Volcano Watch — Summer 2017 goes out like a lion with hurricanes and earthquakes: reminders to be prepared for Nature's fury

On September 8, as Irma, the second of four hurricanes to sweep across the Atlantic 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 September 19, a M7.1 earthquake struck roughly 80 km (50 mi) southeast of Mexico City. While not as strong as the September 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 a M8.0 earthquake struck along Mexico's western coast in 1985. Though centered hundreds of miles from Mexico City, the 1985 earthquake is often referred to as the "Mexico City earthquake" because of its devastating effects on 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 September 19, 2017, earthquake, as well.

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 that 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 over days, earthquakes occur relatively instantaneously. Yet, if we know that an earthquake has 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 have credited Mexico's system with helping to reduce casualties associated with the September 2017 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 has struck can help minimize losses, it is critically important that we are prepared and know what to do to reduce damage and injury when earthquakes, like the 2006 Kīholo and Māhukona events, occur in Hawaii. Across 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 actually strikes. Because September 19 marks the anniversary of the 1985 earthquake, Mexico City had 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 Hawai‘i ShakeOut at 10:19 a.m. HST on Thursday, October 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 Update

This past week, Kīlauea 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 lavaentering the ocean near Kamokuna and surface breakouts downslope of Pu‘u ‘Ō‘ō. 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 over 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 Hawai‘i during the past week.