earthquake overview
Beijing time on February 6, 2018, a magnitude 6.5 earthquake occurred in the waters near Hualien County, Taiwan, with a depth of 11 kilometers. The earthquake caused the collapse of building structures such as Hualien Tongshuai Hotel, Yunmen Cuidi Building, No. 2 Guosheng Sixth Street, No. 41 Guosheng Sixth Street and Qixingtan Bridge. Among them, the second-floor B&B and the second-floor B&B in Yunmen Cuidi Building was the most serious. It is analyzed that the intensity of the earthquake reached the highest earthquake intensity of Taiwan 7 degrees (equivalent to 8-9 degrees of earthquake intensity in mainland China).
According to the latest media reports on the evening of the 9th, the number of victims killed in the Hualien earthquake has risen to 17, including 9 mainland tourists, and another 278 people have been injured.
Disaster Analysis 1
Some experts pointed out that the common points of the four collapsed buildings in Hualien are: are all soft-footed buildings . Soft-footed buildings are also called weak-story buildings at the bottom. The common point of this type of building is that to meet the special functional needs of the building or to facilitate use, the bottom one to two floors are designed as a larger space, the columns are taller and there are fewer filling walls. For example, the bottom floor is used as a hall, parking lot, shop, etc. The upper floor uses more filling walls as separations, as a residence, etc. In addition, more arcades are built on the bottom floor of buildings like Taiwan, and arcades have one wall less than other floors. In addition, the first floor is for the store, and the columns are raised high, and forms a soft foot phenomenon with a head heavy and light feet, hard on the top and soft on the bottom. If the direction of the soft foot is exactly the same as the direction of the seismic wave , and some accidental factors in structural design and construction, it is easy to have an unfortunate event of a collapse of the bottom layer.
Disaster Analysis 2
The location of the faults that collapsed during this earthquake and caused the earthquake, from As can be seen in the figure below, the collapsed structures are distributed near the fault . According to data, there are 33 active faults in Taiwan, which are divided into two categories according to their activity degree. 20 are the most active first type of active faults, including the Milun fault, etc.
NARlabs distribution of collapsed buildings in the report
Depth analysis
Hualian station earthquake records Here is a bit different from the common seismic waves we have. Taking the Wenchuan seismic wave as an example, it can be seen from the figure that due to the large magnitude of Wenchuan earthquake, the fault has two ruptures, and the duration of the strong seismic wave is close to 2 minutes. The duration of the strong seismic wave recorded by the Hualien station is much shorter, only about 10 seconds. However, between 25 seconds and 30 seconds, there are two "conspicuous" ”. This large wave is called "pulse".
If the acceleration is replaced with velocity and displacement, the "big wave" will be more obvious. The peak value of the east-west velocity pulse is 118.1cm/s, the peak value of the displacement pulse is 71.0cm, the velocity pulse of north-south earthquake is 80.4cm/s, and the peak value of the displacement pulse is 71.5cm.
According to research, this "big wave" may have more complex effects on buildings, and even significantly aggravate the damage of buildings.
Comparison of earthquake records in Hualien Station and 8-degree fortification earthquake input
analysis found that in the small and medium-sized period period (0-0.4s), the difference between the two is not big, while in the medium-long period period (0.4-6s), ht The average value of ml2 Hualien earthquake is significantly higher than the design value. The design curve specified in seismic design specification is the statistical average. If the site where the structure is located is special and is very close to the fault, the earthquake intensity will greatly exceed the average value, which will often cause serious earthquake disasters.
Disaster Warning
Earthquake causes huge disasters to mankind, and also leave us extremely profound lessons and inspiration. Destructively After the earthquake, the buildings located in the living fault of and its nearby buildings were destroyed. People truly realized the terrifying power of the living fault at the cost of blood and tears. Live faults are considered to be "untimed bombs" buried underground in cities and villages. Disaster investigation warns us that all buildings that attach importance to earthquake resistance and meet the requirements of earthquake resistance may not be damaged, or the damage is obviously lighter.
Note: Some pictures are from the Internet
