Increase In Earthquake Activity Research Articles

Landslide hazard cascades can trigger earthquakes.

While earthquakes are well-known to trigger surface hazards and initiate hazard cascades, whether surface hazards can instead trigger earthquakes remains underexplored. In 2018, two landslides on the Tibetan plateau created landslide-dammed lakes which subsequently breached and caused catastrophic outburst floods. Here we build an earthquake catalog using machine-learning and cross-correlation-based methods which shows there was a statistically significant increase in earthquake activity (local magnitude ≤ 2.6) as the landslide-dammed lake approached peak water level which returned to the background level after dam breach. We further find that ~90% of the seismicity occurred where Coulomb stress increased due to the combined effect of direct loading and pore pressure diffusion. The close spatial and temporal correlation between the calculated Coulomb stress increase and earthquake activity suggests that the earthquakes were triggered by these landslide hazard cascades. Finally, our Coulomb stress modeling considering the properties of landslide-dammed lakes and reservoir-induced earthquakes globally suggests that earthquake triggering by landslide-dammed lakes and similar structures may be a ubiquitous phenomenon. Therefore, we propose that earthquake-surface hazard interaction can include bidirectional triggering which should be properly accounted for during geological hazard assessment and management in mountainous regions.

Improvement of liquefaction potential in saturated sandy soil by CKD and bentonite

AbstractDue to the increase in earthquake activity in Iraq and Middle East during the last two decades, the study and understanding of probable destructive action and the best method to mitigate this effect became more important. So, many improvements and mitigation methods can be used. In this study, the use of permeation grout technique was adopted to prevent the existing soil condition in urban area by using cement kiln dust and bentonite clay. The tests were executed by using 1 g shaking table apparatus to simulate a sinusoidal motion (vibration) at specified different frequencies. The liquefaction phenomena were observed for loose saturated sand at 60 s, 25 s, and 10 s for 0.5 Hz, 0.75 Hz, and 1 Hz, respectively. After mitigation process, the soil liquefaction did not occur until 100 s, 60 s, and 30 s, for the same mentioned frequencies. Besides, the use of cement kiln dust decreases the liquefaction potential and increase the factor of safety.

Seismic behavior of a strengthened full scale reinforced concrete building using the finite element modelling approach

In Iraq, the increase in earthquake activity was observed, but most of the existing buildings can still suffer from severe injury or destruction, and therefore can cause major issues. In this paper, we performed numerically analyses by experimental modeling to demonstrate efficiency using final element analysis (FEA) in the development of modern solutions (FEA) in the development of modern solutions to maintain existing structures from the risk of earthquakes. Using ABAQUS software that supports dynamic analysis, and uses this model to use models for several ways to enhance the earthquake center. This model was a large-scale 4 building tested using a doctor dynamic test (PSD). Experimental models were performed by extending RC walls with various connectivity details in existing buildings to comply with gravity design only for this building. The goal of this study was to determine the impact of adding an above RC wall as a way of modernization, including the design of Dowels and their contribution to the new mouse wall's connection to the existing RC buildings. These enhancements are performed by converting the selected compartment to the new inlet wall RC [2]. The result of analysis modeling is 4.11% of the proportion of differences in the X direction in the upper layer displacement of Abaqus software and the experimental test of Elsa results, and 2.15% of the negative direction X is 4.11%. an accurate similarity and exact building modeling. After verification process, three earthquake enhancement methods are used Next analysis.

Assessment for Seismic Activities in Pesisir Selatan West Sumatra in 2018

The tendency of the recurring earthquake phenomenon in the same place in an area with a high seismic level has triggered an increase in earthquake activity in the region. Kabupaten Pesisir Selatan, which is located in West Sumatra Province, is a coastal area that is very close to the waters of the Sumatran sea as well as a source of destructive earthquakes that hit Sumatra. To anticipate the risk of future earthquakes and as an effort to increase public awareness and preparedness in the South Coast, in particular, it is necessary to provide understanding and knowledge of the seismic activities that have occurred there. The research method was carried out by collecting earthquake event data in the South Coast region for the period of January - December 2018 from the United States Geological Survey (USGS) data. The results of the analysis concluded, that in the Pesisir Selatan District there were frequent tectonic earthquakes, and also followed by landslides due to the contours of many hilly areas.

Temporal variation in the magnitude‐frequency distribution during the Guy‐Greenbrier earthquake sequence

AbstractThe recent increase in earthquake activity in the central U.S. has led to concerns about the hazard posed by induced earthquakes. Understanding earthquake phenomena and monitoring in all settings can be improved by the detection of small events; however, the catalog of induced earthquakes is incomplete for small events due to the sparse instrumentation. This is particularly true in settings of low background seismicity, like the central U.S. We apply single‐station template matching to detect small earthquakes during the Guy‐Greenbrier sequence in central Arkansas and find over 100 times more earthquakes than are registered in the Advanced National Seismic System catalog between July 2010 and October 2011. A complete catalog over nearly 4 units of magnitude enables us to analyze the magnitude‐frequency distribution of induced earthquakes. We find that earthquakes deviated from the Gutenberg‐Richter statistics during the operation of nearby injection wells but returned to Gutenberg‐Richter statistics after the wells were shut in.

Surface Microseismic Monitoring of Hydraulic Fracturing of a Shale-Gas Reservoir Using Short-Period and Broadband Seismic Sensors

Online Material: Figure, table with double‐difference event locations. Hydraulic fracturing has been widely applied in development of tight sand and shale gas reservoirs, in which high‐pressure fluids are injected into target zones to enhance the reservoir permeability so that gas can be more efficiently recovered. The opening and growing of tensile fractures, as well as shearing slip along fractures during stimulation treatment are thought to be the major mechanisms inducing microseismic events around the treatment well (Shemeta and Anderson, 2010). Therefore, microseismic monitoring is a valuable approach to assess the fracturing process. For example, the locations of microseismic events are used to determine fracture network geometry, and their focal mechanisms are helpful for understanding how the fractures are stimulated. The information derived from microseismic monitoring is helpful for reservoir simulation and assessment (e.g., Rutledge and Phillips, 2003; Warpinski, 2009; Maxwell, 2010). However, injecting fluids into underground formations, especially wastewater disposal into deep wells, has caused felt or damaging earthquakes with magnitudes larger than 4 in some cases (Ellsworth, 2013). The well‐documented cases include Rocky Mountain Arsenal in the 1960s (Healy et al. , 1968), wastewater disposal in Texas (Frohlich et al. , 2011), Oklahoma (Holland, 2013), and Arkansas (Horton, 2012). In fact, an anomalous increase in earthquake activity has occurred in the central and eastern United States over the past few years, which is mainly due to deep injection of low‐pressure wastewater into deep strata or basement formations (Ellsworth, 2013). Hydraulic fracturing using high‐pressure fluids can induce a lot of earthquakes, …

Seismic Response of the Katmai Volcanoes to the 6 December 1999 Magnitude 7.0 Karluk Lake Earthquake, Alaska

A sudden increase in earthquake activity was observed beneath volcanoes in the Katmai area on the Alaska Peninsula immediately following the 6 December 1999 magnitude ( M W) 7.0 Karluk Lake earthquake beneath southern Kodiak Island, Alaska. The observed increase in earthquake activity consisted of small ( M L < 1.3), shallow ( Z < 5.0 km) events. These earthquakes were located beneath Mount Martin, Mount Mageik, Trident Volcano, and the Katmai caldera and began within the coda of the Karluk Lake mainshock. All of these earthquakes occurred in areas and magnitude ranges that are typical for the background seismicity observed in the Katmai area. Seismicity rates returned to background levels 8 to 13 hours after the Karluk Lake mainshock. The close temporal relationship with the Karluk Lake mainshock, the onset of activity within the mainshock coda, and the simultaneous increase beneath four separate volcanic centers all suggest these earthquakes were remotely triggered. Modeling of the Coulomb stress changes from the mainshock for optimally oriented faults suggests negligible change in static stress beneath the Katmai volcanoes. This result favors models that involve dynamic stresses as the mechanism for triggered seismicity at Katmai.

Induced earthquakes accompanying the water injection experiment at the Nojima fault zone, Japan: Seismicity and its migration

The 1995 Hyogo‐ken Nanbu (Kobe) earthquake of M7.2 occurred on January 17, 1995. After the earthquake, a scientific drilling program called the Nojima Fault Zone Probe was carried out at the Nojima fault which ruptured during the mainshock. Water was injected during two periods, February 9–13 and March 16–25, 1997. The pumping pressure at the surface was about 4 MPa. Pressurized water was injected into a 1800‐m‐deep borehole and supplied to the surrounding rock at depths between 1480 and 1670 m. The total amount of injected water was 258 m3. An increase in earthquake activity was observed 4 or 5 days after the beginning of each water injection. The seismicity increased in the region around 3 or 4 km from the injection point. This suggests that these earthquakes are likely to have been induced by the water injections. The induced earthquakes were located between 2 and 4 km in depth and had magnitudes ranging from −2 to +1. The hypocenters of the induced earthquakes migrated with speeds of ∼2–40 m/h. The speeds decreased with time, suggesting a relationship with the diffusion of water. Values of intrinsic permeability of 10−14–10−15 m2 were obtained from the time dependency of induced seismicity change. The coefficient of friction in the area where the induced earthquakes occurred was estimated to be less than 0.3. Twenty earthquake clusters were found, and cross‐spectrum analysis was applied to them. We could distinguish between the induced and noninduced earthquakes from the analysis. The induced earthquakes forming each cluster migrated with speeds of 20–80 m/h, which means microscale water migration or permeation. The present water injection experiment revealed that the Nojima fault zone was highly permeable and could slip with small (∼10% or less) increases in pore fluid pressure or shear stress.

Seismotectonic structures along the Savannah River Corridor, South Carolina, U.S.A.

The Savannah River Corridor is defined herein to extend from the Brevard zone in South Carolina to just northwest of Charleston, South Carolina. The length of the Corridor is 400 km, the width 300 km, and the strike is S 40°E. The Corridor includes (1) the Savannah River Site, which is the locus of the most detailed seismic reflection data set in the eastern United States, and is the keystone for the extrapolation of regional reflection seismic data away from the Site, and (2) the South Carolina–Georgia seismic zone. The principal data used for the conclusions of this study are reflection seismic data acquired by the Consortium for Continental Reflection Profiling (COCORP), the Appalachian Ultra-Deep Core Hole (ADCOH) project, and Conoco, Inc. (SRS). Relatively higher seismicity appears to be associated with a crustal scale antiform that has been imaged in the Savannah River Corridor as well as to the northeast along strike in Virginia. An increase in earthquake activity occurs in that part of the crystalline allochthon that overlies and conceals a foreland-dipping imbricate stack that has developed in early Paleozoic rocks beneath the overthrust Piedmont crystalline allochthon. To the southeast, hypocenters of two SRS earthquakes (1985 and 1988), projected along the strike of the Pen Branch northwest-bounding fault of the Dunbarton Triassic rift basin plot on a highly reflective southeastward-dipping shear zone that underlies the basin. Here, the proximity of the hypocenters to the border fault of the Dunbarton basin suggests that syntectonic structures associated with the Pen Branch border fault might be involved. Some of the seismicity is probably associated with reactivation of older Paleozoic and Mesozoic structures.

Remotely triggered seismicity inferred from Taiwan Regional Catalog

The June 1992 Landers (California) earthquake triggered an increase in earthquake activity at distances up to 1250 km. It posed the question whether the remote triggering was really widespread in nature. To check this, we use the regional catalog of seismicity in Taiwan where twelve large 6.0 ≤ MD ≤ 6.5 seismic events took place over the last twenty years. We calculate the number of MD ≥ 2.0 earthquakes, as well as the number of MD ≥ 4.5 earthquakes, starting 15 days prior to and ending 15 days after each MD ≥ 6.0 event. The small‐magnitude activity does not respond to the occurrence of a very large event. However, in 9 out of 12 cases, more MD ≥ 4.5 earthquakes occurred after a large event than in the same time interval before. The number of additional events is proportional to the size of the triggering earthquake. Thus, these extra events are possibly remotely triggered.

The 1994 Northridge earthquake sequence in California: Seismological and tectonic aspects

The Mw 6.7 Northridge earthquake occurred on January 17, 1994, beneath the San Fernando Valley. Two seismicity clusters, located 25 km to the south and 35 km to the north‐northwest, preceded the mainshock by 7 days and 16 hours, respectively. The mainshock hypocenter was relatively deep, at 19 km depth in the lower crust. It had a thrust faulting focal mechanism with a rake of 100° on a fault plane dipping 35° to the south‐southwest and striking N75°W. Because the mainshock did not rupture the surface, its association with surficial geological features remains difficult to resolve. Nonetheless, its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the Transverse Ranges. The Northridge earthquake is part of the temporal increase in earthquake activity in the Los Angeles area since 1970. The mainshock was followed by an energetic aftershock sequence. Eight aftershocks of M ≥ 5.0 and 48 aftershocks of 4 ≤ M ≤ 5 occurred between January 17 and September 30, 1994. The aftershocks extend over most of the western San Fernando Valley and Santa Susana Mountains. They form a diffuse spatial distribution around the mainshock rupture plane, illuminating a previously unmapped thrust ramp, extending from 7–10 km depth into the lower crust to a depth of 23 km. No flattening of the aftershock distribution is observed near its bottom. At shallow depths, above 7–10 km, the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults. The dip of the ramp increases from east to west. The west side of the aftershock zoae is characterized by a dense, steeply dipping, and north‐northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting. These events coincided with the Gillibrand Canyon lateral ramp. Along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms. The focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks, with some strike‐slip and normal faulting in the smaller aftershocks. The 1971 San Fernando and the 1994 Northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge. Both earthquakes accommodated north‐south contractional deformation of the Transverse Ranges. The two earthquakes differ primarily in the dip direction of the faults and the depth of faulting. The 1971 north‐northeast trend of left‐lateral faulting (Chatsworth trend) was not activated in 1994.

Emission rates of sulfur dioxide and carbon dioxide from Redoubt Volcano, Alaska during the 1989–1990 eruptions

Airborne measurements of sulfur dioxide emission rates in the gas plume emitted from fumaroles in the summit crater of Redoubt Volcano were started on March 20, 1990 using the COSPEC method. During the latter half of the period of intermittent dome growth and destruction, between March 20 and mid-June 1990, sulfur dioxide emission rates ranged from approximately 1250 to 5850 t/d, rates notably higher than for other convergent-plate boundary volcanoes during periods of active dome growth. Emission rates following the end of dome growth from late June 1990 through May 1991 decreased steadily to less than 75 t/d. The largest mass of sulfur dioxide was released during the period of explosive vent clearing when explosive degassing on December 14–15 injected at least 175,000 ± 50,000 tonnes of SO 2 into the atmosphere. Following the explosive eruptions of December 1989, Redoubt Volcano entered a period of intermittent dome growth from late December 1989 to mid-June 1990 during which Redoubt emitted a total mass of SO 2 ranging from 572,000 ± 90,000 tonnes to 680,000 ± 90,000 tonnes. From mid-June 1990 through May 1991, the volcano was in a state of posteruption degassing into the troposphere, producing approximately 183,000 ± 50,000 tonnes of SO 2. We estimate that Redoubt Volcano released a minimum mass of sulfur dioxide of approximately 930,000 tonnes. While COSPEC data were not obtained frequently enough to enable their use in eruption prediction, SO 2 emission rates clearly indicated a consistent decline in emission rates between March through October 1990 and a continued low level of emission rates through the first half of 1991. Values from consecutive daily measurements of sulfur dioxide emission rates spanning the March 23, 1990 eruption decreased in the three days prior to eruption. That decrease was coincident with a several-fold increase in the frequency of shallow seismic events, suggesting partial sealing of the magma conduit to gas loss that resulted in pressurization of the shallow magma system and an increase in earthquake activity. Unlike the short-term SO 2 decrease in March 1990, the long-term decrease of sulfur dioxide emission rates from March 1990 through May 1991 was coincident with low rates of seismic energy release and was interpreted to reflect gradual depressurization of the shallow magma reservoir. The long-term declines in seismic energy release and in SO 2 emission rates led AVO scientists to conclude on April 19, 1991 that the potential for further eruptive activity from Redoubt Volcano had diminished, and on this basis, the level of concern color code for the volcano was changed from code yellow ( Volcano is restless; earthquake activity is elevated; activity may include extrusion of lava) to code green ( Volcano is in its normal ‘dormant’ state).

Recent geophysical investigation at Somma-Vesuvio volcanic complex

Activity at Somma-Vesuvio volcanic area in southern Italy is monitored by seismic stations and periodic geodetic and gravity surveys. The seismic network, which consists at present of four vertical stations and one three-component station, recorded an increase in earthquake activity in 1978 and between November 1988 and March 1989. During the later activity, earthquakes were located in a cluster about 3 km beneath the summit of the volcano. Two tide gauges, two tiltmeters and a recording gravimeter are also operating at Somma-Vesuvio. Yearly levelling surveys are conducted along several closed routes that extend from as much as 6 km from the base of the volcano to the summit area. Survey results reveal no significant ground movement since 1959, except for a slight subsidence around the rim of the summit crater. Gravity changes have been larger than the expected 10 μGal uncertainty of the measurements. The lack of contemporary elevation changes implies that the observed gravity changes are the result of a slight change in density structure. The cone of Somma-Vesuvio has been very stable for the last few decades, showing no indications of a buildup to activity. The lack of surface movement should rule out a magma-supply rate to this volcano at the historic eruptive rate of 0.002 km 3/yr.

Seismicity Remotely Triggered by the Magnitude 7.3 Landers, California, Earthquake

The magnitude 7.3 Landers earthquake of 28 June 1992 triggered a remarkably sudden and widespread increase in earthquake activity across much of the western United States. The triggered earthquakes, which occurred at distances up to 1250 kilometers (17 source dimensions) from the Landers mainshock, were confined to areas of persistent seismicity and strike-slip to normal faulting. Many of the triggered areas also are sites of geothermal and recent volcanic activity. Static stress changes calculated for elastic models of the earthquake appear to be too small to have caused the triggering. The most promising explanations involve nonlinear interactions between large dynamic strains accompanying seismic waves from the mainshock and crustal fluids (perhaps including crustal magma).

First results from a new seismographic network in Costa Rica, central America

Abstract The occurrence of past large earthquakes in space and time has been useful in estimating locations and repeat times for similar future events (Kelleher et al. , 1973; and McCann et al. , 1979). The lack of major energy release in and near Costa Rica during the last 30 years (i.e., seismic slip deficiency, as shown by McNally and Minster, 1981), and a recent increase in earthquake activity motivated the organization and installation of a permanent seismographic network. The network became operational in early 1984 with financial support from the Office of Foreign Disaster Assistance (OFDA, USAID). The Costa Rica network will provide the data to help understand the nature of the tectonic interaction of the Cocos and Caribbean plates and to evaluate the potential for present and future earthquake hazards in light of the historical earthquake activity.

Microearthquake activity in Eastern Nevada and death valley California before and after the nuclear explosion Benham

abstract Six portable, high-gain, high-frequency seismographs were operated in Nevada and California for several weeks before and after the underground nuclear explosion Benham to assess the possibility that earthquakes at distances of tens of kilometers or more may be triggered by large underground explosions. A pronounced increase in earthquake activity in the vicinity of the shot point was observed immediately after the detonation and continued for more than a month after the explosion. No significant change in activity within 25 km of any of our instruments northeast of the Nevada Test Site was observed, and the activity in Death Valley recorded after the explosion did not indicate an important increase. These data imply that this particular explosion did not significantly affect the seismicity of the region studied. Throughout the period of observation the seismic activity northeast of the Nevada Test Site was low; an average of about one event per day was detected within about 25 km of each station. This suggests that the current tectonic activity of this part of Nevada is lower than that of western Nevada and of most other tectonically active regions where microearthquake studies have been made.