La Probabilité d’un Mégaséisme Augmente en ce Moment Même

Sympa

Les scientifiques surveillent de près les chances qu'un tremblement de terre mégasismique se produise bientôt. Ce sont les types de séismes les plus forts, causés lorsqu'une plaque tectonique glisse sous une autre, et ils peuvent entraîner des destructions massives et des tsunamis. En ce moment, certaines régions comme le nord-ouest du Pacifique, le Japon et l'Indonésie montrent une activité sismique accrue, ce qui pourrait signifier qu'une pression s'accumule sous terre. Les experts utilisent des données telles que de petites secousses, les mouvements du sol et les schémas historiques pour prédire la probabilité de ces séismes. Bien qu'il soit impossible de dire exactement quand ou où cela se produira, ils exhortent les gens dans les zones à haut risque à se préparer. Avoir un kit d'urgence, un plan de sécurité et rester informé pourrait sauver des vies lorsque le grand séisme frappera.  Animation créée par Sympa. ---------------------------------------------------------------------------------------- Musique par Epidemic Sound https://www.epidemicsound.com   Pour ne rien perdre de Sympa, abonnez-vous!: https://goo.gl/6E4Xna​ ---------------------------------------------------------------------------------------- Nos réseaux sociaux : Facebook: https://www.facebook.com/sympasympacom/ Instagram: https://www.instagram.com/sympa.officiel/  Stock de fichiers (photos, vidéos et autres): https://www.depositphotos.com https://www.shutterstock.com https://www.eastnews.ru ----------------------------------------------------------------------------------------  Si tu en veux encore plus, fais un tour ici:  http://sympa-sympa.com

Transcript

00:00A dreadful power lies underground, where the tectonic plates converge and where one forces the other to sink.

00:09This phenomenon manifests itself mainly in the Pacific and Indian Oceans.

00:13Over the centuries, the pressure accumulates, reaching a critical point until the awakening of the mega-earthquake.

00:19The earth is shaken with an intensity sometimes exceeding 9 on the magnitude scale, surpassing any other known earthquake.

00:28When the seabed is suddenly propelled upwards, a huge wave propagates in the water, generating a tsunami of a titanic force.

00:37These waves, called teletsunamis, cross the oceans, ready to devastate the coasts located thousands of kilometers away.

00:44Expanding over a thousand kilometers, the collapse gives the impression that the earth is not only shaking, but that it is literally tearing apart.

00:52This is what testifies to the power of a mega-earthquake.

00:56Those who are on their way will have to flee for their lives.

01:00Japanese authorities have recently issued their very first mega-earthquake warning.

01:05This warning was triggered by a violent shake on the edge of the Nankai underwater pit.

01:10Although most of the alerts were raised and the magnitude 7.1 earthquake caused little damage,

01:16shakes hit southwest Japan, slowing trains at high speed for safety reasons and affecting the movements of many travelers.

01:26However, vigilance remains in place against the threat of a mega-earthquake likely to occur in the Nankai pit in the decades to come.

01:34Under the Philippine Sea, a tectonic plate slowly sinks under Japanese territory, progressing a few centimeters per year.

01:42The last major earthquakes recorded in this region date from 1944 and 1946, each with a magnitude of 8.1.

01:51These earthquakes caused considerable destruction throughout the country.

01:55If a new mega-earthquake were to occur in the region, it could reach a magnitude between 8 and 9.

02:02Scientists still do not agree on the exact probability of this event, although it can be estimated up to 80%.

02:11On the other side of the Pacific, researchers from the US Geological Survey examined a critical zone located along the western coast of the United States.

02:19Known as the Cascadia Subduction Zone, it extends from northern California to northern Vancouver Island in Canada.

02:27Over the last 14,200 years, this region has experienced at least 30 major earthquakes, with an average frequency of one every 500 years.

02:37However, the Cascadia region has remained abnormally calm for a long time, which alarms experts.

02:43They suppose that the zone could be blocked, with tectonic plates stuck together accumulating immense pressure.

02:50A sudden rupture of part of the seabed could occur, causing a displacement of several meters.

02:56Although the main shake lasts only 5 minutes, it would cause a devastating tsunami lasting up to 10 hours.

03:04If this happened, it would be, according to experts, the worst natural disaster in the history of the country.

03:10In some areas, the ground of the hills could liquefy and behave like moving sands, causing the collapse of slopes, roads and bridges.

03:20About 620,000 buildings could be seriously damaged, or even collapse, including a hundred hospitals and 2,000 schools.

03:29Residents of the state of Washington could be forced to survive on their own on their essential needs, water, food and shelter, for two weeks.

03:40Scientists analyze the phenomenon of slow slides, where tectonic plates move imperceptibly over weeks or months,

03:48releasing an insufficient amount of energy to avoid a major earthquake.

03:53Each increase of one point on the magnitude scale multiplies the released energy by 40.

03:59Thus, it would take about 1 million small earthquakes per day, for 500 years, to equal the energy released by a single magnitude 9 earthquake.

04:08These small earthquakes could be revealed the premises of a major earthquake.

04:13To strengthen the surveillance of the Cascadia fault, experts proceed to a more detailed mapping and deploy more sophisticated maritime surveillance instruments.

04:22A funding of more than 10 million dollars allowed the installation of seismic sensors and underwater pressure gauges on an optical fiber cable off the coast of Oregon.

04:31The goal is to be able to alert populations in time and potentially save lives in the event of a major earthquake.

04:40A mega-earthquake of the type Chevauchement hit this region in 1964.

04:45Known as the Great Earthquake of Alaska, it reached a magnitude of 9.2 and lasted more than 4 minutes,

04:52thus becoming the most powerful earthquake recorded in the United States and North America.

04:57The tremors caused significant cracks and landslides.

05:02In Anchorage, many houses, infrastructure and roads were destroyed, because they were not designed to resist an earthquake of such intensity.

05:11In some areas, the landscape was definitively transformed.

05:15Thus, the coast near Kodiak and Hinchinbrook Island was elevated by 9 meters,

05:20while in towns such as Girdwood and Portage, the ground collapsed by 2.

05:25Roads had to be rebuilt at a higher height to prevent floods caused by the tides.

05:31A gigantic 8-meter tsunami destroyed the village of Chenega.

05:35Many coastal cities suffered significant damage, not only because of the earthquake, but also because of tsunamis and consecutive fires.

05:44The following months were marked by thousands of replicas of lower intensity.

05:50In August 2024, a moderate earthquake of magnitude 4.4 hit Los Angeles.

05:56Following this event, the Los Angeles Fire Protection Service inspected the city without reporting any major damage or injuries.

06:04However, in Pasadena, near the epicenter, a sewer burst inside the city hall, forcing the evacuation of the building.

06:12Fortunately, no tsunami risk was reported.

06:15The best way to reduce the risk of panic in these situations is to make an adequate preparation.

06:21Japan is among the regions of the world most exposed to earthquakes, due to its position at the intersection of four tectonic plates.

06:29Each year, about 1,500 earthquakes are powerful enough to be felt.

06:35This reality has led the Japanese to adapt their daily lives to these phenomena.

06:40Thus, a law adopted in 1950 requires that buildings be designed to resist shakings of a magnitude up to 7 without collapsing.

06:50An update, 30 years later, specified that buildings should only suffer minor damage during such an earthquake and continue to function normally.

06:59However, in the event of a more powerful earthquake, the regulation imposes that the priority is to avoid the collapse of the building in order to protect human lives.

07:09At a basic level, this involves reinforcing the structures with beams, pillars, and thicker walls to better resist shaking.

07:18Another approach is to install special cushions, made with materials such as rubber, at the base of the buildings.

07:25Some buildings even rest on large layers of mattresses that isolate them completely from the ground, which improves their protection against earthquakes.

07:33A skyscraper can oscillate significantly, with a displacement of up to 1.5 meters forward and backward.

07:40To limit damage, engineers also add devices called shock absorbers to each second floor up to the top of the building.

07:48These shock absorbers work like huge bicycle pumps, but filled with liquid rather than air.

07:54During quakes, the liquid resists compression and absorbs part of the energy generated by the quake.

08:02When they design skyscrapers, engineers strive to simplify and balance the structure as much as possible.

08:09This implies that each floor is a uniform height and that the support columns are distributed regularly.

08:16However, architects sometimes prefer more creative designs, which pushes them to look for compromise solutions to maintain both the aesthetics and safety of the building.

08:27For example, the Tokyo Skytree, one of the tallest towers in the world, associates a futuristic style with innovative devices designed to resist earthquakes.

08:37It integrates a central pillar, inspired by traditional Japanese pagodas, as well as seismic shock absorbers that dissipate the energy of the quakes, thus guaranteeing stability and safety.

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