Volcano Monitoring: Volcanic Tremors or Distant Earthquake? Distinguishing Seismic Signals

Hawaii is one of the most seismically active areas in the world, producing thousands of earthquakes each year. It also produces a signal called a tremor, which can originate from a volcanic system.

An earthquake is characterized by the appearance of slow seismic waves that may last for minutes or several days when there are ongoing volcanic eruptions. It is important to identify an earthquake because this signal may be associated with fluid movement, which can sometimes indicate an increased chance of an eruption. However, it is often difficult to pinpoint the location of an earthquake because the waves appear slowly from the background noise and may last for minutes, weeks, or even years – a shallow earthquake at Kilauea or Mauna Loa is often directly associated with ongoing volcanic activity.

In contrast, earthquakes are usually sharp at their onset and are easy to see. The time at which the earthquake signal appears at several stations that make up the USGS Hawaiian Volcano Observatory (HVO) seismic network can be used to pinpoint the location of the earthquake. Alternatively, the location of tremor explosions is often estimated by looking at the signal size (or seismic amplitude) at multiple seismic stations and then determining the approximate location and depth.

For example, a shallow earthquake that occurs at the summit of Mauna Loa may have strong seismic amplitude at stations near the summit of Mauna Loa, but the signals are very weak by the time the signal reaches seismic stations at Kilauea. In contrast, an earthquake that occurs deep in Pahala may have roughly the same seismic amplitude at several stations near Pahala, but then become weak at seismic stations in Kona or Hilo.

It is important to note that not all earthquake-like signals are associated with volcanic activity, and in some cases may not originate in Hawaii. A 7.4 magnitude undersea earthquake off Chile at 3:50 p.m. Hawaii time on July 19 caused strong ground shaking in Chile, as recorded by the HVO seismic monitoring network.

The earthquake also generated a powerful hydroacoustic signal (a sound wave that travels through water) – called a T phase – that was recorded throughout the Pacific Ocean basin. T phases are very different from a tsunami and are not dangerous to people. They travel at about 1.5 kilometers per second (about 3,355 miles per hour) and therefore take less than two hours to travel from Chile to Hawaii.

In this case the wave travels across the ocean primarily within a horizontal layer called a stabilization and acoustic measurement channel (SOFAR), which tends to trap or guide hydroacoustic waves efficiently. When the T-phase reaches the coast of Hawaii, its energy is converted back into a seismic signal that looks remarkably like local volcanic tremors on the HVO seismic network.

Because the Hawaiian Seismological Observatory closely monitors seismic signals, HA scientists often need to distinguish between local volcanic tremors and the T phase of a distant earthquake. The figure here shows an example of a deep local tremor detonating beneath Pahala at 4:13 p.m. Hawaiian Standard Time on July 30. Comparing this local tremor detonation to the previous T phase event from Chile on July 19, we see that the T phase event has time-separated arrivals across the HA network—a result of the slow speed of sound waves in water. In contrast, the deep volcanic tremors beneath Pahala arrive at different HA stations at approximately the same time—a result of the local source and the faster wave speeds found in basaltic rocks.

Scientists at the Hawaiian Seismological Observatory can distinguish between local earthquakes and distant earthquakes by evaluating the arrival times of the signals and their amplitude. They can also confirm that the observed signal is a T phase by searching for large events in the global earthquake catalog. This seismic search is one of many aspects of Hawaiian volcano monitoring.

Volcano activity updates

Kilauea has not yet erupted. Its USGS alert level is “advisory.”

Seismic activity and ground deformation continue at the summit of Kilauea and the upper to middle rift zone, with another event near Pauahi Crater on August 19-20. Over the past week, approximately 800 earthquakes were recorded below the eastern upper rift zone of Kilauea and approximately 100 events were recorded between Maunaolo and Pu'u'u'u in the central portion of the eastern rift zone within Hawai'i Volcanoes National Park. Over the past week, the summit of Kilauea and the eastern central rift zone have shown slow expansion, followed by slow contraction during the intrusive event. Since then, relatively little ground deformation has been recorded in these areas. Unrest may continue to wax and wane with changes in magma input to these areas; changes can occur rapidly, as can the potential for eruption.

Mauna Loa has not erupted yet, and the USGS volcanic alert level is at normal.

Fourteen earthquakes have been reported in the Hawaiian Islands over the past week; Here is a list of earthquakes that only had a magnitude of 3: a 4.7 magnitude earthquake 15 km (9 miles) south of Fern Forest at a depth of 6 km (4 miles) on August 22 at 12:52 a.m. Hawaiian Standard Time, a 3.4 magnitude earthquake 6 km (3 miles) south of Volcano at a depth of 0 km (0 miles) on August 20 at 9:22 a.m. Hawaiian Standard Time, a 3.2 magnitude earthquake 8 km (4 miles) south of Volcano at a depth of 0 km (0 miles) on August 20 at 7:22 a.m. Hawaiian Standard Time, a 3.8 magnitude earthquake 11 km (6 miles) NE of Pahala at a depth of 31 km (19 miles) on August 20 at 5:32 a.m. Hawaiian Standard Time, and a 3.9 magnitude earthquake 30 km (18 miles) W-NW of Hawaiian Ocean View at a depth of 11 km (7 miles) on August 20 at 3:52 a.m. Hawaiian Standard Time, and a 3.2 magnitude earthquake 6 km (3 mi) south of the volcano at a depth of 1 km (0 mi) on August 20 at 2:46 a.m. Hawaiian Standard Time.

The Croatian Military Council continues to closely monitor Kilauea and Mauna Loa.

Please visit the HVO website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano images, maps, recent earthquake information, and more. You can email questions to [email protected].

Volcano Watch is a weekly article and activity update written by scientists and representatives of the U.S. Geological Survey's Hawaiian Volcano Observatory.

What Are The Main Benefits Of Comparing Car Insurance Quotes Online

LOS ANGELES, CA / ACCESSWIRE / June 24, 2020, / Compare-autoinsurance.Org has launched a new blog post that presents the main benefits of comparing multiple car insurance quotes. For more info and free online quotes, please visit https://compare-autoinsurance.Org/the-advantages-of-comparing-prices-with-car-insurance-quotes-online/ The modern society has numerous technological advantages. One important advantage is the speed at which information is sent and received. With the help of the internet, the shopping habits of many persons have drastically changed. The car insurance industry hasn't remained untouched by these changes. On the internet, drivers can compare insurance prices and find out which sellers have the best offers. View photos The advantages of comparing online car insurance quotes are the following: Online quotes can be obtained from anywhere and at any time. Unlike physical insurance agencies, websites don't have a specific schedule and they are available at any time. Drivers that have busy working schedules, can compare quotes from anywhere and at any time, even at midnight. Multiple choices. Almost all insurance providers, no matter if they are well-known brands or just local insurers, have an online presence. Online quotes will allow policyholders the chance to discover multiple insurance companies and check their prices. Drivers are no longer required to get quotes from just a few known insurance companies. Also, local and regional insurers can provide lower insurance rates for the same services. Accurate insurance estimates. Online quotes can only be accurate if the customers provide accurate and real info about their car models and driving history. Lying about past driving incidents can make the price estimates to be lower, but when dealing with an insurance company lying to them is useless. Usually, insurance companies will do research about a potential customer before granting him coverage. Online quotes can be sorted easily. Although drivers are recommended to not choose a policy just based on its price, drivers can easily sort quotes by insurance price. Using brokerage websites will allow drivers to get quotes from multiple insurers, thus making the comparison faster and easier. For additional info, money-saving tips, and free car insurance quotes, visit https://compare-autoinsurance.Org/ Compare-autoinsurance.Org is an online provider of life, home, health, and auto insurance quotes. This website is unique because it does not simply stick to one kind of insurance provider, but brings the clients the best deals from many different online insurance carriers. In this way, clients have access to offers from multiple carriers all in one place: this website. On this site, customers have access to quotes for insurance plans from various agencies, such as local or nationwide agencies, brand names insurance companies, etc. "Online quotes can easily help drivers obtain better car insurance deals. All they have to do is to complete an online form with accurate and real info, then compare prices", said Russell Rabichev, Marketing Director of Internet Marketing Company. CONTACT: Company Name: Internet Marketing CompanyPerson for contact Name: Gurgu CPhone Number: (818) 359-3898Email: [email protected]: https://compare-autoinsurance.Org/ SOURCE: Compare-autoinsurance.Org View source version on accesswire.Com:https://www.Accesswire.Com/595055/What-Are-The-Main-Benefits-Of-Comparing-Car-Insurance-Quotes-Online View photos