The study applies the Integrated Tsunami Intensity Scale (ITIS2012) criteria to map the tsunami intensities distribution in the broader Ishinomaki area, for the 9 Mw March 11, 2011 event offshore Tohoku, Japan. Based on reports, satellite imagery and published information, impact data was mapped, intensity values were assigned and thematic impact maps (layers) were created for each of the ITIS2012 six criteria categories. Most of the criteria result in a mosaic of intensities, which is in many cases due to lack of data, depending on the land use. Two methodologies were used to produce the final map. A land-use-based weighted overlay was applied integrating the six layers, resulting in a final map that rather shows damage tsunami assessment on Ishinomaki area. The second final map was produced using the maximum intensity grade throughout the six layers for each pixel. This map showed an excellent zoning filling in any gaps due to information lack in some layers and areas, with maximum intensity data from the others, highlighting the ITIS2012 criteria complementarity and is the tsunami intensity map of the study area.
Decelerating generation of intermediate magnitude earthquakes (preshocks) in a narrow region (seismogenic region) and accelerating generation of relatively larger such earthquakes in a broader region (critical region) has been proposed as an appropriate model for intermediate-term earthquake prediction. We examined the seismic activity which preceded the M w =7.7 (October 28, 2012) thrust event that occurred off the west coast of Haida Gwaii, Canada (formerly the Queen Charlotte islands), by applying the decelerating-accelerating seismic strain model. We found that this mainshock was preceded by a pronounced accelerating seismic sequence with the time to the mainshock, as well as by an equally easily identifiable decelerating seismic sequence. Both precursory seismic sequences occurred in different space, time and magnitude windows. The behavior of previous mainshocks that occurred close to the 2012 earthquake was also examined by the time and magnitude predictable regional model. An attempt was also made to identify such seismic strain patterns, which may also be related to the generation of strong mainshocks along the western coast of Canada.
We consider the dynamics of different parameters in the boundary layer of atmosphere and low level cloud structure around the time of three recent moderate and strong earthquakes: Virginia M 5.8 earthquake on August 23 2011 in USA, Van M 7.1 earthquake on October 23 2011 in Turkey, and Northwestern Iran M 6.4 earthquake on August 11, 2012, Iran. Using as indicators the water vapor chemical potential correction value, aerosol optical thickness, and linear cloud structures appearance we discovered their coherence in space and time within the time interval 3-5 days before the seismic shock. Obtained results are interpreted as synergetic result of the lithosphere-atmosphere-ionosphere coupling process.
In this paper we present results of a comparison between ultra low frequency (ULF) electromagnetic (EM) radiation, recorded by an electric field instrument onboard the satellite detection of electromagnetic emissions transmitted from earthquake regions in the topside ionosphere, and the seismicity of regions with high and low seismic activity. In particular, we evaluated the energy variations of the ULF Ezelectric field component during a period of four years (2006-2009), in order to examine the possible relation of ULF EM radiation with seismogenic regions located in Central America, Indonesia, the Eastern Mediterranean Basin and Greece. As a tool for evaluating the ULF Ez energy variations we used singular spectrum analysis techniques. The results of our analysis clearly show a significant increase of the ULF EM energy emitted from regions of highest seismic activity at the boundaries tectonic plates. Furthermore, we found that higher electromagnetic radiation was detected in a region above the northern- western Greek Arc (R1) than above the adjacent region including Athens and its urban area. We interpret these results of the present study as suggesting that: i) the seismogenic regions at the boundary of tectonic plates radiate ULF EM emissions observed by satellites in the topside ionosphere; and ii) that this EM radiation is not only related with the occurrence time of great (M≥5) earthquakes, but it is often present in intermediate times and it appears as a quasi-permanent phenomenon.
On 26.1.2014 and 3.2.2014 two strong earthquakes of Mw6.0 and Mw5.9 ruptured the western Cephalonia Isl., Ionian Sea (Greece), at the SSW-wards continuation of the Lefkada segment of the Cephalonia Transform Fault Zone (CTFZ), causing considerable damage and a variety of ground failures. High-precision relocation of the aftershocks implies that the seismogenic layer was of 35 km in length (L) striking NNE-SSW, of 10 km maximum in width and 15 km in thickness. Two aftershock spatial clusters were revealed at north (L1~10 km) and at south (L2~25 km). However, no time correlation was found between the two clusters and the two strong earthquakes. Fitting the temporal evolution of aftershocks to the Omori-law showed slow aftershock decay. Fault plane solutions produced by moment tensor inversions indicated that the strong earthquakes as well as a plenty of aftershocks (Mw≥4.0) were associated with dextral strikeslip faulting with some thrust component and preferred fault planes striking about NNE-SSW. Average fault plane parameters obtained for the three largest events are: strike 21(±2)0, dip 65.5(±3)0, slip 173(±3)0. Broadband P-wave teleseismic records were inverted for understanding the rupture histories. It was found that the earthquake of 26.1.2014 had a complex source time function with c. 62 cm maximum slip, source duration of ~12 s and downwards rupture. Most of the slip was concentrated on a 13x9 km fault rupture. The earthquake of 3.2.2014 had a relatively simple source time function related with one big patch of slip with maximum slip c. 45 cm, with 10 s source duration. The rupture was directed upwards which along with the shallow focus (~5 km) and the simple source time function may explain the significantly larger (0.77 g) PGA recorded with the second earthquake with respect to the one recorded (0.56 g) with the first earthquake. Most of the slip was concentrated on a 12x6 km fault rupture. Maximum seismic intensity (Im) of level VII and VIII to VIII+ was felt in Lixouri town and the nearby villages from the first and the second earthquake, respectively. The rupture histories and the increased building vulnerability after the damage caused by the first shock may account for the larger Im caused by the second shock. However, the ground failures area of the second earthquake was nearly half of that of the first earthquake, which is consistent with the faster attenuation of ground acceleration away from the meizoseismal area caused by the second earthquake with respect to the first one. From that the 2014 earthquakes ruptured on land western Cephalonia we suggested to revise the CTFZ geometry in the sense that the Lefkada CTFZ segment does not terminates offshore NW Cephalonia but extends towards SSW in western Cephalonia.
Micro-cracking in the earthquake preparation zone is accompanied by the generation of acoustic emission (AE). Even low-intensity AE can essentially modify the underground fluid dynamics owing to the influence of high-frequency acoustic field on filtration process. Laboratory experiments show that acoustic impact on pour sample destroys a film with bounded water and results in a steep increase of its permeability up to 2 orders of magnitude. Impulsive acoustic fields also decrease the effective viscosity of the fluid. The occurrence in the crust under pressure of a region with distinct hydrodynamic and electrokinetic parameters will result in an appearance of anomalous telluric and magnetic fields on the surface above. This effect is estimated analytically using a simple model with an ellipticshaped inhomogeneity. The suggested hypothesis about possible coupling between AE and geoelectrical anomalies needs observational verification.
On 26 December 2004 and 28 March 2005 occurred two of the largest earthquakes of the last 40 years between the Indo-Australian and the southeastern Eurasian plates, with moment magnitudes Mw=9.1 and Mw= 8.6 respectively. Complete data (mb > 4.2) of the post-1993 time interval (Fig. 1) have been used to apply Poisson Hidden Markov Models (PHMM in identifying temporal patterns in the time series of the two main shocks. Each time series consists of earthquake counts, in given and constant time units, in the regions determined by the aftershock zones of the two main shocks. In PHMM each count is generated by one of m Poisson processes, that are called states. The series of states is unobserved and is, in fact a Markov chain. The model incorporates a varying seismicity rate; it assigns a different rate to each state, and detects the changes of the rate over time. In PHMM, unobserved factors related to the local properties of the region, affect the earthquake occurrence rate. Estimation and interpretation of the unobserved sequence of states that underlie the data contribute to a better understanding of the geophysical processes that take place in the region. We applied PHMM to the time series of earthquakes preceding the two main shocks, and we estimated the unobserved sequences of states that underlie the data. The results showed that the region of the 26 December 2004 earthquake was in state of low seismicity during about 400 days before the earthquake occurrence. On the contrary, in the region of the 28 March 2005 earthquake a transition from a state of low seismicity to a state of high seismicity was observed immediately after the occurrence of the big earthquake of 26 December 2004.
The temporal variation of seismicity, based on the retrospective analyses of three seismic parameters <em>i.e.</em>, number of earthquakes, bvalue and energy released, have shown significant changes. Their remarkable relation with strong earthquakes occurrence was formulated as a qualitative character precursory seismicity pattern, which were interpreted in terms of a strong earthquakes occurrence preparation phases. The main characteristic of this pattern is that permits the identification of two period of low and high probability for an earthquake occurrence, suggesting its utility in the current seismic hazard assessment, by the continuous monitoring of the temporal variation of the seismic parameters in a given area. This paper investigates the qualitative and quantitative characteristics of the proposed precursory seismicity pattern, before al strong earthquakes occurrence in Greece the time period 2000-2008.
Satellite data of thermal images revealed the existence of thermal fields, connected with big linear structures and systems of crust faults. The measuring height of outgoing longwave radiation is located to the range of jet stream. This work describes a possible link between strong earthquakes and jet streams in two regions. The front or tail ends of jet groups maintain their position for 6 or more hours in the vicinity of epicenters of strong (M>6.0) earthquakes in 2006-2010. The probability of observing a stationary jet stream behavior is estimated in 93.6% of the cases on one sixhour map and in 26.7% of cases - on two adjacent maps. The median of distribution of distances between epicenters and the relevant positions of jet stream corresponds to 36.5 km. Estimates of cumulative probability of realization of prediction were 24.2% for 10 days, 48.4% for 20 days, 66.1% for 30 days, 87.1% for 40 days, 93.5% for 50 days and 100% during 70 days. The observed precursory effects are of considerable interest for possible use for real short-term prediction of earthquakes.
A total of 93 well-defined PKS, 54 SKKS, and 126 SKS shear-wave splitting parameters are determined at 25 broadband seismic stations in an approximately 1000 by 1000 km2 area centered at the New Madrid seismic zone (NMSZ) in order to test the existence of two anisotropic layers and to map the direction and strength of mantle fabrics. The individual splitting parameters suggest a significant and systematic spatial and azimuthal variation in the splitting parameters. The azimuthal variations at most stations can be explained as the results of present SW ward asthenospheric flow and NNE trending lithospheric fabrics formed during past orogenic events. In the NMSZ, rift-parallel fast directions (potentially related to a long-rift flow) and rift-orthogonal fast directions from small-scale mantle convection are not observed. In addition, reduction in splitting times as a result of vertical asthenospheric flow is not observed.
The Mesoproterozoic Midcontinent rift (MCR) in the central US is an approximately 2000 km long, 100 km wide structure from Kansas to Michigan. During the 20-40 million years of rifting, a thick (up to 20 km) layer of basaltic lava was deposited in the rift valleys. Quantifying the effects of the rifting and associated volcanic eruptions on the structure and composition of the crust and mantle beneath the MCR is important for the understanding of the evolution of continental lithosphere. In this study we measure the crustal thickness (H), and the sharpness of the Moho (R) at about 24 portable and permanent stations in Iowa, Kansas, and South Dakota by stacking Pto- S converted waves (PmS) and their multiples (PPmS and PSmS). Under the assumption that the crustal mean velocity in the study area is the same as the IASP91 earth model, we find a significantly thickened crust beneath the MCR of about 53 km. The crustal V p /V s ratios increases from about 1.80 off rift to as large as 1.95 within the rift, which corresponds to an increase of Poisson’s ratio from 0.28 to 0.32, suggesting a more mafic crust beneath the MCR. The R measurements are spatially variable and are relatively small in the vicinity of the MCR, indicating the disturbance of the original sharp Moho by the rifting and magmatic intrusion and volcanic eruption.
Before an earthquake occurs, microseismic noise in high frequency (HF) range, i.e. 2-25 Hz, is being generated during preparation process. These signals change the microseismic noise and, consequently, the spectrum of microseismic noise. Time variation of spectra recorded at the same seismological station could imply the change of the state of noise source. We propose the image moment analysis approach to objectively compare microseismic noise spectra. The result could be used for earthquake precursor identification. Expected spectra change is in HF range, so the analysis has been limited to the shallow tectonic earthquakes with epicenters close, up to 15 km, the seismological stations. The method has been tested post festum using four earthquakes in Dinarides which satisfied condition for epicentral distance. The spectra were calculated for noise recorded in time intervals of 10 days before and 6 to 10 days after the earthquakes. Affine moment invariants were calculated for noise spectra which were treated as the input objects. Spectra of the first five days in the series were referent spectra. The classification parameters were Euclidean distances between referent spectra and the spectra for all days in the series, including referent ones. The results have shown that the spectra of the microseismic noise become noticeably different than the other spectra in time intervals one or two days before an earthquake.
The new European project Near-field Tsunami Early Warning and Emergency Planning in the Mediterranean Sea (NEARTOWARN) faces the need to develop operational tsunami early warning systems in near-field (local) conditions where the travel time of the first tsunami wave is very short, that is less than 30 min, which is a typical case in the North East Atlantic and the Mediterranean Sea region but also elsewhere around the globe. The operational condition that should be fulfilled is that the time of tsunami detection, plus the time of warning transmitting, plus the time of evacuation should not exceed the travel time of the first tsunami wave from its source to the closest evacuation zone. To this goal the time to detect of the causative earthquake should be compressed at the very minimum. In this context the core of the proposed system is a network of seismic early warning devices, which activate and send alert in a few seconds after the generation of a near-field earthquake, when a seismic ground motion exceeding a prescribed threshold is detected. Then civil protection mobilizes to manage the earthquake crisis but also to detect and manage a possible tsunami through a geographical risk management system. For the tsunami detection the system is supported by tide-gauges of radar type, a database of presimulated tsunami scenarios, and a local tsunami decision matrix. The island of Rhodes in the eastern termination of the Hellenic Arc and Trench has been selected for a pilot and operational development of the local tsunami warning system given that the island is a highly popular tourist destination, historically it was hit by large tsunamigenic earthquakes and was recently the master test-site for the pan-European FP6 tsunami research project Tsunami Risk ANd Strategies For the European Region (TRANSFER).
It is a widely shared opinion that not only secondary earthquakes (aftershocks) but also main earthquakes tend to occur in time-space clusters. The importance of this assumption requires the application of statistical tools to objectively evaluate its coherence with the reality at different scales of size-space-time. Global tests allow us to select the data sets with significant space-time clustering in order to perform more in-depth analyses to detect cluster locations. According to different fixed magnitude thresholds, we perform two global statistical tests, the Knox test and the Jacquez test, based on the space-time distance between pairs of earthquakes under the null hypothesis of uniform distribution in time and space, and evaluate the significance of the possible clusters. We analyze subsets of historical Italian earthquakes drawn from the Parametric Catalog of Italian Earthquakes (CPTI04) with magnitude thresholds 4.5, 5.3 and 6.0, associated with the composite seismogenic sources of the Database of Individual Seismogenic Sources. Each subset is related to one of the eight tectonically homogeneous macroregions in which the Italian territory has been divided. Significant space-time clustering is found for all sets with a magnitude threshold of 4.5. This tendency decreases drastically or disappears when the cut off rises to 5.3, with the exception of two macroregions located in the Eastern Alps and the Calabrian Arc, respectively, where evidence of space-time interaction may refer to stress transfer among consecutive or adjacent faults. The link between clustering effect and tectonic behavior could guide the choice of different stochastic point processes to model the seismic activity.
The Collaboratory for the Study of Earthquake Predictability (CSEP) is a global project aimed at testing earthquake forecast models in a fair environment. Various metrics are currently used to evaluate the submitted forecasts. However, the CSEP still lacks easily understandable metrics with which to rank the universal performance of the forecast models. In this research, we modify a well-known and respected metric from another statistical field, bioinformatics, to make it suitable for evaluating earthquake forecasts, such as those submitted to the CSEP initiative. The metric, originally called a gene-set enrichment score, is based on a Kolmogorov-Smirnov statistic. Our modified metric assesses if, over a certain time period, the forecast values at locations where earthquakes have occurred are significantly increased compared to the values for all locations where earthquakes did not occur. Permutation testing allows for a significance value to be placed upon the score. Unlike the metrics currently employed by the CSEP, the score places no assumption on the distribution of earthquake occurrence nor requires an arbitrary reference forecast. In this research, we apply the modified metric to simulated data and real forecast data to show it is a powerful and robust technique, capable of ranking competing earthquake forecasts.
The Regional Earthquake Likelihood Models (RELM) test was the first competitive comparison of prospective earthquake forecasts. The test was carried out over 5 years from 1 January 2006 to 31 December 2010 over a region that included all of California. The test area was divided into 7682 0.1°x0.1° spatial cells. Each submitted forecast gave the predicted numbers of earthquakes Nemi larger than M=4.95 in 0.1 magnitude bins for each cell. In this paper we present a method that separates the forecast of the number of test earthquakes from the forecast of their locations. We first obtain the number Nem of forecast earthquakes in magnitude bin m. We then determine the conditional probability λemi=Nemi/Nem that an earthquake in magnitude bin m will occur in cell i. The summation of λemi over all 7682 cells is unity. A random (no skill) forecast gives equal values of λemi for all spatial cells and magnitude bins. The skill of a forecast, in terms of the location of the earthquakes, is measured by the success in assigning large values of λemi to the cells in which earthquakes occur and low values of λemi to the cells where earthquakes do not occur. Thirty-one test earthquakes occurred in 27 different combinations of spatial cells i and magnitude bins m, we had the highest value of λemi for that mi cell. We evaluate the performance of eleven submitted forecasts in two ways. First, we determine the number of mi cells for which the forecast λemi was the largest, the best forecast is the one with the highest number. Second, we determine the mean value of λemi for the 27 mi cells for each forecast. The best forecast has the highest mean value of λemi. The success of a forecast during the test period is dependent on the allocation of the probabilities λemi between the mi cells, since the sum over the mi cells is unity. We illustrate the forecast distributions of λemi and discuss their differences. We conclude that the RELM test was successful in illustrating the choices required when a forecast of the location of a future earthquake is made.
This study examines the global earthquake detection capability of the Global Centroid Moment Tensor (GCMT) catalogue during the periods immediately following large earthquakes, including intermediate-depth (70 ≤ depth < 300 km) and deep (300 km ≤ depth) events. We have already shown that the detection capability beyond an aftershock zone degrades remarkably and that this condition persists for several hours after the occurrence of large shallow (depth < 70 km) earthquakes. Because an intermediate-depth or deep earthquake occasionally generates seismic waves with significant amplitudes, it is necessary to investigate the change in the detection capability caused by such events. To this end, from the GCMT catalogue, we constructed the time sequences of the earthquakes that occurred immediately after the large earthquakes, and stacked these time sequences. To these stacked sequences, we then applied a statistical model representing the magnitude-frequency distribution of all observed earthquakes. This model has a parameter that characterizes the detection capability, and the temporal variation of the parameter is estimated by means of a Bayesian approach with a piecewise linear function. Consequently, we find that the global detection capability is lower after the occurrence of shallow earthquakes with magnitudes ≥ 5.45, intermediate-depth earthquakes with magnitudes ≥ 5.95, and deep earthquakes with magnitudes ≥ 6.95.
Tests of aftershock forecast have to consider the temporal distribution of aftershocks, which differ from mainshocks. This paper uses as an example the 2008 Wenchuan aftershock sequence and the load-unload response ratio forecast of aftershocks. We discuss a simplified test scheme using the Ogata-transformed time to make the transformed aftershock sequence homogenously random. While an example was taken using the Molchan error diagram, other testing schemes are also valid for the transformed aftershock sequence.
Based on the ETAS (epidemic-type aftershock sequence) model, which is used for describing the features of short-term clustering of earthquake occurrence, this paper presents some theories and techniques related to evaluating the probability distribution of the maximum magnitude in a given space-time window, where the Gutenberg-Richter law for earthquake magnitude distribution cannot be directly applied. It is seen that the distribution of the maximum magnitude in a given space-time volume is determined in the longterm by the background seismicity rate and the magnitude distribution of the largest events in each earthquake cluster. The techniques introduced were applied to the seismicity in the Japan region in the period from 1926 to 2009. It was found that the regions most likely to have big earthquakes are along the Tohoku (northeastern Japan) Arc and the Kuril Arc, both with much higher probabilities than the offshore Nankai and Tokai regions.
The Every Earthquake a Precursor According to Scale (EEPAS) long-range earthquake forecasting model has been shown to be informative in several seismically active regions, including New Zealand, California and Japan. In previous applications of the model, the tectonic setting of earthquakes has been ignored. Here we distinguish crustal, plate interface, and slab earthquakes and apply the model to earthquakes with magnitude M≥4 in the Japan region from 1926 onwards. The target magnitude range is M≥ 6; the fitting period is 1966-1995; and the testing period is 1996-2005. In forecasting major slab earthquakes, it is optimal to use only slab and interface events as precursors. In forecasting major interface events, it is optimal to use only interface events as precursors. In forecasting major crustal events, it is optimal to use only crustal events as precursors. For the smoothed-seismicity component of the EEPAS model, it is optimal to use slab and interface events for earthquakes in the slab, interface events only for earthquakes on the interface, and crustal and interface events for crustal earthquakes. The optimal model parameters indicate that the precursor areas for slab earthquakes are relatively small compared to those for earthquakes in other tectonic categories, and that the precursor times and precursory earthquake magnitudes for crustal earthquakes are relatively large. The optimal models fit the learning data sets better than the raw EEPAS model, with an average information gain per earthquake of about 0.4. The average information gain is similar in the testing period, although it is higher for crustal earthquakes and lower for slab and interface earthquakes than in the learning period. These results show that earthquake interactions are stronger between earthquakes of similar tectonic types and that distinguishing tectonic types improves forecasts by enhancing the depth resolution where tectonic categories of earthquakes are vertically separated. However, when depth resolution is ignored, the model formed by aggregating the optimal forecasts for each tectonic category performs no better than the raw EEPAS model.
