An earthquake is a sudden shaking of the ground, caused by the rapid release of energy within the Earth’s lithosphere that generates seismic waves. This energy release occurs due to the movement of Earth’s crust along geological faults. Earthquakes vary widely in intensity and are quantified by magnitude.
Understanding Earthquake Magnitude
Earthquake magnitude is a scientific measure of the energy released at the earthquake’s source. Initially, the Richter scale was widely used to measure earthquake magnitude, primarily by assessing the amplitude of seismic waves recorded on a seismograph. While the Richter scale remains a commonly referenced term, particularly for smaller to medium-sized quakes, the Moment Magnitude Scale (MMS) has become the standard for measuring all earthquake sizes. The MMS provides a more accurate assessment by considering factors such as the area of the fault rupture and the amount of slip that occurred. It is important to distinguish that magnitude reflects the earthquake’s inherent size, not the intensity of shaking felt at a particular location, which can vary based on distance and local geology.
Experiencing a 3.5 Earthquake
A 3.5 magnitude earthquake is considered minor, with typically subtle effects. People located near the epicenter might experience a slight tremor, a gentle bump, or a brief swaying sensation. It is common for objects indoors to rattle or for hanging items to swing gently. Damage to structures is highly unlikely, and significant structural damage usually does not occur until magnitudes reach above 4 or 5. Injuries are rare, and such events typically do not disrupt daily life.
The Bigger Picture: Comparing Earthquake Magnitudes
A 3.5 magnitude earthquake is a frequent, minor seismic event. Earthquakes between magnitudes 3.0 and 3.9 are classified as “minor” and are often felt but rarely cause damage. Globally, approximately 130,000 earthquakes in this magnitude range occur annually. In contrast, “moderate” earthquakes typically range from 5.0 to 5.9, while “major” earthquakes are those with magnitudes between 7.0 and 7.9. Large, damaging earthquakes are far less common, with only about 16 major earthquakes occurring worldwide each year.
Responding to Minor Earthquakes
For a minor earthquake, the recommended safety procedure is “Drop, Cover, and Hold On.” This involves dropping to your hands and knees, taking cover under a sturdy piece of furniture like a table or desk, and holding on until the shaking stops. If no sturdy cover is available, getting down near an interior wall and covering your head and neck with your arms provides some protection. For those outdoors, move to an open area away from buildings, trees, streetlights, and power lines, then crouch until the shaking subsides. Practicing these actions helps build muscle memory for larger, potentially more dangerous events.