On May 3, 1887, a powerful earthquake struck the southwestern United States, leaving a lasting impact on Arizona’s seismic history. With an estimated magnitude of 7.6, the 1887 Sonora earthquake remains the most significant seismic event ever recorded in Arizona.
Its epicenter was located along the Pitaycachi Fault in the San Bernardino Valley of Sonora, Mexico, approximately 40 miles south of Douglas, Arizona.
A Tremor Felt Across the Region
The earthquake’s effects were felt over an extensive area, with reports of shaking reaching as far north as Phoenix and as far south as Mexico City. In Arizona, the tremors were particularly intense in Cochise County, where eyewitnesses described ground fissures and liquefaction phenomena.
Buildings in towns like Tombstone experienced significant damage, though the sparsely populated nature of the region at the time meant that fatalities were limited. Overall, the earthquake resulted in approximately 51 deaths, primarily in northern Sonora, Mexico.
Geological Implications
The 1887 earthquake was a normal-fault event, characteristic of the extensional tectonic forces shaping the Basin and Range Province. Surface ruptures from the quake extended over 60 miles, with vertical displacements observed along the fault scarp.
This event marked the longest recorded normal-fault surface rupture in historic time in North America. The seismic activity highlighted the active tectonic processes occurring in the region and underscored the potential for significant earthquakes in Arizona.
Lasting Effects and Preparedness
In the aftermath of the 1887 earthquake, Arizona’s vulnerability to seismic activity became more apparent. While large earthquakes are infrequent in the state, the 1887 event served as a reminder of the potential risks.
Today, Arizona is home to over 100 known active faults, with the Northern Arizona Seismic Belt being the most seismically active region. Communities in areas such as Flagstaff and Yuma remain at risk, not only from local faults but also from distant seismic events originating in neighboring states and Mexico.
In response to these risks, initiatives like the “Great Arizona ShakeOut” have been established to promote earthquake preparedness. These drills encourage residents to practice safety measures such as “Drop, Cover, and Hold On” to reduce injuries during seismic events. Additionally, the Arizona Geological Survey continues to monitor seismic activity and provide resources to help communities understand and mitigate earthquake hazards.
Conclusion
The 1887 Sonora earthquake stands as a testament to the seismic potential of the southwestern United States. Its widespread effects and the extensive surface ruptures it caused serve as a reminder of the dynamic geological forces at play beneath Arizona’s surface. While the state may not experience frequent large earthquakes, the 1887 event underscores the importance of preparedness and awareness in mitigating the impacts of future seismic activity.