Language
Country/Area
No result found
The Secret of Epicenter Distance and Earthquake Wave Intensity: From Mexico City to Your Home!
The amplification effect of seismic waves is closely related to the geological structure beneath the ground. This phenomenon will cause strong vibrations in shallow geology. We witnessed the widespread damage caused by this phenomenon during the 1985 Mexico City earthquake. By studying local earthquake effects, we can better assess the impact of strong earthquakes and their potential risks. This article aims to provide insights into the definition of this phenomenon, the case of the 1985 Mexico City earthquake, and the results of earthquake studies in other cities, such as Caracas.
"The enhancement effect of seismic waves can lead to a strong amplification of ground shaking under unfavorable geological conditions, such as the presence of sediments."
Definition of phenomenon
As seismic waves propagate, they reflect and refract between different geological layers. When seismic waves encounter different geological structures, they cause changes in energy, especially at the interface between soil and rock. This seismic wave amplification effect is called the "seismic site effect." When the surface geological layers (such as river sediments) are softer, the amplitude of the shaking is greater, thus intensifying the impact of the earthquake.
Specifically, when a shear wave (SH wave) reaches such an interface, it causes the generation of reflected and refracted waves. Studies have shown that when the strata change greatly, this reflection and refraction will significantly affect the amplitude and frequency of seismic waves, thereby intensifying the shaking on the ground.
Case Study: 1985 Mexico City Earthquake
The 1985 Mexico City earthquake is a classic example of the power of seismic site effects. The epicenter of the earthquake was located on the Pacific coast, hundreds of kilometers from Mexico City, but the shaking was extremely strong and caused huge damage. Data from different measuring stations show that the closer the location is to the epicenter, the higher the amplitude of the vibration measured.
"At the Campos station, which is closest to the epicenter, the maximum acceleration recorded was 150 cm/s², while the Teacalco station, 200 km from the epicenter, recorded only 18 cm/s²."
This change in vibration amplitude mainly comes from the attenuation of seismic waves during propagation, or the energy loss caused by seismic waves in different materials. Especially in shallow sediment foundations like Mexico City, the non-rigid nature of the seismic weight further amplifies its fluctuations. The sediment layer in Mexico City is 40 meters thick. When shear waves of the same frequency arrive, it causes a resonance effect, thereby amplifying the vibration effect.
Theoretical Analysis of Earthquake Site Effects: Horizontal Stratification
Further theoretical analysis shows that in the case of horizontal layers, we can describe the reflection and refraction behavior of shock waves through simple wave equations. This analysis helps us understand the behavior of seismic waves as they bounce back through different geological layers and derive a formula for calculating amplitude ratios from the data.
"At certain frequencies, the amplification effect of seismic waves can reach significant levels, which is crucial for predicting the earthquake resistance of buildings."
Seismic site effects in sedimentary basins: the case of Caracas
In the Caracas sedimentary basin, earthquake site effects are stronger, especially at the basin edges, which can amplify the shaking by five to ten times. The study shows that this amplification effect is closely related to the geometry of the basin and the characteristics of its geological layers.
By running digital models, the researchers were able to simulate how vibrations would be amplified in the Caracas metropolitan area at different frequencies. The data shows that at certain frequencies, the amplification of shock waves is incredibly strong, which not only affects the design of buildings but also poses a threat to the lives of people living in these areas.
ConclusionThe intensity of seismic waves and the impact of an earthquake on a city can vary significantly depending on the characteristics of the geological formations. The Mexico City case is a reminder that strong shock waves can lead to dire consequences in urban settings, especially in areas with poor geological conditions. Using these analysis results, we can better predict future earthquake risks and take appropriate preventive measures.
When faced with unknown natural disasters, are you ready to protect yourself and those around you?
