Venezuela hit by deadly twin earthquakes: The fascinating science behind how we detect and measure massive tremors

Wednesday night saw a devastating series of quakes hit Venezuela as a magnitude 7.2 earthquake was swiftly followed less than 60 seconds later by an even larger magnitude 7.5 quake, leaving in its wake at least 32 dead, over 700 injured, and destroying crucial municipal infrastructure across Venezuela's north-central coast. The first tremor struck at a depth of 22 kilometers from the coastal city of Morón, located in the province of Yaracuy, around 160 kilometers west of Caracas, whereas the second shallow tremor registered at a depth of 10 kilometers. The two-part assault knocked out Venezuela's main international airport, stopped functioning subway systems, cut gas lines, and even created shockwaves in places as far as Bogotá, Colombia, and the Brazilian Amazon. The acting President of Venezuela, Delcy Rodríguez, stated that the current death toll did not include victims in the disaster region of La Guaira state, as according to USGS estimates, final casualty numbers may reach into the thousands. The USGS reported the first tremor to be of magnitude 7.1 before upgrading it to 7.2 just hours after; the quick revision of such parameters demonstrates just how difficult it is to track and evaluate such data. Earthquakes occur as a result of the movements of tectonic plates in the Earth's outer crust. When two rocky blocks violently slip past each other via a crack line, or a fault, decades' worth of stored stress is suddenly released as kinetic energy. The quakes from Wednesday occurred on a strike-slip fault system along the coast of Venezuela, which means that the tectonic blocks slid past each other horizontally. This friction produces a burst of energy in the form of seismic waves. To capture this energy, international observatory networks use an extremely sensitive apparatus called a seismograph. A modern seismograph instrument includes a detector, or a seismometer, which consists of a heavy pendulum, or mass, hanging on a high-tension spring. The body of the instrument is directly attached to solid bedrock. During an earthquake, the ground, bedrock, and instrument frame move together. However, because of the law of inertia, the weighty suspended mass is resistant to moving and therefore stays almost immobile. The recorder writes down the physical difference between the immobile mass and vibrating frame in the form of zigzagging wave lines called seismograms. While one single seismograph can detect nearby earthquakes, finding the epicenter requires the use of a widespread regional network. Earthquakes radiate two main types of underground waves: P-Waves (Primary Waves): compressional waves that move the fastest. S-Waves (Secondary Waves): shear waves, which shake the ground perpendicularly. Measuring the exact time difference between the arrival of the fast P-waves and slow S-waves at a particular observation point, the scientists calculate the exact distance the tremor traveled. With the help of the repetitive computer procedure, data collected at three or more distinct observation points are correlated in order to locate the exact place, depth, and origin of the earthquake. Global tracking networks: Nations susceptible to the effects of tectonics possess networks of hundreds of stations like this one. For example, the National Center for Seismology (NCS) of India uses a network of 172 seismic stations stretching from Ladakh to the Andaman Islands; among them is the Mumbai station which has been monitoring seismograms without interruption since 1899. Over the last hundred years, many technological advances have been made to interpret seismograph wiggles as precise numbers. Richter Scale (Local Magnitude—M L) Developed in 1935 by Charles Richter to classify local earthquakes in California, the scale uses logarithmic values based on the amplitude of the largest wiggle observed on a seismograph. Each step on the scale is ten times greater than the preceding one. But the Richter scale is saturated during huge global events because it cannot reliably differentiate between a big earthquake and an absolute disaster. Moreover, it was structurally constructed for California's geology, thus requiring frequent modifications. Moment Magnitude Scale (MW) The Moment Magnitude Scale, invented in 1979 by seismologists Thomas Hanks and Hiroo Kanamori, is now used as a standard by all modern organisations like the USGS. Whereas the richter measures a solitary wiggle on a graph, MW assesses the total physical energy output of the actual fault line. Three specific measurements go into this calculation: As a consequence of assessing the total physics of the fault line, the moment magnitude scale is unsaturated and thus more accurate for mega-earthquakes than the Richter scale. However, this system necessitates complex mathematical modeling of the entire waveform, which is why preliminary field readings tend to be revised in the hours following any large event. For thousands of years, human cultures explained the trembling of the Earth through the action of mythological underground monsters—from giant catfish in Japan to monstrous spiders and serpents elsewhere. One of the earliest natural explanations came in the form of the philosopher Aristotle, who speculated that trapped underground winds produced the vibrations. One of the earliest known devices designed for detecting tremors was created in 132 AD by the Chinese scientist Zhang Heng. The scientist invented a bronze jar with eight dragon heads pointing outwards; each had a bronze ball held right above the mouth of the toad. In case of an earthquake, the displacement of an internal pendulum would trigger the release of a ball in the direction of the shaking. The breakthrough towards modern seismic science came after the disastrous Lisbon earthquake and tsunami of 1755, claiming more than 70,000 lives and leading European scientists to record all observations systematically. British professors John Milne, James Ewing, and Thomas Gray, who taught at the Imperial College in Tokyo managed to invent the first highly sensitive seismographs in the 1880s. A little later, American geologist Grove Karl Gilbert discovered that tremors originate due to faults, while researcher Harry Fielding Reid developed a concept of the "elastic rebound theory," proving that geological pressure accumulates gradually throughout decades until it breaks suddenly. Statistics: Major tremors worldwide Earthquakes vary greatly by their intensity; however, disasters like the one experienced in Venezuela on Wednesday do not happen often. Earthquake classification magnitude range, and average annual occurrence globally The records maintained by the USGS indicate that in the year 2010, the maximum number of major earthquakes was reported to be 23. As per records, the largest instrumental earthquake in the history of man is the Great Chilean Earthquake, which occurred in the year 1960 and had an intensity of magnitude 9.5. Venezuela lies at a very active point between the South American plate and the Caribbean plate. Although minor earthquakes can be frequent in nature in such zones, double-strike earthquakes are not very common. The earthquake that occurred on Wednesday can be compared in intensity with that of the earthquake that took place in 1967, killing around 236 people, or with that which occurred in the year 1812, taking away about 30,000 lives. Stay informed on all the latest news, real-time breaking news updates, and follow all the important headlines in india news and world news on Zee News.