Seismic Quiescence Research Articles

Late Holocene uplift of Rhodes, Greece: evidence for a large tsunamigenic earthquake and the implications for the tectonics of the eastern Hellenic Trench System

Several large earthquakes in the Hellenic subduction zone have been documented in historical records from around the eastern Mediterranean, but the relative seismic quiescence of the region over the period of instrumental observation means that the exact locations of these earthquakes and their tectonic significance are not known. We present AMS radiocarbon dates from uplifted late Holocene palæoshorelines from the island of Rhodes, showing that uplift is most consistent with a single large (MW ≥ 7.7) reverse-faulting earthquake between about 2000 BC and 200 BC. Analysis of the uplift treating the earthquake as a dislocation in an elastic half-space shows a predominantly reverse-faulting event with a slip vector oblique to the direction of convergence between Rhodes and Nubia. We suggest that the fault responsible for the uplift dips at an angle of 30–60° above the more gently dipping oblique subduction interface. The highly oblique convergence across the eastern Hellenic plate boundary zone appears to be partitioned into reverse slip on faults that strike parallel to the boundary and strike-parallel or oblique slip on the subduction interface. Hydrodynamical simulation of tsunami propagation from a range of tectonically plausible sources suggests that earthquakes on the fault uplifting Rhodes represent a significant tsunami hazard for Rhodes and SW Turkey, and also possibly for Cyprus and the Nile Delta.

Spatial Variation of Fractal Parameters in Central Alborz, Iran

Baladeh-Kojour earthquake of May 28th, 2004 is one of the largest earthquakes in vicinity of Tehran, occurred in the northern part of the Alborz range. In this research, spatial variation of fractal parameters has been studied to estimate the seismic pattern of the study area. In order to draw the spatial variation maps, b-value, correlation dimension of epicentral and temporal distribution of earthquakes, De and Dt have been calculated for the data sets of before and after the mainshock, separately. The results show that before the earthquake, these parameters have low values in the eastern side of the mainshock epicenter. It seems that these low values before the earthquake may arise due to clusters of events with larger magnitude and small events after it. Seismic rate has decreased in the surroundings of the mainshock (seismic quiescence). After the mainshock, the lowest values of b-value and Dt is seen in the epicentral and western part of the mainshock. These low values are due to aftershock clustering and stress release, took placed just after the mainshock and during the aftershock sequence. Intensity increasing is observed in the shake map of earthquake. The De parameter is low after the mainshock occurrence. Low b-value and high De indicate high level of seismic activity in the region. The obtained results show the fractal parameters sensitivity to spatial and temporal clustering of earthquakes. Therefore, these parameters can be used as an indicator for seismic precursory patterns of major earthquakes.

The Mw 7.8 April 25, 2015 Nepal earthquake (End of a long-term seismic quiescence?)

The Mw 7.8 April 25, 2015 Nepal earthquake (End of a long-term seismic quiescence?)

Hydraulic fracturing and the Crooked Lake Sequences: Insights gleaned from regional seismic networks

AbstractWithin central Alberta, Canada, a new sequence of earthquakes has been recognized as of 1 December 2013 in a region of previous seismic quiescence near Crooked Lake, ~30 km west of the town of Fox Creek. We utilize a cross‐correlation detection algorithm to detect more than 160 events to the end of 2014, which is temporally distinguished into five subsequences. This observation is corroborated by the uniqueness of waveforms clustered by subsequence. The Crooked Lake Sequences have come under scrutiny due to its strong temporal correlation (>99.99%) to the timing of hydraulic fracturing operations in the Duvernay Formation. We assert that individual subsequences are related to fracturing stimulation and, despite adverse initial station geometry, double‐difference techniques allow us to spatially relate each cluster back to a unique horizontal well. Overall, we find that seismicity in the Crooked Lake Sequences is consistent with first‐order observations of hydraulic fracturing induced seismicity.

A High Resolution Aftershock Catalog of the Magnitude 7.5 Craig, Alaska, Earthquake on 5 January 2013

Abstract The M w 7.5 Craig, Alaska, earthquake on 5 January 2013 was the second largest earthquake on the Queen Charlotte fault (QCF) in 40 yrs, representing the transform plate boundary between the Pacific and North American plates. Earthquake hazard along the QCF was known from historical earthquakes, but the absence of major earthquakes in the digitally instrumented era has limited studies of earthquakes. Here, we present an analysis of aftershocks of the Craig earthquake. We first use waveform cross correlation and double‐difference relative relocation to relocate the aftershock catalog of the Alaska Earthquake Center (AEC). Our relocated catalog reveals a complex fault structure activated in response to the mainshock and provides insight into the faulting mechanics of this graduated transpressive plate boundary. We then use network‐matched filtering (NMF) to detect additional aftershocks. Using 351 aftershocks located by the AEC in 2013 as template events, we identify 1785 aftershocks through May 2013. This is a greater than fivefold increase in aftershock detection rate compared with the standard single‐event network processing. Utilizing regional seismic stations and waveform modeling, we are able to characterize the faulting parameters for 12 aftershocks. Six aftershocks show focal mechanisms consistent with the mainshock faulting parameters, and six aftershocks show either thrust or strike‐slip mechanisms with nodal planes rotated ∼45° from the mainshock mechanism. The six aftershocks that are inconsistent with the QCF have P axes that are perpendicular to the plate boundary, suggesting that transpression remains at this location. We show that five of these large aftershock families were activated within a day of the mainshock, whereas seven families were delayed by multiple days before activating. We show evidence for migrating patterns of seismic quiescence and elevated seismicity, relative to the predicted Omori–Utsu decay, which is related to the largest aftershock in the sequence. Online Material: Aftershock catalog of the 5 January 2013 Craig, Alaska, earthquake.

Geomorphology reveals active décollement geometry in the central Himalayan seismic gap

The similar to 700-km-long ``central seismic gap'' is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200-500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue for a great earthquake. Despite the region's recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly understood. Here, we place new constraints on the spatial distribution of rock uplift within the western similar to 400 km of the central seismic gap using topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic Be-10. The data sets show a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the decollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.

A Long‐Term Seismic Quiescence before the 2004 Sumatra (Mw 9.1) Earthquake

The 2004 Sumatra ( M w 9.1) earthquake was preceded by a seismic quiescence that began 13 years before the mainshock. An earthquake catalog created by the International Seismological Centre is analyzed in the study area, 80°–110° E, 10° S–20° N, between 1964 and 2004, including 1153 earthquakes shallower than 100 km with body‐wave magnitude of 5.0≤ m b≤6.7. A detailed analysis of the earthquake catalog using a gridding technique (ZMAP) shows the quiescent area is located between 3° and 6° N, which covers the southeastern part of the focal area, including the rupture initiation point of the 2004 Sumatra earthquake. The observed spatial pattern of quiescence can be explained by stress perturbation due to a long‐term slow slip located on the deeper edge of the mainshock fault, which is predicted by a numerical simulation based on a laboratory‐derived friction law. Although the quiescence is not significant statistically, it may still be considered unlikely that such an anomalous quiescence would occur at almost the same time and location as other long‐term anomalies reported in the previous studies, including decreases in b ‐value and tidal triggering.

Patterns of significant seismic quiescence on the Mexican Pacific coast

Many authors have proposed that the study of seismicity rates is an appropriate technique for evaluating how close a seismic gap may be to rupture. We designed an algorithm for identification of patterns of significant seismic quiescence by using the definition of seismic quiescence proposed by Schreider (1990). This algorithm shows the area of quiescence where an earthquake of great magnitude may probably occur. We have applied our algorithm to the earthquake catalog on the Mexican Pacific coast located between 14 and 21degrees of North latitude and 94 and 106degrees West longitude; with depths less than or equal to 60km and magnitude greater than or equal to 4.3, which occurred from January, 1965 until December, 2014. We have found significant patterns of seismic quietude before the earthquakes of Oaxaca (November 1978, Mw=7.8), Petatlán (March 1979, Mw=7.6), Michoacán (September 1985, Mw=8.0, and Mw=7.6) and Colima (October 1995, Mw=8.0). Fortunately, in this century earthquakes of great magnitude have not occurred in Mexico. However, we have identified well-defined seismic quiescences in the Guerrero seismic-gap, which are apparently correlated with the occurrence of silent earthquakes in 2002, 2006 and 2010 recently discovered by GPS technology.

Spatial-temporal analysis of seismicity before the 2012 Varzeghan, Iran, Mw 6.5 earthquake

In this work, the spatial and temporal variations of seismicity in northwestern Iran have been evaluated with a special focus on seismic precursors of the 11 August 2012 Mw 6.5 Varzeghan earthquake. The precursors are defined by the z-value test and the generalized fractal dimensions of earthquake epicenters. The investigation applies earthquakes that have occurred since 2006 in a region that includes the main shock and collected by the Iranian Seismological Center. In order to eliminate the effect of explosions in the processing, we removed the explosion from the used catalog by using the normalized ratio analysis of daytime to nighttime events. Having done the preprocessing procedures, we removed the events with magnitudes of less than 2.5. As a result of our analysis, a period of seismic quiescence has been identified, which started about 3 years before the Varzeghan main shock. In a nice coincidence with these results, significant changes have been observed in the generalized fractal dimensions and the related spectra prior to the occurrence of the Varzeghan earthquake. The changes indicate that the seismic activities of the studied area have had increasingly dense clustering in space since about mid-2009, which suggests the regional preparedness for the occurrence of the main quake. Furthermore, the analysis did not exhibit any significant seismic quiescence anomaly at the beginning of 2013.

A study on the correlations between seismotectonic b-value and Dc-value, and seismic quiescence Z-value in the Western Anatolian region of Turkey

A study on the correlations between seismotectonic b-value and Dc-value, and seismic quiescence Z-value in the Western Anatolian region of Turkey

The association of micro‐earthquake clusters with mapped faults in the Dead Sea basin

AbstractAbout 1100 micro‐earthquakes that occurred along the Dead Sea basin during the past 25 years express ongoing seismic activity along mostly obscured fault segments. We apply seismological and statistical methods in order to associate seismic activity with geological and geophysical data and to locate and characterize active fault segments in the basin; three regional 1‐D velocity models and the double‐difference method were used for the relocation of seismic events. Geostatistical analysis shows that in first order the micro‐earthquakes reflect faulting along segments of the main longitudinal fault while seismic quiescence along historically active zones indicates locked segments and stress concentration. Based on waveform similarity, spatial and temporal proximity, we define earthquake clusters that comprise about 30% of the relocated seismicity and two thirds of the total seismic moment. About 80% of the clusters are associated with N‐S trending faults. In two cases the clusters indicate a migration of the seismicity in time and space, one of which preceded the largest earthquake in our catalog (M5.2). In addition to the associated longitudinal activity, several clusters appear to represent faulting in east‐west orientation which is interpreted here as a secondary fault system.

Seismicity change revealed by ETAS, PI, and Z-value methods: A case study of the 2013 Nantou, Taiwan earthquake

On Mar. 27, 2013, a ML6.2 earthquake occurred in the Nantou area of central Taiwan, which caused one death and nearly 90 injured. Two months later, another ML6.3 earthquake struck the same region on June 2, 2013, the epicenter of which is close to the March ML6.2 earthquake. Seismicity is a sensitive indicator of stress rate and inelastic deformation process in crust. Therefore, examination of temporal changes in seismicity is important to understand the preparatory processes of damaging inland earthquakes. In this study, we applied the Epidemic-Type Aftershock-Sequences model (ETAS model) to the earthquake data covering broader Taiwan region, which is maintained by the Central Weather Bureau (CWB) of Taiwan, to investigate precursory temporal changes in seismicity for the ML6.2 Nantou earthquake. We regard the March ML6.2 and June ML6.3 earthquakes as an event sequence and especially focus on temporal changes in seismicity prior to the ML6.2 event. Application of more than one model to an earthquake catalog would be informative in elucidating the relationships between seismicity precursors and the preparatory processes of large earthquakes. Based on this motivation, we further applied two different approaches: the pattern informatics (PI) method and the ZMAP method, which is a gridding technique based on the standard deviate (Z-value) test to the same earthquake data of CWB. As a result, we found that the epicenter of the 2013 ML6.2 Nantou earthquake was surrounded by three main seismic quiescence regions prior to its occurrence. The assumption that this is due to precursory slip (stress drop) on fault plane or its deeper extent of the ML6.2 Nantou earthquake is supported by previous researches based on seismicity data, geodedic data, and numerical simulations using rate- and state-dependent friction laws.

Variations in the intensity of the global seismic process in the 20th and the beginning of 21st centuries

The variations in the intensity of the global seismic process during the 20th and beginning of the 21st centuries are analyzed. It is established that the evolution of the global seismic process is marked by a trend of a certain quasi-periodicity in the release of seismic energy. The analysis of the lithospheric seismicity during 113 years has shown that this time interval accommodated three periods of seismic activation separated by two periods of relative seismic quiescence. The global seismicity of the Earth is strongly dominated by the contributions of the earthquakes in the Pacific seismic belt. A considerable effect is also provided by the northeastern margin of the Indian Ocean. The horizontal displacements of the lithospheric plates are probably responsible for the accumulation of stresses in the potential sources of the earthquakes at the interplate contacts and in the orogenic areas inside the continents. The revealed clustering of the earthquakes with M ≥ 8.3 in the narrow time intervals is probably due to the fact that the strongest seismic event that occurs at the beginning of each activation is a trigger which simultaneously causes the relaxation of a few dozen mature potential sources within 10–15 years. This interval of seismic activation is followed by a relatively quiet period of 30–35 years, when the energy for the next activation is accumulated in a series of high-magnitude sources.

The Earthquake Cycle in the San Francisco Bay Region: A.D. 1600-2012

Abstract Stress changes produced by the 1906 San Francisco earthquake had a profound effect on the seismicity of the San Francisco Bay region (SFBR), dramatically reducing it in the twentieth century. Whether the SFBR is still within or has emerged from this seismic quiescence is an issue of debate with implications for earthquake mechanics and seismic hazards. Historically, the SFBR has not experienced one complete earthquake cycle (i.e., the accumulation of stress, its release primarily as coseismic slip during surface‐faulting earthquakes, its re‐accumulation in the interval following, and its subsequent rerelease). The historical record of earthquake occurrence in the SFBR appears to be complete at about M 5.5 back to 1850 (Bakun, 1999). For large events, the record may be complete back to 1776, which represents about half a cycle. Paleoseismic data provide a more complete view of the most recent pre‐1906 SFBR earthquake cycle, extending it back to about 1600. Using these, we have developed estimates of magnitude and seismic moment for alternative sequences of surface‐faulting paleoearthquakes occurring between 1600 and 1776 on the region’s major faults. From these we calculate seismic moment and moment release rates for different time intervals between 1600 and 2012. These show the variability in moment release and suggest that, in the SFBR regional plate boundary, stress can be released on a single fault in great earthquakes such as that in 1906 and in multiple ruptures distributed on the regional plate boundary fault system on a decadal time scale.

Ring structures of seismicity in central Tien Shan and Dzungaria: Possible precursory processes of large earthquakes

It is shown that episodes of comparative seismic quiescence that lasted about 20–25 years in the areas of study alternated with intervals of sharply increased seismicity as series of large (M ≥ 6.9) earthquakes occurred during two to three decades. Since no M ≥ 6.6 earthquake has occurred in the area for as long as 21 years after the 1992 Susamyr event, middle-term prediction would require identification of zones of imminent large earthquakes. More reliable identification of such zones rests on data relating to inhomogeneities in the field of S-wave attenuation in the lithosphere, as well as on the characteristics of ring structures of seismicity. Such structures are formed as zones of seismic quiescence that are bounded by M ≳ Mth earthquake epicenters, where Mth is the threshold magnitude value. Correlative relationships were previously derived, lgL(Mw) and Mth(Mw), for events with different focal mechanisms (L is the length of the longer axis of a seismicity ring and Mw is the magnitude of the associated large earthquake). These relationships were used to estimate the Mw of large events that can occur in these ring structures. The greatest earthquake with Mw ≳ 7.5 is probably about to occur in southern Tien Shan, east of the 1949 Khait earthquake rupture. A smaller event (Mw ∼ 7.0) can occur in the Kyrgyz Range area. Still smaller earthquakes probably have their precursory areas north and east of Lake Issyk-Kul, as well as in Dzungaria.

Seismicity Pattern Changes before theM= 4.8 Aeolian Archipelago (Italy) Earthquake of August 16, 2010

We investigated the seismicity patterns associated with an M = 4.8 earthquake recorded in the Aeolian Archipelago on 16, August, 2010, by means of the region-time-length (RTL) algorithm. This earthquake triggered landslides at Lipari; a rock fall on the flanks of the Vulcano, Lipari, and Salina islands, and some damages to the village of Lipari. The RTL algorithm is widely used for investigating precursory seismicity changes before large and moderate earthquakes. We examined both the spatial and temporal characteristics of seismicity changes in the Aeolian Archipelago region before the M = 4.8 earthquake. The results obtained reveal 6-7 months of seismic quiescence which started about 15 months before the earthquake. The spatial distribution shows an extensive area characterized by seismic quiescence that suggests a relationship between quiescence and the Aeolian Archipelago regional tectonics.

Seismic quiescence and activation anomalies from 2005 to 2008 beneath the Kanto district, central Honshu, Japan

In the present study, an earthquake catalog is used that lists 1,197 earthquakes with M ≥ 3.9. All of the earthquake waveforms were recorded by the Earthquake Research Institute, University of Tokyo. These waveforms have been manually re-examined, and hypocenters and magnitudes re-calculated. A detailed analysis of the re-determined earthquake catalog between 1996 and 2007, using a gridding technique (ZMAP), shows a pair of seismic quiescence and activation anomalies that start around the middle of 2005, and last about 30 months. The pair of quiescence and activation anomalies are located very close to each other, and the Z-values are +5.0 and −3.8 for a time window of T w = 1.5 years, using a sample size of N = 100 earthquakes. The anomaly pair is not a coincidence as is confirmed by a numerical simulation with the assumption of random seismicity. One possible hypothesis is presented to explain the seismicity anomaly: a long-term slow slip event (LSSE) occurs on the upper boundary of the subducting Pacific plate, and the seismic quiescence and activation anomalies are caused by the Coulomb failure stress change associated with the LSSE.

Temporal variations of seismicity parameters in the Central Alborz, Iran

Temporal changes of b-value, fractal (correlation) dimensions of epicenters (D e ) and occurrence time of earthquakes (D t ) and relations between these parameters were calculated to investigate precursory changes before 28 May 2004, Baladeh-Kojour earthquake (M w = 6.3) of Central Alborz, Iran. 2086 events with M N ≥ 1.7 were selected for our analyses. A wide range of variation was seen in these parameters: b-value ∼ 0.6–1.11, D e ∼ 0.97–1.64, and D t ∼ 0.13–0.93. The results showed decreases in all fractal parameters several months before the main shock. This decrease, which might have arisen due to clusters of events occurred between 2002–2003, was followed by a systematic increase, corresponding to the increased level of low-magnitude seismicity. It seems that changes in fractal parameters may be precursors of Baladeh-Kojour earthquake which was caused by seismic activation and quiescence. Furthermore, a positive correlation between b-value and D e was detected before the main shock (D e = 0.87 + 0.7b) and during aftershock sequences (D e = 2b ± 0.09), which was further on changed to a negative one (D e = 2.56–1.32b).

November 13, 1898 earthquake in Western Transbaikalia: a “white spot” in seismic history of East Siberia

The parametric catalogues of historical earthquakes in East Siberia contain large data gaps. Among these is a 15-year period in the late nineteenth century (1886–1901). This period was not covered by any of macroseismic catalogues known; neither acquisition nor systematization of macroseismic data was ever performed for that purpose. However, 15 years is a rather long period in which large seismic events may have occurred. The present paper deals with the previously unknown earthquake that occurred on November 13, 1898. The primary macroseismic data were taken from regional periodicals. On the strength of all the evidence obtained, the earthquake epicenter is localized in Western Transbaikalia, near the western end of the Malkhansky Range; the magnitude is estimated at M = 5.9. The information about the large earthquake of November 13, 1898 provides filling significant gaps in knowledge for seismicity in Western Transbaikalia and a better understanding of seismic potential of faults therein. The obtained results show that the periods of seismic quiescence in catalogues may be related to insufficient information on seismicity of Eastern Siberia in the historical past rather than to the absence of large earthquakes.

Cycles in mining seismicity

Stochastic models of self-organized criticality and intermittent criticality are used to describe the structure of seismic catalogs. The intermittent models introduce three phases of the seismic cycle: increase in seismic energy, seismic relaxation, and seismic quiescence after the final relaxation. In this paper, seismic mining catalogs from a deep copper mine are searched to find these three phases of the seismic cycle. In spite of the differences between the seismic records from earthquakes and the building of stresses in the mine, the cycles can be estimated in mining seismicity.