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1.
The objective of this paper is to quantify the use of past seismicity to forecast the locations of future large earthquakes and introduce optimization methods for the model parameters. To achieve this the binary forecast approach is used where the surface of the Earth is divided into l° × l° cells. The cumulative Benioff strain of m ≥ m c earthquakes that occurred during the training period, ΔT tr, is used to retrospectively forecast the locations of large target earthquakes with magnitudes ≥m T during the forecast period, ΔT for. The success of a forecast is measured in terms of hit rates (fraction of earthquakes forecast) and false alarm rates (fraction of alarms that do not forecast earthquakes). This binary forecast approach is quantified using a receiver operating characteristic diagram and an error diagram. An optimal forecast can be obtained by taking the maximum value of Pierce’s skill score.  相似文献   

2.
The May 12, 2008, Wenchuan M S 8.0/M w 7.9 earthquake occurred in the middle part of the north–south seismic zone in central west China, being one of the greatest thrust events on land in recent years. To explore whether there were some indications of the increase of strong earthquake probabilities before the Wenchuan earthquake, we conducted a retrospective forecast test applying the Pattern Informatics (PI) algorithm to the earthquakes in the Sichuan-Yunnan region since 1992. A regional earthquake catalogue complete to M L 3.0 from 01/01/1977 to 15/06/2008 was used. A 15-year long ‘sliding time window’ was used in the PI calculation, with ‘anomaly training time window’ and ‘forecast time window’ both set to 5 years. With a forecast target magnitude of M S 5.5, the ROC test shows that the PI forecast outperforms not only random guess but also the simple number-counting approach based on the clustering hypothesis of earthquakes (the RI forecast). ‘Hotspots’ can be seen in the region of the northern Longmenshan fault which is responsible for the Wenchuan earthquake. However, when considering bigger grid size and higher cutoff magnitude, such ‘hotspots’ disappear and there is very little indication of an impending great earthquake.  相似文献   

3.
—?An intriguing observation in Greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins, a piece of evidence for earthquake triggering due to postglacial rebound. Another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms. Sparse, low magnitude seismicity has made it difficult to determine focal mechanisms from Greenland earthquakes. On the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters, earlier investigators suggested that the earthquakes of Greenland are due to postglacial rebound. This interpretation is tested here by using more recent data. Broadband waveforms of teleseismic P waves from the August 10, 1993 (m b = 5.4) and October 14, 1998 (m b = 5.1) earthquakes have been inverted for moment tensors and source parameters. Both mechanisms indicate normal faulting with small strike-slip components: the 1993 event, strike = 348.9°, dip = 41.0°, rake =?56.3°, focal depth = 11?km, seismic moment = 1.03?×?1024 dyne-cm, and M w = 5.3; the 1998 event, strike = 61.6°, dip = 58.0°, rake =?95.5°, focal depth = 5?km, seismic moment = 5.72?×?1023 dyne-cm, and M w = 5.1. These and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension. The observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion. These local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults. Earthquake characteristics observed from Greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere.  相似文献   

4.
Utilizing chemical data derived from the various fault zone architectural components of the Clark strand of the San Jacinto fault, southern California, USA, we apply for the first time non-central principal component analysis to calculate a compositional linear trend within molar A–CN–K space. In this procedure A–CN–K are calculated as the molar proportions of Al2O3 (A), CaO* + Na2O (CN), and K2O (K) in the sum of molar Al2O3, Na2O, CaO*, and K2O. CaO* is the molar CaO after correction for apatite. We then derive translational invariant chemical alteration intensity factors, t, for each architectural component through orthogonal projection of analyzed samples onto the compositional linear trend. The chemical alteration intensity factor t determines the relative change in composition compared to the original state (i.e., the composition of the altered wall rocks). It is dependent on the degree of intensity to which the process or processes responsible for the change in composition of each architectural component has been active. These processes include shearing, fragmentation, fluid flow, and generation of frictional heat. Non-central principal component analysis indicates that principal component 1 explains 99.7 % of the spread of A–CN–K data about the calculated compositional linear trend (i.e., the variance). The significance level for the overall one-way analysis of variance (ANOVA) is 0.0001. Such a result indicates that at least one significant difference across the group of means of t values is different at the 95 % confidence level. Following completion of the overall one-way ANOVA, the difference in means t test indicated that the mean of the t values for the fault core are different than the means obtained from the transition and damage zones. In contrast, at the 95 % confidence level, the means of the t values for the transition and damage zones are not statistically distinguishable. The results of XRD work completed during this study revealed that the <2 µm fraction is composed primarily of illite/smectite with ~15 % illite in the damage zone, of illite/smectite with ~30 % illite in the transition zone, and of discreet illite with very minor smectite in the fault core. These changes parallel the increasing values of the chemical alteration intensity factors (i.e., t). Based on the above results, it is speculated that when fault zones are derived from tonalitic wall rocks at depths of ~400 ± 100 m, the onset of the illite/smectite to illite conversion will occur when t values exceed 0.20 ± 0.12, the average chemical alteration intensity factor calculated for the transition zone. Under such conditions during repeated rupturing events, frictional heat is produced and acidic fluids with elevated temperatures (≥ ~125 °C) are flushed through the fault core. Over time, the combination of shearing, fragmentation, and frictionally elevated temperatures eventually overcomes the kinetic barrier for the illite/smectite to illite transition. Such settings and processes are unique to fault zones, and as a result, they represent an underappreciated setting for the development of illite from illite/smectite. The success of non-central principal component analysis in this environment offers the first statistically rigorous methodology for establishing the existence of compositional linear trends in fault zones. This method also derives quantifiable alteration intensity factors that could potentially be used to compare the intensity of alteration at different segments of a fault, as well as offer a foundation to interpret the potential driving forces for said alteration and differences therein.  相似文献   

5.
The territory of Karelia (Baltic Shield) is virtually not represented in the global paleomagnetic database for the Lower Riphean time interval (1650—1350 Ma). As regards the paleointensity H an, the huge interval 1–2 Ga in length is represented in the global paleointensity database by only eight determinations concentrated in the interval 1–1.35 Ga. The paper presents results of paleomagnetic studies of volcanic and subvolcanic rocks composing the Early Riphean Salmi Formation, which outcrops in the valley of the lower Tulemaioki River in the northern coast area of Lake Ladoga. Results of the study indicate that, in the Early Riphean time, the East European craton was located in the tropical region of the Southern Hemisphere between 15° S and 40° S. The inferred value of H an is close to the lower boundary of the interval (1.36–11.56) × 1022 A m2, encompassing previously published intensity values of the paleofield 1–1.35 Ga; this supports the hypothesis on the existence of long intervals of a lower field in the period in question [Maquoin et al., 2003].  相似文献   

6.
The Comprehensive Nuclear-Test-Ban Treaty (CTBT), a global ban on nuclear explosions, is currently in a ratification phase. Under the CTBT, an International Monitoring System (IMS) of seismic, hydroacoustic, infrasonic and radionuclide sensors is operational, and the data from the IMS is analysed by the International Data Centre (IDC). The IDC provides CTBT signatories basic seismic event parameters and a screening analysis indicating whether an event exhibits explosion characteristics (for example, shallow depth). An important component of the screening analysis is a statistical test of the null hypothesis H 0: explosion characteristics using empirical measurements of seismic energy (magnitudes). The established magnitude used for event size is the body-wave magnitude (denoted m b) computed from the initial segment of a seismic waveform. IDC screening analysis is applied to events with m b greater than 3.5. The Rayleigh wave magnitude (denoted M S) is a measure of later arriving surface wave energy. Magnitudes are measurements of seismic energy that include adjustments (physical correction model) for path and distance effects between event and station. Relative to m b, earthquakes generally have a larger M S magnitude than explosions. This article proposes a hypothesis test (screening analysis) using M S and m b that expressly accounts for physical correction model inadequacy in the standard error of the test statistic. With this hypothesis test formulation, the 2009 Democratic Peoples Republic of Korea announced nuclear weapon test fails to reject the null hypothesis H 0: explosion characteristics.  相似文献   

7.
We present the main seismological results of our study of the Campania-Lucania earthquake of 23 November 1980. A complete set of far field and local data has been analysed. From long-period body waves data we determine the fault plane solution (φ1 = 140°,δ1 = 60°,φ2 = 75°,δ2 = 54°), a depth of 15 km and calculate a seismic moment of 6 × 1025 dyne cm and a source duration of 6 s. From data of a local network deployed immediately after the event we determine aftershock locations: they are aligned in a direction NW-SE that fit extremely well with the focal solution determined above. We can choose as fault plane the plane striking 140° and dipping at 60° and the event is a normal event with a large component of left-lateral strike slip. The source area evaluated from this aftershock distribution 14 km × 40 km is quite suitable for an earthquake of a seismic moment of 6 × 1025 dyne cm.  相似文献   

8.
Atmospheric particulate matter (PM) is one of the pollutants that may have a significant impact on human health. Data collected over 7 years from the air quality monitoring station at the LD-III steelworks, belonging to the Arcelor-Mittal Steel Company, located in the metropolitan area of Avilés (Principality of Asturias, Northern Spain), is analyzed using four different mathematical models: vector autoregressive moving-average, autoregressive integrated moving-average (ARIMA), multilayer perceptron neural networks and support vector machines with regression. Measured monthly, the average concentration of pollutants (SO2, NO and NO2) and PM10 (particles with a diameter less than ?10 μm) is used as input to forecast the monthly average concentration of PM10 from one to 7 months ahead. Simulations showed that the ARIMA model performs better than the other models when forecasting 1 month ahead, while in the forecast from one to 9 months ahead the best performance is given by the support vector regression.  相似文献   

9.
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been measured in twenty Antarctic meteorites by neutron activation analysis.36Cl (t1/2 = 3.0 × 105years) has been measured in fourteen of these objects by tandem accelerator mass spectrometry. Cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases.14C (t1/2 = 5740years) and26Al (t1/2 = 7.2 × 105years) data. The terrestrial ages range from 3 × 104 to 5 × 105 years. Many of the L3 Allan Hills chrondrites seem to be a single fall based on these results. In addition,10Be (t1/2 = 1.6 × 106years) and36Cl have been measured in six Antarctic ice samples. The first measurements of10Be/36Cl ratios in the ice core samples demonstrate a new dating method for ice.  相似文献   

10.
以日本局部地区（32.0°N—46.0°N,136.0°E—148.0°E）为研究区域,应用图像信息（PI）方法,获得了不同计算参数模型下包含2011年3月11日日本东北MW9.0地震的多组预测窗热点图像。以0.5°×0.5°和1.0°×1.0°的网格尺度和5—10年预测窗长为主要参数变量,并以R值和受试者工作特征（ROC）方法检验不同参数模型下PI方法的预测效能。结果表明,多组参数模型下MW9.0地震所在预测窗内,其震中所在网格及其摩尔邻近网格均曾出现热点图像,表明PI方法可对日本东北MW9.0地震作出预测。综合R值评分和ROC检验分析可知,网格尺度相对较大、预测窗长相对较长的模型,其预测效果更好。   相似文献   

11.
We estimated the network-averaged mantle attenuation t*(total) of 0.5 s beneath the North Korea test site (NKTS) by use of P-wave spectra and normalized spectral stacks from the 25 May 2009 declared nuclear test (mb 4.5; IDC). This value was checked using P-waves from seven deep (580–600 km) earthquakes (4.8 < M w < 5.5) in the Jilin-Heilongjiang, China region that borders with Russia and North Korea. These earthquakes are 200–300 km from the NKTS, within 200 km of the Global Seismic Network seismic station in Mudanjiang, China (MDJ) and the International Monitoring System primary arrays at Ussuriysk, Russia (USRK) and Wonju, Republic of Korea (KSRS). With the deep earthquakes, we split the t*(total) ray path into two segments: a t*(u), that represents the attenuation of the up-going ray from the deep hypocenters to the local-regional receivers, and t*(d), that represents the attenuation along the down-going ray to teleseismic receivers. The sum of t*(u) and t*(d) should be equal to t*(total), because they both share coincident ray paths. We estimated the upper-mantle attenuation t*(u) of 0.1 s at stations MDJ, USRK, and KSRS from individual and stacks of normalized P-wave spectra. We then estimated the average lower-mantle attenuation t*(d) of 0.4 s using stacked teleseismic P-wave spectra. We finally estimated a network average t*(total) of 0.5 s from the stacked teleseismic P-wave spectra from the 2009 nuclear test, which confirms the equality with the sum of t*(u) and t*(d). We included constraints on seismic moment, depth, and radiation pattern by using results from a moment tensor analysis and corner frequencies from modeling of P-wave spectra recorded at local distances. We also avoided finite-faulting effects by excluding earthquakes with complex source time functions. We assumed ω2 source models for earthquakes and explosions. The mantle attenuation beneath the NKTS is clearly different when compared with the network-averaged t* of 0.75 s for the western US and is similar to values of approximately 0.5 s for the Semipalatinsk test site within the 0.5–2 Hz range.  相似文献   

12.
Line-of-sight magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO) and by the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) for 14 emerging ARs were used to study the derivative of the total unsigned flux–the flux emergence rate, R(t). We found that the emergence regime is not universal: each AR displays a unique emergence process. Nevertheless, two types of the emergence process can be identified. First type is a “regular” emergence with quasi-constant behavior of R(t) during a 1–3 day emergence interval with a rather low magnitude of the flux derivative, Rmax = (0.57 ± 0.22) × 1022 Mx day–1. The second type can be described as “accelerated” emergence with a long interval (>1 day) of the rapidly increasing flux derivative R(t) that result in a rather high magnitude of Rmax= (0.92 ± 0.29) × 1022 Mx day–1, which later changes to a very short (about a one third of day) interval of R(t) = const followed by a monotonous decrease of R(t). The first type events might be associated with emergence of a flux tube with a constant amount of flux that rises through the photosphere with a quasi-constant speed. Such events can be explained by the traditional largescale solar dynamo generating the toroidal flux deep in the convective zone. The second-type events can be interpreted as a signature of sub-surface turbulent dynamo action that generates additional magnetic flux (via turbulent motions) as the magnetic structure makes its way up to the solar surface.  相似文献   

13.
The 2017 Guptkashi earthquake occurred in a segment of the Himalayan arc with high potential for a strong earthquake in the near future. In this context, a careful analysis of the earthquake is important as it may shed light on source and ground motion characteristics during future earthquakes. Using the earthquake recording on a single broadband strong-motion seismograph installed at the epicenter, we estimate the earthquake’s location (30.546° N, 79.063° E), depth (H?=?19 km), the seismic moment (M0?=?1.12×1017 Nm, M w 5.3), the focal mechanism (φ?=?280°, δ?=?14°, λ?=?84°), the source radius (a?=?1.3 km), and the static stress drop (Δσ s ~22 MPa). The event occurred just above the Main Himalayan Thrust. S-wave spectra of the earthquake at hard sites in the arc are well approximated (assuming ω?2 source model) by attenuation parameters Q(f)?=?500f0.9, κ?=?0.04 s, and fmax?=?infinite, and a stress drop of Δσ?=?70 MPa. Observed and computed peak ground motions, using stochastic method along with parameters inferred from spectral analysis, agree well with each other. These attenuation parameters are also reasonable for the observed spectra and/or peak ground motion parameters in the arc at distances ≤?200 km during five other earthquakes in the region (4.6?≤?M w ?≤?6.9). The estimated stress drop of the six events ranges from 20 to 120 MPa. Our analysis suggests that attenuation parameters given above may be used for ground motion estimation at hard sites in the Himalayan arc via the stochastic method.  相似文献   

14.
Cosmic-ray-produced53Mn (t1/2 = 3.7 × 106years) has been determined by neutron activation in nine Allan Hills-77 meteorites. Additionally,36Cl (1/2 = 3.0 × 105years) has been measured in seven of these objects using tandem accelerator mass spectrometry. These results, along with14C (t1/2 = 5740years) and26Al (7.2 × 105 years) concentrations determined elsewhere, yield terrestrial ages ranging from 0.1 × 105 to 7 × 105 years. Weathering was not found to result in53Mn loss.  相似文献   

15.
Repeat times of strong shallow mainshocks have been determined by the use of instrumental and historical data for 68 seismogenic sources in the Aegean and surrounding area (34°N–43°N, 18°E–30°E). For 49 of these sources at least two interevent times (three mainshocks) are available for each source. By using the repeat times for these 49 sources the following relation has been determined: $$\log T_t = 0.36M_{\min } + 0.35M_p + a$$ whereT t is the repeat time, measured in years,M p the surface wave magnitude of the preceding mainshock,M min the magnitude of the smallest earthquake considered and “a” parameter which varies from source to source. A multilinear correlation coefficient equal to 0.89 was determined for this relation. By using the same repeat times for the 49 seismogenic sources, the following relation has been determined between the magnitude,M f , of the following mainshock andM min andM p . $$M_f = 0.95M_{\min } - 0.49M_p + m$$ wherem is a constant which varies from source to source. A multilinear correlation coefficient equal to 0.80 was found for this relation. The model expressed by these two relations is represented by a scheme of a time variation of stress under constant tectonic loading. In this scheme, the maximum stress values during the different seismic cycles fluctuate around a value, τ1, in a relatively narrow stress interval, expressing the high correlation coefficient of the relation between LogT andM p . On the contrary, the minimum stress values fluctuate around a value, τ2, in a much broader stress interval. However, each of these minimum stress values becomes lower or higher than τ2 if the previous one is higher or lower than τ2, respectively, expressing the negative correlation betweenM f andM p .  相似文献   

16.
The Precambrian basement of the British region south of the Caledonian orogenic belt is only observed in a few small inliers; this paper reports a detailed paleomagnetic study of four of these inliers. The Stanner-Hanter amphibolitised gabbro-dolerite complex of uncertain age yields a mean direction of magnetisation D = 282°, I = 51° (15 sites,α95 = 11.4°) after AF and thermal cleaning. Uriconian lavas and tuffs (～700-600 m.y.) of the Pontesford and Wrekin inliers require both thermal and AF cleaning for complete analysis of NRM. The former region (Western Uriconian) yields a mean of D = 136°, I = ?25° (6 sites,α95 = 15.3°) and the latter region (Eastern Uriconian) a mean of D = 78°, I = 17° (9 sites, α95 = 12.8°); the Eastern Uriconian shows a marked improvement in precision after a two-stage fold test, and the palaeomagnetic data suggest that some apparent polar movement took place between eruption of the two sequences. The Uriconian rocks in both areas were intruded by dolerites which yield a mean direction of magnetisation D = 72°, I = 54° (11 sites,α95 = 13.2°).The collective data give palaeomagnetic poles related to Upper Proterozoic metamorphic episodes (Stanner-Hanter Complex and Rushton Schist) which are in close agreement with earlier studies of the Malvernian metamorphic rocks, and to the late Precambrian Uriconian volcanic/hypabyssal igneous episode. All of these magnetisations are probably confined to the interval 700-600 m.y., and are indicative of appreciable polar movement during this interval. The palaeomagnetic poles define an apparent polar wander path for this crustal block between Late Precambrian and Lower Cambrian times and show that cratonic Britain south of the Caledonian suture is unrelated to the Baltic Shield.  相似文献   

17.
Variability of the Earth’s structure makes a first-order impact on attenuation measurements which often does not receive adequate attention. Geometrical spreading (GS) can be used as a simple measure of the effects of such structure. The traditional simplified GS compensation is insufficiently accurate for attenuation measurements, and the residual GS appears as biases in both Q 0 and η parameters in the frequency-dependent attenuation law Q(f) = Q 0 f η . A new interpretation approach bypassing Q(f) and using the attenuation coefficient χ(f) = γ + πf/Q e(f) resolves this problem by directly measuring the residual GS, denoted γ, and effective attenuation, Q e. The approach is illustrated by re-interpreting several published datasets, including nuclear-explosion and local-earthquake codas, Pn, and synthetic 50–300-s surface waves. Some of these examples were key to establishing the Q(f) concept. In all examples considered, χ(f) shows a linear dependence on the frequency, γ ≠ 0, and Q e can be considered frequency-independent. Short-period crustal body waves are characterized by positive γ SP values of (0.6–2.0) × 10?2 s?1 interpreted as related to the downward upper-crustal reflectivity. Long-period surface waves show negative γ LP ≈ ?1.9 × 10?5 s?1, which could be caused by insufficient modeling accuracy at long periods. The above γ values also provide a simple explanation for the absorption band observed within the Earth. The band is interpreted as apparent and formed by levels of Q e ≈ 1,100 within the crust decreasing to Q e ≈ 120 within the uppermost mantle, with frequencies of its flanks corresponding to γ LP and γ SP. Therefore, the observed absorption band could be purely geometrical in nature, and relaxation or scattering models may not be necessary for explaining the observed apparent Q(f). Linearity of the attenuation coefficient suggests that at all periods, the attenuation of both Rayleigh and Love waves should be principally accumulated at the sub-crustal depths (~38–100 km).  相似文献   

18.
Using bathymetry and altimetric gravity anomalies, a 1° 9 1° lithospheric effective elastic thickness(Te) model over the Louisville Ridge and its adjacent regions is calculated using the moving window admittance technique. For comparison, three bathymetry models are used: general bathymetric charts of the oceans, SIO V15.1,and BAT_VGG. The results show that BAT_VGG is more suitable for calculating T e than the other two models. T e along the Louisville Ridge was re-evaluated. The southeast of the ridge has a medium Te of 10–20 km, while Te increases dramatically seaward of the Tonga-Kermadec trench as a result of the collision of the Pacific and IndoAustralian plates.  相似文献   

19.
Temporal distribution of earthquakes with M w > 6 in the Dasht-e-Bayaz region, eastern Iran has been investigated using time-dependent models. Based on these types of models, it is assumed that the times between consecutive large earthquakes follow a certain statistical distribution. For this purpose, four time-dependent inter-event distributions including the Weibull, Gamma, Lognormal, and the Brownian Passage Time (BPT) are used in this study and the associated parameters are estimated using the method of maximum likelihood estimation. The suitable distribution is selected based on logarithm likelihood function and Bayesian Information Criterion. The probability of the occurrence of the next large earthquake during a specified interval of time was calculated for each model. Then, the concept of conditional probability has been applied to forecast the next major (M w > 6) earthquake in the site of our interest. The emphasis is on statistical methods which attempt to quantify the probability of an earthquake occurring within a specified time, space, and magnitude windows. According to obtained results, the probability of occurrence of an earthquake with M w > 6 in the near future is significantly high.  相似文献   

20.
The natural remanent magnetization of 22 out of a total of 31 oriented cores from the layered series of the Skaergaard gabbroic intrusion (age: 55 m.y.) in East Greenland shows good stability in thermal and AF testing. The average direction of 22 AF and 9 thermally treated specimens isD = 170°,I = ?59°,α95 = 4.2 before correction for tilt. The mean directions after rotation around strike to horizontal and after rotation to original attitudes suggested by others yields poorer population statistics. It is therefore concluded that flexuring took place between solidification and acquisition of remanent magnetization, a range in temperature of about 500°C which may represent an interval of somewhat less than 250,000 years. No evidence for secular variation is observed which may also suggest slow cooling through the blocking temperature range. The polarity is reversed and the pole position without “tilt correction” is 165°E, 61°N,dm = 6.2,dp = 4.6, which is similar to pole positions reported by others for the overlying slightly older basalt.  相似文献   

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