Semantics of the Salton Sea: When does a swarm become a chain?

When the ground along the Salton Sea started shaking on June 5 and didn’t stop, scientists thought it was another swarm. But was it?

Written by Debbie Kelp, Ph.D., Scripps Institution of Oceanography, University of California, San Diego (Kinect_with_Sci), Ph.D. Winyuan Fan, Scripps Institution of Oceanography, University of California, San Diego, and Gabe Lasky, Ph.D. The Scripps Institution of Oceanography, University of California, San Diego

Citation: Kilb, D., Fan, W., Laske, G., 2021, Semantics at the Salton Sea: When Does a Swarm Become a Serial?, Temblor, http://doi.org/10.32858/temblor.181

On June 5th at 1 a.m. local time, a series of small to moderate earthquakes began to shake the southeastern shore of the Salton Sea in Southern California. The largest event to date was a 5.3-magnitude earthquake about 11 hours after the series began. Over the past few days, more than 1,000 earthquakes have occurred in this area.

At first glance, this looked like a fairly ordinary earthquake swarm – a common occurrence in the Salton Sea region. However, when diving deeper into the earthquake data, the recent earthquake series may actually be a series of major tremors/aftershocks. What that means for residents of this shaky region doesn’t change: the chance of an earthquake exceeding a magnitude 7 the following month is still less than 1% (see USGS aftershock forecast). For researchers, these events offer a new perspective on the source of the physics of these earthquakes.

Earthquakes vs swarms

If you look at a map of the world’s earthquakes, it’s not as random as the paint spots in a Jackson Pollock painting. Instead, earthquakes tend to occur in patterns along the edges of tectonic plates. When you zoom in for a closer look, you begin to see rather mysterious earthquake patterns, with many events participating in space/time clusters as part of earthquake swarms or major tremor/aftershock sequences. An earthquake swarm is a series of earthquakes that do not have a single obvious main shock, and subsequent earthquakes in the sequence may migrate geographically over time. The main shock/aftershock sequence includes a large earthquake followed by many smaller earthquake aftershocks.

We think of the main shock/aftershock sequence as following a well-defined causal relationship: the largest aftershocks are usually about a unit of magnitude smaller than the main shock (Kilb & Vernon, 2020), and it is possible to predict how long the aftershock sequence may last and what size aftershocks Expected earthquake (Michael et al., 2020). In a typical aftershock sequence, the magnitude and number of events follows an exponential decrease – Omori’s law. On the other hand, swarms do not behave well. Sometimes it contains many earthquakes of medium size. Sometimes swarms consist of only small earthquakes. Swarm periods are variable and can span days, weeks, or even years (Ross et al., 2020). This complexity makes earthquake swarms difficult to predict but also fascinating to study.

The mechanisms that cause acute earthquakes are thought to be different from those that cause tectonic earthquakes. The latter is caused by changes in forces, or stresses, that eventually cause the movement of tectonic plates. One of the main driving mechanisms for swarms is underground fluid migration. When fluids spread through fault systems, they can lead to earthquakes of similar size. Swarms have also been associated with hydraulic fracturing (i.e., hydraulic fracturing) and often occur in geothermal regions (Hill et al., 1975; Ellsworth, 2013).

Squadrons of the Salton Sea

Swarms are a common occurrence near the Salton Sea in Southern California, where they have been observed for more than two decades (Fig. 1).

Figure 1. Map of the Salton Sea region of Southern California. Earthquakes (magnitude 2.0 or greater) over the past two decades are depicted as earthquakes in gray and earthquakes presumably part of the swarms are color-coded: 2000 olives; 2005 orange; 2012 green; 2016 yellow, 2020 red, and 2021 blue (three days of data only).

Some Salton Sea swarms are more robust than others in terms of their temporal evolution, spatial footprint and earthquake magnitudes. For example, the rates of seismic activity in the 2000 and 2016 swarms were rather weak, but the current swarm (if it is) is characterized by a high rate of seismic activity (see Table 1 and Figure 2). There is no one-size-fits-all aspect to swarms even when limited to one location.

Table 1. Comparison of the Salton Marine Squadrons. These values ​​are subjective and swarm periods were determined from a qualitative examination of the temporal evolution of the series. Data up to June 8, 2021. Fig. 2. Comparison of time evolution of earthquakes of magnitude 2.5+ within each Salton Sea Swarm data set (lists the overall y-axis; color coding as in Fig. 1). The temporal behavior of the first 2.5 days of these sequences shows some similarities, with bursts of seismicity followed by silence, which is a typical sign of earthquake swarms.

It is located south of the Salton Sea in a complex tectonic region. The San Andreas Fault to the east marks the transformation boundary along which the Pacific Plate slides northward after the North American Plate. To the south, the deflection of the plates causes the Gulf of California to widen. The geometry of the drag stresses is complex, resulting in many long and short faults, some parallel to the San Andreas, others perpendicular to it. An earthquake at one fault may increase stress on another fault, resulting in an earthquake in the adjacent fault.

Geothermal production sites are located within the Salton Sea region, which can affect how fluids are transported within the fault system, often resulting in fluid transport. Given this, many researchers have assumed that fluids migrating across land are the primary driving mechanisms for swarms in the southern Salton Sea region, although these have not caused major earthquakes here yet. However, it is possible that a combination of fluid migration and movement of tectonic plates can cause earthquakes, in which case a set of events can look like a swarm and succession of major/follower shocks.

We suggest that the 2021 squadron (as well as the previous squadron in 2012) is not a swarm at all and is instead akin to a series of major shocks/aftershocks (referred to as the ‘sequence’ henceforth). Our first evidence that this may be true is that seismic decay rates appear more like a sequence, fundamentally different from the decay behavior of a typical swarm (Fig. 3).

Figure 3. Comparison of temporal magnitude distributions for the 2005 and 2021 data sets and the 2016 Anza main/aftershock sequence. To us, the behavior of the 2021 data looks more similar to the 2016 sequence, showing the scarcity of events beyond magnitude 3. This is different from the behavior of 2005 which has many earthquakes of ~3 magnitude, which is more common for an earthquake swarm. spatial patterns

The spatial patterns of these data sets show different generalized spatial fingerprints for different years. The 2000, 2005, 2016 and 2020 swarms mapped areas of earthquakes along a single fault heading from northeast to southwest, perpendicular to the San Andreas fault. Data for 2012 and 2021 differ, and instead identified two defects from different directions (Fig. 4). This is intriguing and requires an explanation. These observations are consistent with our conjecture that the 2012 and 2021 swarms were in fact sequences, not swarms, or at least some kind of hybrid swarm/sequence.

Figure 4. Map showing approximately 1,000 earthquakes recorded by Caltech/USGS seismic networks during the first two days of the 2021 Salton Sea event. This map includes smaller earthquakes than we presented in Table 1 above (thresholds of magnitude 1.3 and 2.5 , Straight). The largest earthquake of magnitude 5.3 is shown as an open blue circle. Focal mechanisms are determined using the instantaneous tensor algorithm. Credit: Egill Hauksson, Caltech Future Research

Collectively, the two decades of data from the Salton C earthquake only provide a blurred view of earthquake patterns, too vague to explore the intricacies within the fault system. More research is also needed to better distinguish between swarm and sequence and to understand how a set of mechanisms makes a chain of events adopt some of the features of both swarm and sequence. The necessary next step is to optimize the site for all these events. Often this move from an initially ambiguous set of events leads to multiple specific errors from different directions and depths.

In other parts of Southern California, it has been suggested that faulty interconnection could explain the spatial divisions between swarms (Ross et al., 2020). For example, some fault patches may experience more total slippage than others and are therefore more damaged and permeable, allowing fluids to move more easily within these damaged areas. It will eventually be interesting to reveal the interrelationships between the Salton Sea faults and how they interact with each other across different spatio-temporal scales.

What does this mean?

Do these Salton Sea earthquake swarms/sequences indicate that the Great San Andreas earthquake rupture will occur soon? To answer this question, scientists use past observations to predict what might happen in the future. Here, we have presented the results of six swarms or sequences near the Salton Sea that occurred over a period of ~20 years. These data show no evidence that swarms or sequences lead to major earthquakes in the San Andreas Fault. But in all honesty, we have very few observations to make any far-reaching future claims, just as a survey of six people on a topic does not correctly represent what residents might think.

The message we take home here is that we live in an earthquake country. We need to be prepared and have a protection and response plan in place. Building codes protect our structures, and regular earthquake drills heighten our awareness. Be prepared, don’t be afraid.

references

Ellsworth, W.L. (2013). Injection induced earthquakes. Science, 341.

Hill, D. P., Mowinckel, P. & Peake, L. G. (1975). Earthquakes, active faults and geothermal zones in Imperial Valley, California. Science, 188, 1306-1308.

Kilb, D. and Vernon, F. (2020), Southern California hit by moderate but severe earthquake, Temblor, http://doi.org/10.32858/temblor.084.

Michael, A. J., McBride, S. K., Hardebeck, J. L., Barall, M., Martinez, E., Page, M. T., van der Elst, N., Field, E. H., Milner, KR & Wein, A. M. (2020). Statistical Seismology and Communications for the USGS Operational Aftershock Forecast on the November 30, 2018 AD 7.1 Anchorage, Alaska, earthquake. Earthquake Research Letters, 91, 153-173.

Ross, ZE, Cochran, ES, Trugman, DT & Smith, JD (2020). The 3D fault structure controls the dynamics of earthquake swarms. Science, 368, 1357-1361.

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