Seismologist available to explain recent earthquakes

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Seismologist available to explain recent earthquakes

Expert can discuss whether the events are connected, what to expect next

Following a series of powerful earthquakes that struck Japan, the United States and Venezuela yesterday, Northwestern University seismologist Suzan van der Lee is available to explain what triggered this unusual burst of seismic activity, whether the distant events are connected and what people should know about forthcoming aftershocks.

Van der Lee is the Sarah Rebecca Roland Professor of Earth and Planetary Sciences at Northwestern's Weinberg College of Arts and Sciences. In her research, she applies data science to millions of records of seismic waves in order to decode seismic signals, which harbor valuable information about the Earth's interior dynamics.

Van der Lee is available at [email protected] or by contacting Amanda Morris at [email protected].

A brief Q&A with van der Lee follows:

Three earthquakes occurred yesterday - two in Venezuela, one in Japan and one in the United States. Is it common for earthquakes to cluster in time?

The magnitudes of these earthquakes are 7.2 and 7.5 in Venezuela, 6.9 for the one near Kuji, Japan, and 5.6 for the one near Redwood Valley in California.

Around the world, there are about 15 earthquakes annually with a magnitude of 7 or higher, 150 with a magnitude of 6 or higher and 1,500 with a magnitude of 5 or higher. The U.S. alone experiences approximately one earthquake with a magnitude of 5 or higher every single week. Most of these are in Alaska. California annually experiences about two earthquakes with a magnitude of 5 or higher. Yesterday's earthquake near Redwood Valley was one of those.

It is not common for two earthquakes with magnitudes of 7 or higher to occur in the same day, but it can happen occasionally. Over the past 30 days, there have been two days (June 8 and June 16) when two earthquakes with a magnitude of higher than 6 but lower than 7 occurred. Even when two earthquakes with magnitudes of 7 or higher happen on the same day, it is even less common for those two earthquakes to happen so close to each other in space and time as the two Venezuelan earthquakes, which occurred within 1 minute and 5 kilometers from one another. The last such pair of earthquakes occurred on the East Anatolian Fault in Turkey, near the border with Syria, in February 2023. Before that, such a pair occurred near Ridgecrest, California, in 2019.

Is there any way these recent global events are connected?

Each of these four earthquakes occurred on a boundary between two tectonic plates. All plates move in a different direction compared to surrounding plates, so the plate edges impose resistance (friction) on the neighboring plate's movement. When the plates eventually overcome the friction, it's manifested as an earthquake. So, in some global tectonic way, all earthquakes are connected to the dynamics of tectonic plates and the dynamics of the Earth's hot, compressed interior.

However, the two earthquakes in Venezuela are more directly connected and occurred independently from the earthquakes in Japan and California. All earthquakes need to happen to help the plates move. But exactly when and where they occurred is somewhat random. No one can predict when and where earthquakes occur with sufficient practical precision.

Were the two Venezuelan earthquakes separate events or an earthquake plus a foreshock or aftershock?

These earthquakes occurred close in space and time, a phenomenon usually observed for foreshocks and aftershocks. However, foreshocks and aftershocks typically have magnitudes that are much smaller (at least one magnitude point) than the main shock. Because the two magnitudes of these two large earthquakes are close to one another, this pair of nearby earthquakes is called a doublet. That implies that they are related, for example, by occurring on the same fault or fault system, with similar slip directions, where the second earthquake might have been helped by small, local stress changes caused by the first earthquake. That said, the dominant cause of the two earthquakes is tectonic stress that has built up over many years due to the South American and Caribbean tectonic plates moving past one another in opposite directions - slowly but steadily.

Any ideas of what we'll see over the next couple days? Can people in affected regions expect a series of aftershocks?

Yes, aftershocks will continue for many days. They typically have smaller magnitudes, but already damaged buildings can still sustain more damage from lesser shaking from the aftershocks that follow the main shock.

Suzan Van Der Lee

Professor of Earth and Planetary Sciences

• [email protected]