Archive for the ‘Earthquake’ Category
A fault system that runs from San Diego to Los Angeles is capable of producing up to magnitude 7.4 earthquakesWednesday, March 8th, 2017
Scripps : Scripps Institution of Oceanography at the University of California San Diego.
The study, “Seismic constraints on the architecture of the Newport-Inglewood/Rose Canyon fault: Implications for the length and magnitude of future earthquake ruptures,” appears in the American Geophysical Union’s Journal of Geophysical Research.
Within the central and eastern United States, the number of earthquakes has increased dramatically over the past few years. Between the years 1973–2008, there was an average of 21 earthquakes of magnitude three and larger in the central and eastern United States. This rate jumped to an average of 99 M3+ earthquakes per year in 2009–2013, and the rate continues to rise. In 2014, alone, there were 659 M3 and larger earthquakes. Most of these earthquakes are in the magnitude 3–4 range, large enough to have been felt by many people, yet small enough to rarely cause damage. There were reports of damage from some of the larger events, including the M5.6 Prague, Oklahoma earthquake and the M5.3 Trinidad, Colorado earthquake.
This increase in earthquakes prompts two important questions:
- Are they natural, or man-made?
- What should be done in the future as we address the causes and consequences of these events to reduce associated risks?
Increasing Rate of Earthquakes Beginning in 2009
The earthquake risk for Oklahoma and southern Kansas is expected to remain significant in 2017, threatening 3 million people with seismic events that can produce damaging tremors.Thursday, March 2nd, 2017
The 2016 forecast indicated high seismic hazard (greater than 1% probability of potentially damaging ground shaking in one year) in five focus areas: Oklahoma–Kansas, the Raton basin (Colorado/New Mexico border), north Texas, north Arkansas, and the New Madrid Seismic Zone. During 2016, several damaging induced earthquakes occurred in Oklahoma within the highest hazard region of the 2016 forecast; all of the 21 moment magnitude (M) ≥4 and 3 M≥5 earthquakes occurred within the highest hazard area in the 2016 forecast. Outside the Oklahoma–Kansas focus area, two earthquakes with M≥4 occurred near Trinidad, Colorado (in the Raton basin focus area), but no earthquakes with M≥2.7 were observed in the north Texas or north Arkansas focus areas. Several observations of damaging ground‐shaking levels were also recorded in the highest hazard region of Oklahoma.
The 2017 forecasted seismic rates are lower in regions of induced activity due to lower rates of earthquakes in 2016 compared with 2015, which may be related to decreased wastewater injection caused by regulatory actions or by a decrease in unconventional oil and gas production.
Nevertheless, the 2017 forecasted hazard is still significantly elevated in Oklahoma compared to the hazard calculated from seismicity before 2009.
New USGS maps identify potential ground-shaking hazards in 2017 from both human-induced and natural earthquakes in the central and eastern U.S.
New USGS maps identify potential ground-shaking hazards in 2017 from both human-induced and natural earthquakes in the central and eastern U.S., known as the CEUS. This is the second consecutive year both types of hazards are forecasted, as previous USGS maps only identified hazards from natural earthquakes. This research was published today in Seismological Research Letters.
Approximately 3.5 million people live and work in areas of the CEUS with significant potential for damaging shaking from induced seismicity in 2017. The majority of this population is in Oklahoma and southern Kansas.
Research also shows that an additional half million people in the CEUS face a significant chance of damage from natural earthquakes in 2017, which brings the total number of people at high risk from both natural and human-induced earthquakes to about 4 million.
“The good news is that the overall seismic hazard for this year is lower than in the 2016 forecast, but despite this decrease, there is still a significant likelihood for damaging ground shaking in the CEUS in the year ahead,” said Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project.
The 2017 forecast decreased compared to last year because fewer felt earthquakes occurred in 2016 than in 2015. This may be due to a decrease in wastewater injection resulting from regulatory actions and/or from a decrease in oil and gas production due to lower prices.
Despite the decrease in the overall number of earthquakes in 2016, Oklahoma experienced the largest earthquake ever recorded in the state as well as the greatest number of large earthquakes compared to any prior year. Furthermore, the chance of damage from induced earthquakes will continue to fluctuate depending on policy and industry decisions, Petersen noted.
“The forecast for induced and natural earthquakes in 2017 is hundreds of times higher than before induced seismicity rates rapidly increased around 2008,” said Petersen. “Millions still face a significant chance of experiencing damaging earthquakes, and this could increase or decrease with industry practices, which are difficult to anticipate.”
Important Note: In the west, USGS scientists have focused on the hazard from natural earthquakes. Induced earthquakes have been observed in California as well, but they don’t significantly change the regional hazard level, which is already high due to frequent natural earthquakes.
What are Induced Earthquakes?
Induced earthquakes are triggered by human activities, with wastewater disposal being the primary cause in many areas of the CEUS. Wastewater from oil and gas operations can be disposed of by injecting it into deep underground wells. Injected fluids cause pressure changes that can weaken a fault and therefore bring it closer to failure. Most injection wells do not trigger felt earthquakes, suggesting that a combination of many factors contribute to such events.
“By understanding the relationship between earthquakes and wastewater injection, informed decisions can be made on processes such as controlling the volumes and rates of wastewater injected and determining which wells are most susceptible to inducing earthquakes,” said Petersen.
States with High Hazard
The maps indicate an especially high ground-shaking hazard in five areas of the CEUS in 2017. These same areas were identified in the 2016 forecast.
Induced seismicity poses the highest hazard in two areas, which are Oklahoma/southern Kansas and the Colorado/New Mexico area known as the Raton Basin. In those areas, there is a significant chance that damaging levels of ground motion will occur in 2017.
Enhanced hazard from induced seismicity was also found in Texas and north Arkansas, but the levels are significantly lower in these regions than that forecasted for 2016. While earthquakes are still a concern, scientists did not observe significant activity in the past year, so the forecasted hazard is lower in 2017.
There is also a high hazard for natural earthquakes in the New Madrid Seismic Zone. The NMSZ is the only one of the five identified areas that has not experienced induced earthquake activity. The NMSZ had a higher rate of natural earthquakes in the past three years, leading to a slightly higher hazard potential compared to previous years in portions of Arkansas, Missouri, Illinois, Kentucky and Tennessee.
“The 2016 forecast was quite accurate in assessing hazardous areas, especially in Oklahoma,” said Petersen. “Significant damage was experienced in Oklahoma during the past year as was forecasted in the 2016 model. However, the significantly decreased number of earthquakes in north Texas and Arkansas was not expected, and this was likely due to a decline in injection activity.”
“There is specific concern in parts of the central U.S. since the forecasted hazard levels are higher than what is considered in current building codes, which only incorporate natural earthquakes,” said Petersen.
People living in areas of higher earthquake hazard should learn how to be prepared for earthquakes. Guidance can be found through FEMA’s Ready Campaign.
Spotlight on Oklahoma
Between 1980 and 2000, Oklahoma averaged about two earthquakes greater than or equal to magnitude 2.7 per year. However, this number jumped to about 2,500 in 2014, 4,000 in 2015 and 2,500 in 2016. The decline in 2016 may be due in part to injection restrictions implemented by the state officials. Of the earthquakes last year, 21 were greater than magnitude 4.0 and three were greater than magnitude 5.0.
USGS research considers a magnitude 2.7 earthquake to be the level at which ground shaking can be felt. An earthquake of magnitude 4.0 or greater can cause minor or more significant damage.
The forecasted chance of damaging ground shaking in central Oklahoma is similar to that of natural earthquakes in high-hazard areas of California.
“Most of the damage we forecast will be cracking of plaster or unreinforced masonry. However, stronger ground shaking could also occur in some areas, which could cause more significant damage,” said Petersen.
The new report is valuable for making informed decisions to reduce the nation’s vulnerability and providing safety information to those who may be at risk from strong shaking. For example, the 2016 forecast has been used by engineers to evaluate earthquake safety of buildings, bridges, pipelines and other important structures. Risk modelers have used data in developing new risk assessments, which can be used to better understand potential impacts on insurance premiums. The U.S. Army Corps of Engineers has used the information to provide guidance on updating their safety assessments of selected facilities.
Continuing collaborations between regulators, industry, and scientists will be important toward reducing hazard, improving future forecasts, and enhancing preparedness.
Central versus Western U.S.
In recent years, the CEUS has experienced a significant increase in induced earthquakes. Therefore, in the 2017 and 2016 forecasts, scientists distinguish between human-induced and natural seismicity only for the CEUS. Scientists also used a historical catalog of seismic events dating back to the 1700s, putting a strong emphasis on earthquakes that occurred during the last 2 years.
Future research, noted Petersen, could take a more detailed look at induced seismicity in the west, including in California at The Geysers, Brawley and small areas of the Los Angeles Basin.
Distinguishing Between Induced and Natural Earthquakes
To determine whether particular clusters of earthquakes were natural or induced, the USGS relied on published literature and discussions with state officials and the scientific and earthquake engineering community. Scientists looked at factors such as whether an earthquake occurred near a wastewater disposal well and whether the well was active during the time the earthquakes occurred. If so, it was classified as an induced event.
The one-year outlook is chosen because induced earthquake activity can increase or decrease with time and is subject to commercial and policy decisions that could change rapidly. The 2016 and 2017 forecasts employ identical methodologies; the only difference is that the 2017 forecast includes an updated earthquake catalog with 2016 events. This allows for a direct comparison from one year to the next.
In contrast, the USGS National Seismic Hazard Map assesses natural earthquake hazards and uses a 50-year forecast. That timeframe was chosen because that is the average lifetime of a building, and such information is essential to engineering design and the development of building codes.
The USGS is the only federal agency with responsibility for recording and reporting earthquake activity nationwide and assessing seismic hazard. These maps are part of USGS contributions to the National Earthquake Hazards Reduction Program, which is a congressionally established partnership of four federal agencies with the purpose of reducing risks to life and property in the United States that result from earthquakes.
A powerful nighttime earthquake in the southern Philippines killed at least six people and injured more than 120 others.Saturday, February 11th, 2017
Seismotectonics of the Philippine Sea and Vicinity
The Philippine Sea plate is bordered by the larger Pacific and Eurasia plates and the smaller Sunda plate. The Philippine Sea plate is unusual in that its borders are nearly all zones of plate convergence. The Pacific plate is subducted into the mantle, south of Japan, beneath the Izu-Bonin and Mariana island arcs, which extend more than 3,000 km along the eastern margin of the Philippine Sea plate. This subduction zone is characterized by rapid plate convergence and high-level seismicity extending to depths of over 600 km. In spite of this extensive zone of plate convergence, the plate interface has been associated with few great (M>8.0) ‘megathrust’ earthquakes. This low seismic energy release is thought to result from weak coupling along the plate interface (Scholz and Campos, 1995). These convergent plate margins are also associated with unusual zones of back-arc extension (along with resulting seismic activity) that decouple the volcanic island arcs from the remainder of the Philippine Sea Plate (Karig et al., 1978; Klaus et al., 1992).
South of the Mariana arc, the Pacific plate is subducted beneath the Yap Islands along the Yap trench. The long zone of Pacific plate subduction at the eastern margin of the Philippine Sea Plate is responsible for the generation of the deep Izu-Bonin, Mariana, and Yap trenches as well as parallel chains of islands and volcanoes, typical of circum-pacific island arcs. Similarly, the northwestern margin of the Philippine Sea plate is subducting beneath the Eurasia plate along a convergent zone, extending from southern Honshu to the northeastern coast of Taiwan, manifested by the Ryukyu Islands and the Nansei-Shoto (Ryukyu) trench. The Ryukyu Subduction Zone is associated with a similar zone of back-arc extension, the Okinawa Trough. At Taiwan, the plate boundary is characterized by a zone of arc-continent collision, whereby the northern end of the Luzon island arc is colliding with the buoyant crust of the Eurasia continental margin offshore China.
Along its western margin, the Philippine Sea plate is associated with a zone of oblique convergence with the Sunda Plate. This highly active convergent plate boundary extends along both sides the Philippine Islands, from Luzon in the north to the Celebes Islands in the south. The tectonic setting of the Philippines is unusual in several respects: it is characterized by opposite-facing subduction systems on its east and west sides; the archipelago is cut by a major transform fault, the Philippine Fault; and the arc complex itself is marked by active volcanism, faulting, and high seismic activity. Subduction of the Philippine Sea Plate occurs at the eastern margin of the archipelago along the Philippine Trench and its northern extension, the East Luzon Trough. The East Luzon Trough is thought to be an unusual example of a subduction zone in the process of formation, as the Philippine Trench system gradually extends northward (Hamburger et al., 1983). On the west side of Luzon, the Sunda Plate subducts eastward along a series of trenches, including the Manila Trench in the north, the smaller less well-developed Negros Trench in the central Philippines, and the Sulu and Cotabato trenches in the south (Cardwell et al., 1980). At its northern and southern terminations, subduction at the Manila Trench is interrupted by arc-continent collision, between the northern Philippine arc and the Eurasian continental margin at Taiwan and between the Sulu-Borneo Block and Luzon at the island of Mindoro. The Philippine fault, which extends over 1,200 km within the Philippine arc, is seismically active. The fault has been associated with major historical earthquakes, including the destructive M7.6 Luzon earthquake of 1990 (Yoshida and Abe, 1992). A number of other active intra-arc fault systems are associated with high seismic activity, including the Cotabato Fault and the Verde Passage-Sibuyan Sea Fault (Galgana et al., 2007).
Relative plate motion vectors near the Philippines (about 80 mm/yr) is oblique to the plate boundary along the two plate margins of central Luzon, where it is partitioned into orthogonal plate convergence along the trenches and nearly pure translational motion along the Philippine Fault (Barrier et al., 1991). Profiles B and C reveal evidence of opposing inclined seismic zones at intermediate depths (roughly 70-300 km) and complex tectonics at the surface along the Philippine Fault.
Several relevant tectonic elements, plate boundaries and active volcanoes, provide a context for the seismicity presented on the main map. The plate boundaries are most accurate along the axis of the trenches and more diffuse or speculative in the South China Sea and Lesser Sunda Islands. The active volcanic arcs (Siebert and Simkin, 2002) follow the Izu, Volcano, Mariana, and Ryukyu island chains and the main Philippine islands parallel to the Manila, Negros, Cotabato, and Philippine trenches.
Seismic activity along the boundaries of the Philippine Sea Plate (Allen et al., 2009) has produced 7 great (M>8.0) earthquakes and 250 large (M>7) events. Among the most destructive events were the 1923 Kanto, the 1948 Fukui and the 1995 Kobe (Japan) earthquakes (99,000, 5,100, and 6,400 casualties, respectively), the 1935 and the 1999 Chi-Chi (Taiwan) earthquakes (3,300 and 2,500 casualties, respectively), and the 1976 M7.6 Moro Gulf and 1990 M7.6 Luzon (Philippines) earthquakes (7,100 and 2,400 casualties, respectively). There have also been a number of tsunami-generating events in the region, including the Moro Gulf earthquake, whose tsunami resulted in more than 5000 deaths.
1/23/1556: An estimated 8.3 earthquake in Shaanxi, China, kills an estimated 830,000 people more or less.Monday, January 23rd, 2017
- “…The quake struck in the middle of a densely populated area with poorly constructed buildings and homes, resulting in a horrific death toll…”
WEAK53 PAAQ 220440
Tsunami Information Statement Number 1
NWS National Tsunami Warning Center Palmer AK
840 PM PST Sat Jan 21 2017
…THIS IS A TSUNAMI INFORMATION STATEMENT FOR ALASKA, BRITISH
COLUMBIA, WASHINGTON, OREGON AND CALIFORNIA…
* There is no tsunami danger for the areas listed above.
* Based on the depth of the earthquake a tsunami
is not expected.
* An earthquake has occurred with parameters listed below.
PRELIMINARY EARTHQUAKE PARAMETERS
* The following parameters are based on a rapid preliminary
assessment and changes may occur.
* Magnitude 8.0
* Origin Time 1930 AKST Jan 21 2017
2030 PST Jan 21 2017
0430 UTC Jan 22 2017
* Coordinates 6.1 South 155.2 East
* Depth 104 miles
* Location near the Solomon Islands
ADDITIONAL INFORMATION AND NEXT UPDATE
* Refer to the internet site ntwc.arh.noaa.gov for
* Pacific coastal regions outside California, Oregon,
Washington, British Columbia and Alaska should refer to the
Pacific Tsunami Warning Center messages at ptwc.weather.gov.
* This will be the only U.S. National Tsunami Warning center
message for this event unless additional information becomes
So far only three bodies have been recovered, with reports of a fourth, and two people saved from the 4-star Hotel Rigopiano after earthquakes in the central Italian Abruzzo region appear to have caused the avalanche.Friday, January 20th, 2017
The January 18, 2017 M 5.7 and M 5.6 earthquakes southwest of Amatrice, Italy, occurred as the result of shallow normal faulting on a NW-SE oriented fault (or faults) in the Central Apennines. The Apennines is a mountain range that runs from the Gulf of Taranto in the south to the southern edge of the Po basin in northern Italy. Geologically, the Apennines is largely an accretionary wedge formed as a consequence of subduction. This region is tectonically and geologically complex, involving subduction of the Adria micro-plate beneath Eurasia and the Apennines from east to west, continental collision between the Eurasia and Nubia (Africa) plates building the Alpine mountain belt further to the north, and the opening of the Tyrrhenian basin to the west (the latter of which is in turn related to Adria subduction and eastward trench migration). The evolution of this system has caused the expression of all different tectonic styles acting at the same time in a broad region surrounding Italy and the central Mediterranean. The January 18, 2017 normal faulting earthquakes are intraplate events, an expression of the east-west extensional tectonics that now dominate along the Apennine belt.
The January 18, 2017 earthquakes (09:25 UTC M 5.3; 10:14 UTC M 5.7; 10:25 UTC M 5.6) continue a sequence of damaging earthquakes that include:
– The August 24, 2016, M 6.2 central Italy (Amatrice) earthquake, which caused approximately 300 fatalities, and severely damaged the town of Amatrice.
– The October 26, 2016, M 6.1 central Italy earthquake, which was itself preceded by several hours by a M 5.5 earthquake. The M 6.1 earthquake resulted in damage to numerous buildings, but no fatalities.
– The October 30, 2016, M 6.6 central Italy earthquake, the largest event in the sequence to date. This event caused 20 injuries and left many homeless, and caused extensive damage, including destroying the Basilica of Saint Benedict.
Since the August 24, 2016 M 6.2 earthquake, and prior to January 18, 2017, the USGS has reported 75 events of M 4.0 and larger, including a M 5.6 earthquake within an hour of the August 24, 2016 shock, the two large events on October 26, 2016 – an M 5.5 event at 17:10 UTC, and the M 6.1 earthquake at 19:18 UTC – and the M 6.6 event on October 30, 2016. Both October 26, 2016 events were at the northern end of the aftershock sequence of the M 6.2 August 24, 2016 earthquake. The October 30, 2016, M 6.6 event occurred between the two prior largest earthquakes, approximately 10 km southeast of the October 26, 2016, M 6.1 event. The January 18, 2017 earthquakes occurred at the southern end of the sequence, about 15 km southeast of the M 6.2 August 24, 2016 earthquake.
The central Apennine region has experienced several significant earthquakes in recorded history. The largest instrumentally recorded earthquake within 100 km of the 2016-17 events was the January 13, 1915 M 6.7 earthquake, which was nearly 90 km to the south-southeast of the October 26, 2016 event, near Avezzano. The 1915 earthquake killed approximately 32,000 people. In September 1997, a Mw 6.0 earthquake 35 km west-northwest of the October 30, 2016 event killed 11, injured over 100 and destroyed approximately 80,000 homes in the Marche and Umbria regions. This 1997 event was part of a series of earthquakes known as the Umbria-Marche seismic sequence, which included eight events of magnitude greater than M5.0 in a two-month period between September and November of that year, including the events that substantially damaged the Basilica of St Francis in Assisi. In April 2009, a Mw 6.3 earthquake 60 km to the south-southeast of the October 30, 2016 event, near the town of L’Aquila, killed at least 295, injured over 1,000 and left 55,000 or more homeless. The L’Aquila earthquake resulted in significant landsliding in the local area, and was also followed by a vigorous aftershock sequence, including 5 other events of M 5.0 or larger. The location of the 2016-17 earthquake sequence is predominantly in a gap between the aftershock sequences of the 1997 and 2009 events; the January 18, 2017 events are just to the north of the northern extent of the 2009 sequence.
Further research into this ongoing sequence will more clearly determine how each event relates to other earthquakes, and how the sequence as a whole developed in space and time.