Residents of this popular resort town experienced a rude awakening on September 3, 2024, when a magnitude 4.5 earthquake struck just before 5 a.m. The powerful tremor, later adjusted to 4.3 and a shallow depth of 5 kilometers (approximately 3 miles), was unprecedented for many locals, who reported a loud roar emanating from beneath the earth.
The event triggered an ongoing seismic swarm that has perplexed both the community and the scientific world. Cuauhtémoc Morgan, a well-known local journalist, delves into the origins of this phenomenon in his new book, "Secretos Bajo la Arena" (Secrets Beneath the Sand), now available on Amazon.
According to Morgan's analysis, the initial earthquake's shallow depth contributed to its intense impact. He highlights that the cause of the seismic activity was not immediately clear, even to experts. A special report by the National Seismological Service suggested the possibility of a previously unidentified fault line as the source of the initial quake, which then ignited the subsequent swarm.
Roberto Ortega, a geologist with the Center for Scientific Research and Higher Education of Ensenada (CICESE) based in La Paz, supports the theory of a new, uncharted fault, distinct from the historically known San José fault.
Alternative explanations from the Seismological Service include the possibility of underground land readjustment due to accumulated moisture from past cyclones and rainfall, leading to a landslide and the rupture of a fault.
Despite speculation on social media, Morgan emphasizes that scientific reports rule out a geothermal origin for the earthquakes, meaning there is no evidence of a nascent volcano beneath San José del Cabo.
What is particularly notable about this seismic event is the sheer number of aftershocks. In the first 30 minutes following the main tremor, 30 events ranging from magnitude 1.5 to 3.4 were recorded. Within the first two hours, an astonishing 200 aftershocks occurred, creating a continuous shaking sensation that continues to this day.
Morgan addresses and dismisses theories involving construction explosives or heavy machinery, asserting that the ongoing seismic activity is a unique geological event under intense scientific scrutiny.
Researcher Roberto Ortega had previously predicted the continuation of the seismic swarm for several months and the potential for more earthquakes exceeding magnitude 4.2, a prediction that has since been realized. He notes that earthquakes of this magnitude can be strong enough to topple walls.
In "Secretos Bajo la Arena," Cuauhtémoc Morgan aims to educate the public, particularly students, about the subsurface events. He points out that even low-magnitude earthquakes are strongly felt due to their shallow occurrence.
Morgan reminds readers that Baja California Sur has a history of significant seismic events, including a tsunami in Loreto in 1810 and a strong earthquake in La Paz in 1995. He underscores the importance of staying informed about earthquakes in the seismically active Los Cabos region.
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