As the summer months began to wind down this year, nature’s fury began to wind up and grab much of the news cycle.
On Sept. 8, as Irma, the second of four hurricanes to sweep across the Atlantic Ocean and Gulf of Mexico regions thus far in 2017, was approaching Cuba, a magnitude-8.1 (M8.1) earthquake struck the western coast of Mexico. This was the largest earthquake to strike Mexico in 100 years. It caused widespread damage, injured hundreds and took dozens of lives.
Less than two weeks later, on Sept. 19, an M7.1 earthquake struck roughly 80 km (50 mi) southeast of Mexico City. While not as strong as the Sept. 8 earthquake, this second event resulted in far greater damage, killing hundreds and injuring thousands of people, principally because of its proximity to Mexico’s capital and metropolitan area, where roughly 20 million people live.
Coincidentally, this M7.1 earthquake struck 32 years to the day since an M8.0 earthquake struck along Mexico’s western coast in 1985. Though centered hundreds of miles from Mexico City, the 1985 earthquake often is referred to as the “Mexico City earthquake” because of its devastating effects to that city.
Thousands perished in the 1985 Mexico City earthquake. Seismic waves were amplified by the lake bed and river sediments beneath the city. Strong ground shaking caused many buildings to collapse, trapping their occupants beneath and within. These same effects came into play during the Sept. 19, 2017, earthquake.
An important consequence of the 1985 Mexico City earthquake was the development and implementation of upgraded building codes in Mexico. These upgraded codes made it less likely newly constructed buildings would collapse during an earthquake, and they possibly prevented even greater destruction and casualties resulting from last month’s earthquake.
Unlike hurricanes, which can be observed and tracked as they develop through a period of days, earthquakes occur relatively instantaneously. Yet, if we know an earthquake occurred, and it is possibly large enough, we can estimate how soon damaging seismic waves will begin to shake different areas based on how far they are from the earthquake’s epicenter.
After the 1985 earthquake, Mexico was one of the first countries to use this principle to provide early warning of imminent strong earthquake shaking. Some reports credited Mexico’s system with helping reduce casualties associated with last month’s earthquakes. The United States Geological Survey is coordinating a U.S. West Coast earthquake early warning effort with university and other partners in California, Oregon and Washington state.
While being warned that a damaging earthquake struck can help minimize losses, it is critically important we are prepared and know what to do to reduce damage and injury when earthquakes, such as the 2006 Kiholo and Mahukona events, occur in Hawaii. Throughout the U.S., annual Great ShakeOut earthquake awareness drills (https:www.shakeout.org/Hawaii) emphasize “Drop! Cover! and Hold On!” until strong shaking stops to avoid being struck by falling objects and before evacuating a damaged structure.
Practicing what to do during a large earthquake will help us take appropriate actions when the next one strikes. Because Sept. 19 marks the anniversary of the 1985 earthquake, Mexico City conducted an earthquake drill earlier that day, just a matter of hours before the M7.1 earthquake struck. Along with preparation and planning, the importance of developing, implementing and enforcing appropriate building codes cannot be overstated.
As we drop, cover and hold on during this year’s Great Hawaii ShakeOut at 10:19 a.m. Thursday (Oct. 19), let’s also dedicate a quiet moment to those adversely impacted by recent earthquakes. And let’s think about ways we can improve our personal and community preparedness and resiliency to extreme natural events.
Volcano activity updates
This past week, Kilauea Volcano’s summit lava lake level fluctuated with summit inflation and deflation, ranging about 32-39 m (105-128 ft) below the vent rim. On the East Rift Zone, the 61g flow remained active, with lava entering the ocean near Kamokuna and surface breakouts downslope of Pu‘u ‘O‘o. The 61g flows do not pose an immediate threat to nearby communities.
Mauna Loa is not erupting. Rates of deformation and seismicity did not change significantly during the past week, but persist above long-term background levels. Small-magnitude earthquakes occurred beneath the summit caldera and upper Southwest Rift Zone, primarily at depths less than 5 km (3 mi), with some deeper events at depths of 5-13 km (3-8 mi). GPS measurements continue to show deformation related to inflation of a magma reservoir beneath the summit and upper Southwest Rift Zone. No significant changes in volcanic gas emissions were measured.
No earthquakes were reported felt on the Island of Hawaii during the past week.
Visit the HVO website (https://volcanoes.usgs.gov/hvo) for past Volcano Watch articles, volcano updates and photos, recent earthquake info, and more. Call for summary updates at 808-967-8862 (Kilauea) or 808-967-8866 (Mauna Loa). Email questions to askHVO@usgs.gov.
Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and colleagues.
