Mexico was struck by a powerful earthquake Tuesday—the second in two weeks.

Mexico Hit With Two Powerful Earthquakes In Two Weeks

Earlier this month, a quake with a magnitude of 8.1, Mexico’s strongest in a century, was felt as far as Mexico City and Guatemala City. The tremor, which left at least 61 dead, was said to have been felt by 50 million people across the country.

Tuesday’s quake reached a 7.1 magnitude, collapsing buildings, cracking highways, and killing hundreds.

According to Behzad Fatahi, associate professor of geotechnical and earthquake engineering at the University of Technology Sydney, both earthquakes were caused by the rupture of fault lines in the North American tectonic plate. “When fault lines rupture,” Fatahi explained, “they can induce further ruptures as a chain effect in other parts of the same fault or nearby fault lines.”

Mexico’s President Enrique Peña Nieto Declares National Emergency

In his address following the quake, President Enrique Peña Nieto told Mexican citizens, “We are facing a new national emergency.”

The earthquake left Mexico’s capital city in chaos, with thousands of people fleeing into the streets and dozens trapped under debris and collapsed buildings. Many stayed to assist in the rescue effort, with civilians working alongside soldiers and rescuers.

Luis Felipe Puente, head of the national Civil Defense agency, confirmed Wednesday that the death total had risen to 226.

Tuesday’s Earthquake Wasn’t An Aftershock

While aftershocks can happen any time up to months after the main quake strikes, Fatahi says that Tuesday’s earthquake is not an aftershock of the massive one two weeks ago. This latest quake will probably be followed by aftershocks in the weeks ahead. Fatahi explains, however, that the likelihood of powerful earthquakes in this area has now been “reduced”:

However, since two major earthquakes of magnitude 7 and above have occurred in a matter of 10 days in the region toward southern part of North American tectonic plate, significant stored energy has been released from the ground, which means that the likelihood of much larger earthquakes in the region has reduced now. 

Tuesday’s earthquake struck on the anniversary of another deadly quake that hit Mexico in 1985 and killed nearly 10,000.