Tuesday, 13 June 2017

Natural Disasters and Family Misfortunes 4: Earthquakes

Among natural disasters, earthquakes rate right up top as the deadliest. Each year thousands of people are killed or left homeless. Whole families, and by extension family lines have been lost during these events. Current and historical records document the effects and aftermaths of these major intrusions of Mother Nature in the lives of humans.

Since the Earth is in a dynamic state, changes to its surface through such processes as land shifts will continue to happen and any communities or infrastructure, not to mention people it the way will in all likelihood be harmed.

The 1906 earthquake in the San Francisco area, mentioned briefly in my blog post of 18 April 2017, was felt along the entire north coast of California, particularly devastating the urban area of San Francisco where it destroyed 80% of the city. Over 3,000 people died as a result of the quake and its resultant fires.

Major earthquakes are concentrated along the edges of the Earth’s crustal plates where relative movements cause the plates to impinge on each other. California is a region where the North American and Pacific plates slide laterally in opposite directions, grinding against each other and creating major fractures and fault zones. Movement is frequent and never-ending, in a geological sense, resulting in severe tremors and vertical movement.
World map showing major crustal tectonic plates – source United States Geological Survey 
Along coastal areas tsunamis may form as a result of the shifting of the seabed, adding a secondary potential for destruction. These large ocean waves can travel thousands of miles across open water, eventually appearing along distant shorelines with highly destructive force.

There is an informative website that lists earthquakes by period, country and region and also compares the devastation in terms of magnitude, cost of damage and numbers of deaths. These are primarily events that occurred during more recent times and documented in the published literature. There is no doubt similar events occurred in the past centuries before mass media. One major difference is in the perceived human toll. The rapid and large increase in population of the past 150 years has led to more people and communities being caught up in the destruction with many more deaths and greater destruction of infrastructure.

Ancient writings, along with archaeological and geological studies demonstrate the occurrence of destructive earthquakes going back thousands of years many of which affected early communities. Turkey and Syria, for example, lie at the junction of three crustal plates – African, Arabian and Eurasian (Anatolian sub-plate). The region has been the site of numerable major earthquakes and volcanic eruptions over millions of years. Records dating back a thousand years describe the destruction from these events. Earthquakes centered near the Greco-Roman city of Antioch, in AD 115 and AD 526 each apparently resulted in the deaths of hundreds of thousands of people. The deadliest earthquake in recorded history occurred in Shaanxi, China in AD 1556 when over 830,000 people were killed.

Besides the well-documented 1906 San Francisco event, there have been many major earthquakes in North America including one in AD 1700 in Cascadia (Washington State & British Columbia). No written records exist from the time period in North America describing the earthquake, however, in Japan there are reports of a tsunami thought to have originated along the North American coast. Tree ring evidence from the Pacific Northwest also show a major disruption in forest growth from flooding of low-lying areas. The earthquake is believed to have been caused by the North American plate slipping over the Juan de Fuca plate with a major shift along the deep subduction zone.
Structure of the Cascadia region and history of major earthquakes – source United States Geological Survey

While earthquakes by themselves may not have been the primary reasons for the migration of people, they certainly have been the cause of the deaths of thousands and the early demise of family lines. Family historians may wish to look at natural disasters such as earthquakes when studying the reasons why ancestors died or moved. Such natural phenomena are often part of the stories about families.

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