According to a detailed article published by The Los Angeles Times, in January of 2019, so many of today's cities are at critical risk from the massive increase of seismic activities, such as an earthquake.
It is believed, that year by year, the earthquakes in the biggest cities of America, like Los Angeles, San Francisco, and others, are becoming more and more sensitive to increased seismic activities. Many of them are growing stronger with each aftershock.
The article of Times is opened up with the Northbridge earthquake - which had happened 25 years ago. With the Northbridge disaster, alarming evidence started to grow, based on so many vulnerable types of buildings, that are at a high risk collapsing from a major shaking. This earthquake smashed hundreds of brittle concrete buildings, topped the number of apartments and tore apart hundreds of brick structures.
During this year, after the Northbridge disaster, some of the cities have taken the action of forcing building owners into acquiescences with the regulations and rules of earthquake protection. Yet, several other cities are still ignoring the threat.
New Rules and Regulations
Some of the cities, such as Los Angeles, have taken comprehensive action to ensure that the cities' buildings are retrofitted for the increase of earthquake protection and to be complemented with the new rules and regulations.
Requiting upwards of over 15.000 buildings for their seismic performance of improvements, the most extensive earthquake retrofit law was authored by Mayor Eric Garcetti, who was the instrumental of the following low. Since the low, San Francisco joined it and now this is mandating large swaths of the city's buildings for retrofitting and becoming docile with the new regulations and rules of seismic protection.
What Exactly Are Earthquakes?
Earthquakes can pose little danger directly to the people. As earthquakes are associated with shakings, you should know that people can not be shaken to death by an earthquake. In the movie scenes and in the fantastic books earthquakes are often described as the ground suddenly opening up and people falling into the giant pit. However, in real like it does not happen.
Effect Of Ground Shaking
The main earthquake hazard, which happens the first, is the effect of ground shaking. Buildings can be damaged due to this first main hazard, by the ground beneath them settling to another level than it could be before the earthquake or by shaking itself.
Buildings can also sink into the ground when it is saturated or substantially (more likely) soil strength and stiffness losses, that can be applied because of shakings during an earthquake.
When the soil and water are mixed, the ground becomes extremely soft and if the liquefaction occurs under buildings, they can start to lean, sink or tip over for several feet. After the earthquake is past and the water is settled back, the ground can firm up again. Liquefactions, in general, happen in the area where there are groundwater sources around.
Ground displacement is the second main earthquake hazard along with fault. When a building, a road or any structure, is built across a fault, the ground displacement can cause severe damage or even rip apart them.
The third main hazard is considered flooding. It occurs during an earthquake when the water from a reservoir or the river is the area for the epicenter. Earthquake during it can rupture or break levees or dams along rivers, damaging and even sweeping away people. A great deal of damage can also be caused by tsunamis or seiches.
The fourth main hazard of the earthquake is fire. Those fires can be started by broken power lines or gas lines, as well as by tipped over wood and coal stoves.
Most of the hazards people can be damaged with are coming from man-made structures and equipment themselves and from the shaking they receive from the earthquake. The real dangers to people are drowning in a flood caused by a broken dam or levee, being crushed in a collapsing building, getting buried under a landslide, and being burned in fires.
Types Of Seismic Waves
There are three types of seismic waves of earthquakes that are traveling across the crust of the Earth:
- First waves to arrive
- Also are called compression or sound waves
- Often are heard rather than felt
- Travel at 4–8 km/sec (14,000–28,000 km/h) in the earth’s crust
- Do not generally cause a lot of damage, except during the major earthquakes.
- Second waves to arrive
- Travel at 2.5–4 km/sec
- Pack the bigger punch because they are bigger and move at right angles to the direction of travel
- Their side-to-side motion is like a snake wriggling, and that is what causes the most damage to structures
- They can not travel through liquids because liquids have no shear strength.
- Travel around the surface layers of the earth.
- The slowest of the earthquake waves.
- They can travel around the whole earth from large earthquakes many times before they become too small to record on seismographs.
How Can Retrofitting Improve Seismic Performance?
Retrofits are comprehensive construction projects designed to assess a building’s current seismic performance. Structural integrity, foundation, and even torque are measured to determine the building's performance during an earthquake. Things like soft-story retrofits are for helping to ensure the soft-story buildings, which are something that cities like Los Angeles have thousands of. These types of retrofits strengthen the first story or the soft-story to ensure the improvement of the buildings' seismic performance dramatically. Meanwhile, the upper stories may still be considered vulnerable from an engineering standpoint, a soft-story retrofit is meant for strengthening the weakest link of the structures first. These retrofits can increase seismic performance and the earthquake protection of a building dramatically.
Army of Builders' in-house engineering team works directly with our team of builders to ensure that we retrofit upgrade any building, whether it be a home or a soft-story building so that it can remain safe from a devastating earthquake. We have another article about Earthquake Retrofit, once you want more details about this kind of retrofitting technique and strategies.
And in the city of Los Angeles, we are proud to lead the way to ensure that every building complies with the sweeping new rules and regulations designed to save lives at first, and also money and time.