Earthquake Early Warning Systems

Earthquake early warning (EEW) systems alert users when potentially damaging shaking is expected at their location. ShakeAlert® (fig. 1) (https://www.shakealert.org) is the USGS-managed EEW system for the West Coast of the United States. Imminent shaking alerts are automatically delivered through emergency communications systems, including push notifications to mobile devices. The seconds to tens of seconds of warning can allow people and automated systems to take actions to protect life and property from destructive shaking. These seconds to tens of seconds of warning represent the most advanced form of earthquake early warning.

National Volcano Early Warning System

The National Volcano Early Warning System (NVEWS) is a national-scale plan to ensure that volcanoes are monitored at levels equal to their threats. Threat ranking incorporates the hazards posed by each volcano and the potential exposure of people, property, and infrastructure. The USGS categorizes potentially active U.S. volcanoes as Very High, High, Moderate, Low, and Very Low threat. Currently, many of the 161 potentially active volcanoes in the United States have insufficient monitoring systems, while others have obsolete equipment. The goal of NVEWS is to ensure that the most hazardous volcanoes are properly monitored with a variety of modern instruments (fig. 2) well before the onset of activity, making timely and accurate hazard forecasts possible minutes, days or even weeks before an eruption.

In addition, NVEWS seeks to advance several capabilities of the U.S. volcanology community through:

Similarities and Differences

NVEWS involves increasing the number and types of monitoring instruments—including seismometers and global positioning system (GPS) receivers like those used for EEW—for the Nation’s highest threat volcanoes. However, seismometer locations and early warning time frames are distinctly different for EEW and NVEWS. The two systems have different missions and technical requirements and will be operated independently. At select EEW sites, broadband seismometers and webcams can be added to provide NVEWS function. Volcano monitoring networks also include other types of ground-based sensors, which typically are not part of regional seismometer networks supporting EEW (fig. 2). Table 1 summarizes the many differences between EEW and NVEWS.

While the two warning systems address different hazards that occur on different time scales, the data from seismic instruments in both systems may be similar and will be shared in real-time. They will assist the entire nation in addressing natural hazards, whether from earthquakes, volcanoes, or secondary hazards (for example, tsunamis or ground failure). This is especially important in areas of the country, such as California, the Pacific Northwest, and Alaska, where large damaging and tsunami-generating earthquakes can occur in proximity to active volcanic systems.

Seismic instruments deployed independently for NVEWS and EEW will help detect both tsunami-generating earthquakes and volcanic eruptions; real-time data from these instruments will be shared with Hawaii and Alaska's National Oceanic and Atmospheric Administration tsunami warning centers. In many remote areas, such as the Aleutian Islands, American Samoa, and the Commonwealth of the Northern Mariana Islands, the first indication of a large tsunamigenic earthquake or volcanic eruption may come from Global Seismic Network seismometers or those deployed as part of NVEWS on remote islands. Despite their distance from population centers and significant infrastructure, where much of EEW is focused, these seismometers are necessary because of potential threats posed by remote volcanoes to remote populations, civil and military aviation, and maritime vessels.

Opportunities for VHP-EHP Collaboration

At each volcano, the VHP already leverages existing seismic and geodetic instrumentation maintained by the EHP, universities, States, and private organizations. During times of unrest, especially at under-monitored or low-threat volcanoes, these networks will be extremely important for hazard assessment until the regional networks are improved by a VHP response.

Volcano monitoring networks with multiple instrument types also help the USGS better identify whether earthquake swarms are being caused by volcanic activity. Ambiguity in the cause of an earthquake swarm can arise when a swarm is near a volcano or within a distributed volcanic field. To determine the ultimate origin and significance of increased seismicity, VHP and EHP scientists and their partners analyze seismic and other types of data from ground-based instruments (for example, pressure sensors, tiltmeters, GPS, gas emission, and web cameras) and data from satellites (such as, radar and gas emission).

In all instances, digital communications networks can be leveraged between EHP and VHP, as they already are in the Pacific Northwest, California, and Alaska. The two programs are in frequent communication, share some staff expertise and logistics, and take advantage of joint software and hardware development and equipment purchase contracts (for example, digital broadband seismometers and batteries bought in large orders as a cost-saving measure). Both programs are always looking for opportunities to leverage instrumentation and communication networks in a cost-effective manner to maximize the Nation’s resilience to earthquake and volcano hazards.