When the Earth Quakes: Why and How?

Shock Waves

Solid does not necessarily mean rigid, as we can sense from a concrete parking deck bouncing under heavy traffic.

Comparably, we can sometimes see evidence on mountainsides and along road cuts that tremendous forces within the Earth’s crust have tilted and folded rock layers. And like broken concrete columns and floor slabs from buildings after earthquakes, rock layers also reveal their past stresses beyond breaking points. They contain what geologists call faults, which are fractures between displaced masses of rock. Because of pressures and jostling in the crustal mosaic of tectonic plates, the Earth is continuously vibrating from its endless quakes. Each one propagates a shock wave like ripples across a pond after its equilibrium is disturbed.

When Havoc Strikes

Natural forces controlling physical changes above and at the Earth’s surface display an immense range of energy levels between apparent tranquility and news-making catastrophes. For example, during the 15,000+ days between 1980-2022, the US National Atmospheric and Oceanic Administration recorded 341 extreme weather events costing at least $2.5 trillion. But by far the greatest loss of life and cost of damage result from occasional calamitous earthquakes (a thirteenth century word with ‘earth’ referring to the ground and ‘quake’ to trembling in fear).

Each step in the open-ended Richter Scale for earthquakes is massively more powerful in terms of dissipated energy than the next lower one. A US Geological Survey website explains that an 8.7 quake is about 23,000 times stronger than a 5.8 one, meaning that it would take about 23,000 quakes of magnitude 5.8 to equal the energy released by one magnitude 8.7 event. The US National Earthquake Information Center locates about 20,000 earthquakes around the globe each year. Based on more than a century of records, it expects these on average to include 15 in the magnitude 7 range and one greater than magnitude 8.

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At 5:36 pm in Anchorage, Alaska on Good Friday 1964 and lasting 4 minutes and 38 seconds, some five hundred years of accumulated stress along a 600-mile section of the convergent boundary between the Pacific and North American plates were unleashed with up to 60 feet of fault line movement. The result was a magnitude 9.2 mega-earthquake: the strongest in North American history and the second worst in world history. Costs of rebuilding devastated communities, mainly Anchorage, and port facilities up to 80 miles away became almost three trillion in today’s dollars.

The largest known earthquake occurred on the coast of Chile, south of Santiago, on May 22, 1960. With a cataclysmic 9.5 magnitude, and lasting over ten minutes, it triggered tsunamis across the Pacific Ocean that began at 80 feet high and were still 25 feet high 6,000 miles away in New Zealand. Here are three other severe examples from the last quarter century. Resulting from a 7.6 magnitude earthquake in Tangshan, China on July 28, 1976, a 7.0 magnitude earthquake in Haiti on January 12, 2010, and a 9.1 magnitude earthquake in Sumatra on December 26, 2004, with its tsunami striking 14 countries around the Indian Ocean, the unimaginable death tolls were 655,000, 315,000, and 228,000, respectively.

Turkey and northern Syria also have a history of severe earthquakes because they span a collision zone between the African, Anatolian, Arabian, and Eurasian crustal plates. The harrowing 50,000+ death toll from the recent spate of 7.8, 7.5, and 6.3 magnitude earthquakes exceeded the annual average recent death toll from all natural disasters worldwide. The severity was also evidenced by crumbling of the 2,200-year-old Gaziantep Castle, a UNESCO World Heritage Site. Incredibly, the section of the Earth’s crust abruptly displaced by the three main tremors and their aftershocks was 120 miles long and 15 miles wide.

The Big Picture

The greatest earthquake risks are along the boundaries of the ‘Pacific Rim of Fire,’ named for its most dangerous type of volcanoes. This is where ocean-floor crust is under-thrusting the edges of continents. Next is the broader zone over which the African, Arabian, and Indian plates are compressing the mountainous regions from the Alps to the Himalayas at the southern margin of the Eurasian Plate. The third distinct zone is the worldwide string of mostly mid-oceanic divergent and sideways plate boundaries with frequent low-magnitude quakes, such as Iceland and Hawaii (see last October’s and January’s blog posts). The Atlantic and Pacific Oceans are, respectively, widening and narrowing at rates of 1-4 inches per year (1,600 to 6,400 miles per 100 million years). 

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And the fourth area of risk comprises several scattered regions of continents, most notably the eastern interior of Africa and western interior of the US. Except where an old fault line harbors some lingering stress or where exploratory activity like ‘fracking’ for enhanced recovery of oil and gas resources disturbs an otherwise stable region, the majority of continental areas do not have earthquakes.

Public Education

As a geologist, I am concerned that this profession could and should do more to partner with school and lifelong educational systems, other science and engineering professions, the social sciences, and environmental humanities to acquaint society with summaries of natural hazard research. The contrast between Indigenous and non-Indigenous peoples in terms of a synergy with nature versus a failure to think and act sustainably has become glaring. Societies everywhere would wisely learn, for example, from the seven generation and good ancestor traditions of North American Iroquois and Dakota elders. Their communities are propelled by timeless values embracing both stability and needed adaptations.

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With California’s San Andreas Fault the world’s most famous fault line and with the Richter scale of earthquake magnitude an invention of California’s Charles Richter and Beno Gutenberg in 1935, it is unsurprising that a California nonprofit organization urges an uncustomary view of time. In 1996 the Long Now Foundation based in San Francisco observed that humanity was revving itself into “a pathologically short attention span”. It defined ‘now’ as yesterday, today and tomorrow; ‘nowadays’ as the last, present, and next decades; and ‘the long now’ spanning from 10,000 years ago to 10,000 years ahead.

Representing ourworldindata.org in 2022, natural disaster synthesists Hannah Ritchie, Pablo Rosado, and Max Roser stated: “Low-frequency, high-impact events such as earthquakes and tsunamis are not preventable, but such high losses of human life are. We know from historical data that the world has seen a significant reduction in disaster deaths through earlier prediction, more resilient infrastructure, emergency preparedness, and response systems. Those at low incomes are often the most vulnerable to disaster events: improving living standards, infrastructure, and response systems in these regions will be key to preventing deaths from natural disasters in the coming decades”.

The UN Office for Disaster Risk Reduction and International Science Council have both drawn attention to the fact that “five years after the UN launched a global monitor for disaster losses and prevention strategies, more than half of countries still do not have an adequate national disaster risk monitoring system”. For its part, the US Geological Survey estimated in 2015 that almost half of the American population is at risk of potentially damaging earthquakes. More alarming was that this survey nearly doubled its 2006 estimate of 75 million Americans in 39 states because population growth in at-risk areas outweighed the benefits of improving technologies.

Matters of Chance

Considering the scores of places on six continents where I have traveled, I have been fortunate to have only encountered three earthquakes.

• July 1, 1973: I had just finished fieldwork in the St. Elias Mountains of southwest Yukon and was at a basecamp at Mile 1054 on the Alaska Highway. During a phone call to verify flights back home, the trailer I was in violently rocked due, as soon would be known, to a 6.7 magnitude earthquake in neighboring southeast Alaska.
• June 25, 1995: I was in Taiwan for a cultural exchange. While touring the National Palace Museum in Taipei, its building suddenly shook and artifacts in display cases toppled. Visitors did not need evacuation orders. I soon learned that a 6.0 magnitude earthquake about 40 miles south had tilted several hillside apartment towers.
• August 23, 2011: While in the Baltimore Harbor tunnel along Interstate 95 to Washington, DC, a 5.8 magnitude earthquake occurred although this was not immediately known. Upon exiting the tunnel, just about every radio station was abuzz with news of evacuated buildings and the damaged tops of the Washington Monument and National Cathedral.

Ironically, the biggest natural disaster that I have experienced was Sandy, the largest Atlantic hurricane on record, which swept into the New Jersey / New York region on October 29, 2012, leaving a trail of damage that would cost $65 billion to repair. On January 30, 2015, days after the US Army Corps of Engineers released a post-Sandy report examining flood risks for 31,000 miles of the North Atlantic coast, President Obama issued a directive to federal, state, and local governments to adopt stricter siting and building standards because of climate change and sea-level rise projections. Since 2015 also, the UN’s Sendai Framework for Disaster Risk Reduction is a roadmap for how to make communities more resilient to the vagaries of nature.

Header image:
Anchorage, Alaska, 27 March
https://www.theatlantic.com/photo/2014/05/1964-alaskas-good-friday-earthquake/100746/