Milestone: The Tangshan Earthquake

A. Name the specific impact/hazard you are investigating. State the specific city/town you will be focusing on for the Milestone!

The hazard being investigated is the Tangshan earthquake with a magnitude of 7.6 that hit the city of Tangshan in China in 1976, causing massive destruction of the industrial city and death of over 200,000 people.

B. Describe how the impact/hazard formed in scientific terms.

The earthquakes was formed when plate tectonics collided and slid against each other thus causing friction and vibrations making rocks to break along fault lines. Plate tectonics are believed to be floating on molten rock of the earth’s mantle and move very slowly towards or away from each other.

C. Describe the location of the hazard and add a map that illustrates the information.

The Tangshan earthquake occurred in Tangshan city in Northern China, Northeast of Hebei province. Tangshan is majorly a coal mining and industrial city.

Figure 1: Map showing Tangshan City in Hebei Province (Bao et al., 2018).

D. Describe the population of the location (city/town) that was impacted (demographic makeup).

Tangshan city has a population of 7, 536, 000 people with a population density 560/km2

and GDP of ¥605.383 billion. The main religion in Tangshan city is Buddhism.

E. Include data in graphic form that indicates the past frequency of the hazard type you chose for the geographic area that surrounds your specific event

Figure 2: A line graph showing the past frequency of earthquake in the Tangshan region.

Section 2:

Identify Earth cycles and systems influencing your impact/hazard and BRIEFLY describe these.

a) Earth cycles

i. Water- Underground water can cause changes in pore pressure in rocks through freeze and thaw thus inducing earthquakes.

ii. Rock- Softer rocks experience stronger effects of earthquakes compared to hard rocks since softer rocks easily break. Therefore, areas that lie on softer rocks are likely to experience more damage as a result of earthquakes than those that sit on harder rocks.

iii. Plate tectonics- The plate tectonics are in constant movement and as a result, they meet and slide against each other, an effect that causes friction and shaking, and causing rocks to break along the fault lines thus resulting in earthquakes.

b) Earth Systems

i. Biosphere-The biosphere is the earth’s sphere where all living creatures exist. During an earthquake, the biosphere can experience landslides, liquefaction and tsunamis thus magnifying the effect of earthquakes.

ii. Hydrosphere- The hydrosphere is the liquid water component of the earth. An earthquake may cause a sudden vertical shift of the ocean floor where tectonic plates meet resulting in a tsunami thus magnifying earthquake destruction.

iii. Human impact-Human impact on the earth’s surface like mining and blasting which causes vibrations can cause earthquakes. Further, activities like fracking, deep water and CO2 injection have also been shown to increase the frequency of earthquakes.

Section 3:

Describe whether the influencing factors identified in section 2 (cycles & systems) have been consistent over time or are changing.

The earth cycles such as water, rocks and plate tectonics are relatively constant. Plate tectonics, for instance, move at a constant rate of one to two inches per year.  However, human impact has increased over the years. Currently, mining activities have become more frequent, and activities like blasting are often done (McGarr et al., 2015). Further, injecting water and CO2 deep into the earth during oil mining has increased. Fracking technology is also frequently used to mine oil and natural gas.

Section 4:

As a result of any potential change in the cycles and systems you identified do you believe the risk of a repeat event is greater or less than in the past?

As a result of the increased human activities, the risk of earthquakes is greater currently compared to the past. Injection of water has been shown to increase pressure and fracture rocks besides also lubricating the fault lines all which result in increased risk of earthquakes (Bao et al., 2018). Additionally, building dams increase pressure on the earth’s surface which increases the chances of an earthquake. Nuclear blasting has increased over the years which creates fault lines thus increasing the risk of earthquakes in recent times.

References

Bao, F., Li, Z., Yuen, D. A., Zhao, J., Ren, J., Tian, B., & Meng, Q. (2018). Shallow structure of the Tangshan fault zone unveiled by dense seismic array and horizontal-to-vertical spectral ratio method. Physics of the Earth and Planetary Interiors, 281, 46-54.

McGarr, A., Bekins, B., Burkardt, N., Dewey, J., Earle, P., Ellsworth, W. & Rubinstein, J. (2015). Coping with earthquakes induced by fluid injection. Science, 347(6224), 830-831.