prone to flooding.... 

 

**Infrastructure**: Poorly built structures and soft sediment in areas like Pampanga amplify damage from ground shaking and tsunamis.[](https://en.wikipedia.org/wiki/2019_Luzon_earthquake) -

 

**Proximity to Trench**: The Manila Trench is only ~100–200 km from Luzon’s coast, leaving little time for evacuation....

 

Recent Events - On **January 20, 2025**, a magnitude 5.5 earthquake struck offshore between Mindoro and Luzon, felt in Metro Manila, but caused **no significant damage** or tsunami. This event highlights the region’s seismic activity but was too small to generate a tsunami.[]....

 

Conclusion A major Manila Trench earthquake could trigger a catastrophic tsunami, with waves up to 10–14.7 meters flooding Luzon’s western coast, particularly Metro Manila and northern provinces. Damage could range from hundreds of destroyed buildings and casualties in a moderate scenario to widespread devastation in a worst-case magnitude 9.0+ event. While no such tsunami has occurred recently, the region’s tectonic setting and historical evidence underscore the need for preparedness. For more details on tsunami risks, visit [PHIVOLCS](https://www.phivolcs.dost.gov.ph)  (https://en.wikipedia.org/wiki/Manila_Trench)

a lot of the damage in the recent Burma earthquake was from shoddy workmanship  and substandard rebars and concrete.

We are required to reinforce all our construction with rebars, so if the concrete shatters, the metal rods will keep the blocks in place. But with corruption, there is no guarantee that all the buildings will have proper construction and of course in a major earthquake, or with a major tsunami, buildings could collapse or be flooded.

one of the scandals in the recent Burmese earthquake was a new building that collapsed due to shoddy materials, and they are blaming the Chinese company that did the construction.

this is not the only time this happened: in China there was a big scandal after a 2008 earthquake. And poor Chinese construction is so common that they even have their own Wikipedia page: Tofu Dreg project.

I can believe it. Ten years ago, the mayor covered our drainage ditches with concrete plates, and they are all deteriorating/crumbling, and in two areas heavy trucks have collapsed into the drainage ditches because the coverings gave way, and had to be towed out.

So anyway, China is still destroying the sea beds in the West Philippine sea and presumably is using their wonderful tofu concrete to do so. So what would happen if the Manila plate off the west coast had an earthquake?

I asked Grok and they said the islands would probably survive the shaking but not the secondary tsunami.

Full answer below:

would an earthquake here destroy China's artificial islands in the west Philippine sea? Grok answers:

An earthquake along the Manila Trench could potentially impact China's artificial islands in the South China Sea, but whether it would "destroy" them depends on several factors, including the earthquake's magnitude, depth, location, and the structural integrity of the islands....

in other words, good construction might survive, but maybe not tofu buildings. 

... Manila Trench and Earthquake Potential The Manila Trench is an active subduction zone west of the Philippines, where the Sunda Plate subducts beneath the Philippine Mobile Belt. It is capable of generating significant earthquakes, with studies suggesting potential magnitudes ranging from Mw 8.5 to Mw 9.2, and in extreme scenarios, up to Mw 9.35. Such events could trigger tsunamis, which pose a greater threat to low-lying artificial islands than the earthquake's ground shaking alone, given the distance between the trench and the islands.

China's Artificial Islands China has constructed artificial islands in the South China Sea, primarily in the Spratly and Paracel Islands, by dredging and reclaiming land on coral reefs. These islands, such as Mischief Reef, Subi Reef, and Fiery Cross Reef, host military infrastructure, including airstrips, radar stations, and missile emplacements.

They are built on shallow reefs, making them vulnerable to sea-level changes, erosion, and extreme oceanic events like tsunamis.

 

The islands cover approximately 3,200 acres across seven Spratly features, created between 2013 and 2017. 

Potential Impact of an Earthquake Ground Shaking: The artificial islands are located hundreds of kilometers from the Manila Trench (e.g., Mischief Reef is roughly 200 nautical miles west of Manila). At this distance, the ground shaking from even a large earthquake (e.g., Mw 9.0) would likely be attenuated, causing minimal direct structural damage to the islands. However, the loose, unconsolidated sediment used in reclamation could amplify local shaking or lead to liquefaction, potentially destabilizing structures.

Liquification is where tremors cause clay beneath the buildings to liquify, and was a major problem in the Japanese 1995 Kobe earthquake. 

Tsunami Risk: The greater threat comes from a potential tsunami triggered by a megathrust earthquake. Studies indicate that a Mw 9.0+ earthquake along the Manila Trench could generate tsunami waves up to 10 meters high, impacting coastlines and islands in the South China Sea, including the Spratlys. ...

Inundation: A tsunami could flood the artificial islands, damaging infrastructure like runways, barracks, and radar installations... 

 

Historical Precedent: Geological evidence from ~1000 years ago (circa 1000–1064 CE) indicates a basin-wide tsunami in the South China Sea, likely caused by a Manila Trench megathrust event, with deposits found on islands like the Xisha (Paracel) and Badoc. This suggests that the Spratly Islands could also be affected.

 

Structural Vulnerabilities: The artificial islands are built on reclaimed coral reefs, which lack the geological stability of natural landmasses. The unconsolidated sediment and shallow foundations make them susceptible to erosion, subsidence, and wave damage.

 Environmentalists have noted that dredging has already damaged coral ecosystems, potentially weakening the islands' natural barriers against waves. A tsunami could exacerbate this, washing away loose material and undermining structures.... 

 

 longer post here