The Science Behind the Shake
At their core, earthquakes are primarily caused by the rupture of geological faults, which are fractures in the Earth’s crust where blocks of rock move past each other. This movement is driven by the continuous motion of tectonic plates. There are three main types of faults: normal, reverse (or thrust), and strike-slip. While all can cause earthquakes, reverse faults, particularly those along convergent boundaries, are associated with the most powerful events, known as megathrust earthquakes, which can exceed magnitude 8.0. Beyond tectonic shifts, earthquakes can also be triggered by volcanic activity, landslides, and even human activities such as mining, fracking, and nuclear weapons testing, a phenomenon known as induced seismicity. The point of initial rupture deep within the Earth is called the hypocenter or focus, with the epicenter being the point directly above it on the ground surface. Source
The energy released by an earthquake is measured on seismic magnitude scales, with the Moment Magnitude Scale (Mw) being the standard for its accuracy in reflecting the actual energy released. A key characteristic of this scale is that each unit increase in magnitude represents approximately a thirty-fold increase in the energy released. For instance, a magnitude 8.6 earthquake releases energy equivalent to 10,000 atomic bombs of the size used in World War II. This energy propagates through the Earth as seismic waves: faster P-waves (longitudinal), slower S-waves (transverse), and surface waves (Rayleigh and Love waves), with the latter two typically causing the most damage. Source
Global Seismicity and Recent Activity
The Earth experiences an estimated 500,000 earthquakes annually that are detectable by modern instrumentation, with about 100,000 of these being felt by people. Historically, the United States Geological Survey (USGS) estimates an average of 18 major earthquakes (magnitude 7.0-7.9) and one great earthquake (magnitude 8.0 or greater) occur each year, a rate that has remained relatively stable since 1900. The vast majority of the world’s earthquakes, approximately 90%, occur within the 40,000-kilometer-long horseshoe-shaped zone known as the Pacific Ring of Fire. Source
Recent seismic activity highlights the Earth’s continuous motion. In the past 24 hours alone, there have been 94 earthquakes of magnitude 1.5 or greater globally, with 773 in the past 7 days, and 3,672 over the last 30 days. The largest earthquake this year, as of July 2025, was a magnitude 7.7 event near Sagaing, Myanmar. Other significant recent quakes include a magnitude 6.7 earthquake west-southwest of Tual, Indonesia, on July 14, 2025, and a magnitude 6.2 event near Punta de Burica, Panama, on the same day. Additionally, a magnitude 5.7 earthquake struck northwest of San Vicente Pacaya, Guatemala, on July 8, 2025, and a magnitude 6.3 was recorded west-southwest of Riverton, New Zealand, on July 7, 2025. The Euro-Mediterranean Seismological Centre (EMSC) also reported a magnitude 6.2 earthquake in Western Turkiye on April 23, 2025. Source, Source
Impacts and Consequences
The effects of earthquakes extend far beyond the initial ground shaking. Primary impacts include ground rupture, where the Earth’s surface visibly breaks and displaces along the fault line, and soil liquefaction, where water-saturated granular material temporarily loses strength and behaves like a liquid, causing structures to tilt or sink. Secondary hazards are equally devastating, encompassing landslides, fires (often due to damaged gas or electrical lines), and tsunamis, particularly when large offshore earthquakes displace the seabed. Flooding can also occur if dams are damaged or rivers are blocked by earthquake-induced landslides. The human toll includes injuries, loss of life, and extensive damage to critical infrastructure such as roads, bridges, and utility networks, leading to long-term recovery challenges. As the saying goes, “Earthquakes don’t kill people, buildings do,” underscoring the importance of resilient infrastructure. Source, Source
Mitigation and Preparedness
While precise earthquake prediction (specifying time, location, and magnitude) remains elusive despite significant research, earthquake forecasting, which provides probabilistic assessments of hazards over years or decades, is an active area of study. Early warning systems, like ShakeAlert, can provide crucial seconds of notice before ground shaking begins, allowing for immediate safety actions. Preparedness is paramount. This involves earthquake engineering to design and retrofit structures to withstand shaking, and comprehensive emergency management strategies. Individuals are advised to practice “Drop, Cover, and Hold On” during an earthquake, secure heavy household items, develop a family emergency communications plan with an out-of-state contact, and assemble a supply kit. After an earthquake, it’s vital to expect aftershocks, move away from damaged buildings, and stay informed through reliable news sources. Source, Source
As our understanding of seismic activity grows, so does our capacity to mitigate its risks. Continuous monitoring by organizations like the USGS and EMSC, coupled with public education and preparedness initiatives, are vital steps in navigating the inherent challenges of living on an active Earth.
