Impending Earthquake Research Articles

Different Fault Response to Stress during the Seismic Cycle

Seismic prediction was considered impossible, however, there are no reasons in theoretical physics that explicitly prevent this possibility. Therefore, it is quite likely that prediction is made stubbornly complicated by practical difficulties such as the quality of catalogs and data analysis. Earthquakes are sometimes forewarned by precursors, and other times they come unexpectedly; moreover, since no unique mechanism for nucleation was proven to exist, it is unlikely that single classical precursors (e.g., increasing seismicity, geochemical anomalies, geoelectric potentials) may ever be effective in predicting impending earthquakes. For this reason, understanding the physics driving the evolution of fault systems is a crucial task to fine-tune seismic prediction methods and for the mitigation of seismic risk. In this work, an innovative idea is inspected to establish the proximity to the critical breaking point. It is based on the mechanical response of faults to tidal perturbations, which is observed to change during the “seismic cycle”. This technique allows to identify different seismic patterns marking the fingerprints of progressive crustal weakening. Destabilization seems to arise from two different possible mechanisms compatible with the so called preslip patch, cascade models and with seismic quiescence. The first is featured by a decreasing susceptibility to stress perturbation, anomalous geodetic deformation, and seismic activity, while on the other hand, the second shows seismic quiescence and increasing responsiveness. The novelty of this article consists in highlighting not only the variations in responsiveness of faults to stress while reaching the critical point, but also how seismic occurrence changes over time as a function of instability. Temporal swings of correlation between tides and nucleated seismic energy reveal a complex mechanism for modulation of energy dissipation driven by stress variations, above all in the upper brittle crust. Some case studies taken from recent Greek seismicity are investigated.

Atmospheric and ionospheric disturbances associated with the M > 6 earthquakes in the East Asian sector: A case study of two consecutive earthquakes in Taiwan

The phenomenon of Lithosphere-Ionosphere coupling is a popular topic for researchers for the last two decades. This study aims to analyze the seismo-ionospheric anomalies (SIAs) in East Asia induced by the M > 6 earthquakes (EQs) from Total Electron Content (TEC) of permanent IGS stations operating around the vicinity of the corresponding epicenters by considering a case study of two successive EQs from Taiwan. Our results showed remarkable TEC enhancements one day before both impending EQs during quiet geomagnetic activity (Kp less than 3, Dst ≥ −20), where the variations were found one day before each EQ during UT = 02–08 (LT = 10–16) hours in the form of differential TEC (dTEC). On the other hand, V-shaped gradual decreases in temporal atmospheric parameters took place one day before the M 6.1 EQ that gradually decreased till the M 6.4 EQ day before turning back to normal. The anomaly maps of geopotential height and surface air temperature showed intense decreases and the consequent OLR enhancements right along the edge of the Philippine Sea plate in the northwest direction. Furthermore, we observed a distinctive phenomenon of equatorial ionization anomaly (EIA) enhancement in the latitudinal GIM-TEC profiles near the epicentral longitude, where the EIA structure modified the shape as a double crust structure with a trough near to the equator that testifies the generation of the seismogenic electric field. Our multi-precursory study is another contribution in the acknowledgment of LAI coupling (Lithosphere, Atmosphere, Ionosphere) hypothesis in the prediction of the future EQs.

Artificial Neural Network based thermal anomalies associated with earthquakes in Pakistan from MODIS LST

There are several reports about thermal anomalies associated with the impending earthquakes (EQs); among which the underlying mechanism is linked with the main shock with long, intermediate and short-term precursors. In this paper, we analyzed thermal anomalies from Moderate Resolution Imaging Spectroradiometer (MODIS) based Land Surface Temperature (LST) of three different magnitudes and shallow depth EQs in Pakistan. Our focus is to investigate the thermal anomalies by the statistical approach and Artificial Neural Network (ANN) in spatial and temporal LST values within 10 days before and after the main shock as short-term precursors. After implementing statistical and the ANN approach, LST revealed that thermal anomalies occurred within 1–10 days before the main shock of Mw > 6.0 EQs. However, a low intensity LST anomaly is also recorded within 20–25 days before the main shock of Mw 5.2 EQ. We study that LST anomalies are magnitude and depth dependent and it is more likely to occur before EQ of Mw > 6.0 and shallow depth within 10 days before/after the main shock day. The results depict that Mw 5.2 EQ anomaly is not clearly associated to the main shock, as it locates outside the window of 1–10 days before/after the main shock. Similarly, two out of three events caused post-seismic thermal anomalies of less magnitude as compared to the pre-seismic thermal anomalies. The pre-seismic LST anomalies occur with high intensity before shallow depth and large magnitude EQs than post seismic LST anomalies. The LST anomalies occurred before all the EQs suggesting it to be a reliable precursor of short to intermediate interval associated with an impending EQ.

Man-made earthquakes prevention through monitoring and discharging of their causative stress-deformed states

Despite our understanding of the different mechanisms of man-made earthquakes, their short-term prediction and prevention is yet to be attained. In the present study, we propose an integrated four-step approach to predict and prevent man-made earthquakes or reduce their chance of occurrence. Our four-step approach includes locating the highly anomalous zones of microseismic emission (MSE) that result from the stress-deformed state inside a geological formation and often represents the “seismic nuclei” for impending earthquakes, monitoring the variations and dynamics of the anomalous MSE zones over a period of one lunar month, inducing a creep-discharging of the MSE zones using a vibroseis seismic source at the ground surface, and monitoring the same MSE zones following the creep-discharge to determine whether the stress-deformed state was released and the chance of potential earthquake occurrence has been eliminated or reduced. The proposed full four-step approach has never implemented at one single location. Nevertheless, these steps have been tested separately at different sites and have proven successful. We propose conducting the full four-step approach at various locations of potential man-made earthquake activities around the world including the state of Oklahoma in the USA.

Evaluation of Pre-Earthquake Anomalies of Borehole Strain Network by Using Receiver Operating Characteristic Curve

In order to monitor temporal and spatial crustal activities associated with earthquakes, ground- and satellite-based monitoring systems have been installed in China since the 1990s. In recent years, the correlation between monitoring strain anomalies and local major earthquakes has been verified. In this study, we further evaluate the possibility of strain anomalies containing earthquake precursors by using Receiver Operating Characteristic (ROC) prediction. First, strain network anomalies were extracted in the borehole strain data recorded in Western China during 2010–2017. Then, we proposed a new prediction strategy characterized by the number of network anomalies in an anomaly window, Nano, and the length of alarm window, Talm. We assumed that clusters of network anomalies indicate a probability increase of an impending earthquake, and consequently, the alarm window would be the duration during which a possible earthquake would occur. The Area Under the ROC Curve (AUC) between true predicted rate, tpr, and false alarm rate, fpr, is measured to evaluate the efficiency of the prediction strategies. We found that the optimal strategy of short-term forecasts was established by setting the number of anomalies greater than 7 within 14 days and the alarm window at one day. The results further show the prediction strategy performs significantly better when there are frequent enhanced network anomalies prior to the larger earthquakes surrounding the strain network region. The ROC detection indicates that strain data possibly contain the precursory information associated with major earthquakes and highlights the potential for short-term earthquake forecasting.

Seismotectonic Snapshots: The 18 March 2020 Mw 5.7 Magna, 31 March 2020 Mw 6.5 Stanley, and 15 May 2020 Mw 6.5 Monte Cristo Intermountain West Earthquakes

AbstractSeismological characteristics of the 18 March 2020 Mw 5.7 Magna, 31 March 2020 Mw 6.5 Stanley, and 15 May 2020 Mw 6.5 Monte Cristo Intermountain West earthquakes are largely consistent with expectations arising from observations accumulated over the ∼40 yr since implementation and subsequent growth of seismic networks in the broad region. Each occurred within a zone of relatively elevated seismicity, active faults, and geodetically observed strain accumulation. Aftershock distributions in each are confined primarily to depths of <15 km, and the total number of aftershocks correlates with the relative size of the events. In each case, the number per day decays exponentially in the days following the mainshock. None of the mainshocks was preceded by a foreshock sequence that delivered a plausible warning of the impending earthquakes. With respect to tectonics, each earthquake brings new insights. The Stanley and Monte Cristo earthquakes are at the margins of geodetically defined regions of right-lateral transtension, though the pattern of faulting in each region is markedly different. The strike-slip mechanism of the Stanley earthquake stands in contrast to the zone of normal major range bounding faults and historical earthquake ruptures that characterize the region in which it occurred and is the first relatively well instrumented event to show a rupture extending northward through the Trans-Challis fault system. The Magna event has been interpreted to represent low-angle normal slip near the base of a listric Wasatch range bounding fault (Pang et al., 2020). The east-striking left-lateral Monte Cristo earthquake within the Walker Lane is in contrast to the major northwest-striking right-lateral faults that dominate the area, though predictable from prior regional mapping. Surface rupture reportedly accompanied only the Monte Cristo earthquake, though its trace does not clearly follow the zone of aftershocks.

A paradigm for developing earthquake probability forecasts based on geoelectric data

We examine the precursory behavior of geoelectric signals before large earthquakes by means of a previously published algorithm including an alarm-based model and binary classification [H.-J. Chen, C.-C. Chen, Nat. Hazards 84, 877 (2016)]. The original method has been improved by removing a time parameter used for coarse-graining of earthquake occurrences, as well as by extending the single-station method into a joint-stations method. Analyzing the filtered geoelectric data with different frequency bands, we determine the optimal frequency bands of earthquake-related geoelectric signals featuring the highest signal-to-noise ratio. Based on significance tests, we also provide evidence of a relationship between geoelectric signals and seismicity. We suggest using machine learning to extract this underlying relationship, which could be used to quantify probabilistic forecasts of impending earthquakes and to get closer to operational earthquake prediction.

Infrared Emission from rocks in the Thermal Infrared (TIR) window

Satellite data provide ground surface temperatures based on the intensity of the thermal infrared (TIR) emission. TIR anomalies that appear to be related to impending earthquake activity were first reported more than 25 years ago. They can reach 10–15 K. To account for such temperature anomalies, it has been widely assumed that, prior to major earthquakes, warm gases or radon are emanating from the ground around the future epicenter. Here a radically different explanation is presented based on the growing evidence that rocks in the Earth's crust contain peroxy defects in their constituent mineral grains. Peroxy defects consist of pairs of tightly coupled O− such as in O3Si-OO-SiO3. Upon application of stress the electrically inactive peroxy defects can break up, releasing highly mobile electronic charge carriers: defect electrons in the O2-sublattice, called positive holes, symbolized by h•. The h• are the electronic wave function associated with O− in a matrix of O2−. They have the remarkable ability to flow out of the stressed rock volume, spreading fast and far. At the Earth's surface the h• become trapped, preferentially at topographic highs. As they recombine, returning to the peroxy state, IR photons of specific energies are emitted in the Thermal Infrared (TIR) window. In laboratory and field experiments rocks were subjected to stress either by loading one end of a rectangular chunk of a black quartz-bearing diorite via a hydraulic press or by stressing granite boulders from the inside out via expanding BUSTAR cement in boreholes. The TIR emission was recording during the build-up of stress up to failure of the rocks. Principal components analysis and a novel application of fluctuation spectroscopy identified several previously unknown phenomena, in particular a series of TIR emission bands that are consistent with the radiative de-excitation of vibrationally “hot” states of peroxy bonds forming at the rock surface and to pink noise suggestive of electron/hole trapping like in semiconductors.

Mechanism of unipolar electromagnetic pulses emitted from the hypocenters of impending earthquakes

Unipolar pulses (UPs) are short events characterized by outbursts of electromagnetic (EM) energy from deep within the Earth's crust. First recognized prior to the 2007 M = 5.4 Alum Rock earthquake in northern California, UPs can be as short as 150ms, followed by an overshoot in the opposite polarity direction or by undulations of the EM field lasting from to 2−20 sec. Near Lima, Peru, and Tacna, Peru, thousands of UPs in the 1−3 nT intensity range have been recorded, emitted from the 25−65km depth range, thought to arise in patches at the top of the Benioff Zone of the subducting Nazca Plate. To understand how these EM pulses can be generated deep in the rock column, we consider that rocks contain peroxy defects, typically O3Si−OO−SiO3, which, when subjected to increasing deviatoric stresses, break up in two steps. Step I: electrons in the tight non-bonding πnb molecular orbital decouple by transitioning into the antibonding σ*-level, where they occupy a significantly larger volume. This volume expansion is possible only, when the internal pressure in the stressed subvolume overcomes its confining pressure. This in turn requires that the number density of peroxy defects in the rock is high enough so that, during the πnb → σ* transition of the O−−O− bonds, the wave function of their decoupled O− states overlap, causing a solid plasma state with an internal electron degeneration pressure that can force the volume expansion against the load of the overlying rock column. Step II: once the σ*-level is reached, the decoupled O−−O− bonds can dissociate, generating highly mobile charge carriers, electrons e' and holes h•, which can burst out the stressed subvolume causing it to instantly contract again. Thus, UPs appear to be linked to an explosive expansion of stressed subvolumes of rocks against their lithostatic overload, followed by an outburst of electronic charge carriers and concomitant volume contraction.

Stress level monitoring using SWS measurements of local earthquakes of Garhwal Himalaya

Chamoli district of Garhwal Himalaya is one of the highly seismically active region and probable zone for impending great earthquake in the CSG. In the present study, to understand the upper crustal anisotropy of Chamoli region, shear wave splitting (SWS) analysis is performed for local seismic events. Forevents > 2 MreportedatGhuttu station during the period Nov 2014 to JULY 2015, SWSparameters aremeasured. A considerable temporal difference in delay time was observed during the SWS study with respect to the 4.9Mw magnitude earthquake that occurred in the Chamoli region on 1st April 2015 at 21:23 hrs (UTC). A rise in delay time prior to the earthquake which decreases steadily over time is observed at GTU station. This decrease in delay time can be related to the region’s stress relief. The calculated average delay time (δt) is 3.83 ms/km and a maximum value of 5.37 ms/km for the earthquake of magnitude 4.9Mw. Sfast polarization direction range from N120° to N170° has been observed for the majority of the earthquakes. An average NW-SE orientation of the shallow subsurface micro-cracks along the ray path beneath the Chamoli region has also observed. Present study is a step towards earthquake precursory research in Garhwal-Kumaun region for monitoring of the state of accumulated stress. This study clearly demonstrate that SWS measurements for local earthquakes can be utilized for continuous monitoring of temporal variation in time delay (δt) and probably used for stress forecast for an impending earthquake.

Geometrically controlled slow slip enhanced by seismic waves: A mechanism for delayed triggering

Seismic waves generated during earthquakes induce transient stress changes in the crust. These ephemeral perturbations can trigger critically stressed asperities at remote distances, often with significant time delays. The physical mechanism that governs this phenomenon is not completely resolved. Numerical simulations of dynamic perturbations passing along a heterogeneous pre-stressed fault, demonstrate that weak portions of the fault that host ongoing slow slip can transfer stress in response to the perturbations, loading asperities poised for failure. We find that the magnitude of perturbation, the state of the asperity, as well as deformation of the surrounding material, jointly control the delay time between perturbation and triggered event. The slow-slip modulated delayed triggering model that we propose can account for the wide range of observed delay times in nature, including the two end-member cases of no delay and no triggering. Triggered slow slip events in nature might provide warning signs of impending earthquakes, underscoring the importance of high-resolution monitoring of active fault zones.

A possible precursor prior to the Lushan earthquake from GPS observations in the southern Longmenshan

Global Positioning System (GPS) stations installed in and around the epicenter of the Lushan earthquake (Mw 6.7), which occurred almost 5 years after the 2008 Wenchuan earthquake, recorded preseismic deformation corresponding to the Lushan earthquake within the southern Longmenshan thrust belt. A half-space dislocation model is used to simulate the theoretical values of the postseismic displacements caused by the 2008 Wenchuan earthquake, and after transforming the reference frame and filtering the GPS displacement time series, the theoretical and observed GPS values are compared to identify the geodetic anomaly preceding the Lushan earthquake. The abnormal extent of this geodetic anomaly decreases with increasing epicentral distance for each GPS site. This geodetic signal reflects preslip along a locked section of the 2013 seismogenic fault, which caused the accumulation of elastic strain energy until the faulting strength was overcome, thereby generating the Lushan earthquake. Hence, this anomaly might be used as an observable and identifiable precursor to forecast an impending earthquake within a period of less than two and half years before its occurrence.

Determination of Epicenters before Earthquakes Utilizing Far Seismic and GNSS Data: Insights from Ground Vibrations

Broadband seismometers, ground-based Global Navigation Satellite Systems (GNSS), and magnetometers that were located within an epicentral distance of approximately 150 km consistently observed the novel anomalous behaviors of the common-mode ground vibrations approximately 5–10 days before the M6.6 Meinong earthquake in Taiwan. The common-mode ground vibrations with amplitudes near 0.1 m at frequencies ranging from 8 × 10−5 to 2 × 10−4 Hz were generated near the region close to the epicenter of the impending earthquake. The common-mode vibrations were consistently observed in seismic and GNSS data associated with five other earthquakes in four distinct areas. The results reveal that the common-mode vibrations could be a typical behavior before earthquakes. The causal mechanism of common-mode vibrations can be attributed to crustal resonance excitations before fault dislocations occur. Potential relationships with other pre-earthquake anomalies suggest that the common-mode vibrations could be ground motion before earthquakes, which was investigated for a significant length of time.

A case study: the relationship between 222Rn in rainwater and earthquakes according to air masses

The relationship between radon gas and earthquake behavior is widely researched by investigating 222Rn (Radon-222) in air, soil, and water. This study is aimed at proving that 222Rn concentration in rain water and in the movement of rain systems will give an indication of impending earthquakes. The study was conducted in predetermined areas in the west of Anatolia. It is found that 222Rn in rain water was between 0.021 and 0.647 Bq/l for a year in Bornova. Besides, it is shown that the origin of air masses that affect the area are covered in this study and synoptic and climatologic analysis of these air masses as well as thunderstorms and strokes are presented in this study. It is found from the analysis that the information of earthquake is transported by the presence of radon gas with rain water in the predetermined area, approximately a radius of 97 km area.

Piezoelectricity as a mechanism on generation of electromagnetic precursors before earthquakes

SUMMARYTo produce the electromagnetic (E&M) precursors of an earthquake, the existence of electric field due to stress-induced charges on the ground surface or in shallow depths of upper crust inside the fault zone is a basic condition. Here, we consider the piezoelectric effect or the elastic–electric coupling as a major mechanism on generating such an electric field. A 1-D model based on the elastic mechanics and electromagnetic Maxwell equations is built up to formulate the relationship between electric field and slip as well as stress on a fault before an earthquake. From the model, we may estimate the low-bound values of stress and slip to yield the critical electric field, Ec, for generation of electromagnetic signals. The normal and shear stresses on the fault planes for three faulting types are constructed. The normal stress is stronger than the shear stress to result in piezoelectricity. The depth ranges for yielding an average normal stress being able to generate Ec are similar for thrust and strike-slip faults and deep for normal faults. The possibility of generating Ec is almost the same for thrust and strike-slip faults and low for normal faults. The pre-earthquake slip could be related to nucleation phases or microfractures. The possible occurrence time of E&M signals may be several 10 min to few hours before impending earthquakes. The major factor in yielding a piezoelectric field to generate the TEC anomalies before an earthquake is the existence of fault gouges composed mainly of clays. A thick gouge layer with low electric resistivity and a piezoelectric coupling coefficient ≥0.67 × 10−12 coul nt–1 is an important condition for yielding piezoelectricity.

Ionosonde Data Analysis in Relation to the 2016 Central Italian Earthquakes

Ionospheric characteristics and crustal earthquakes that occurred in 2016 next to the town of Amatrice, Italy are studied together with the previous events that took place from 1984 to 2009 in Central Italy. The earthquakes with M larger than 5.5 and epicentral distances from the ionosonde less than 150 km were selected for the analysis. A multiparametric approach was applied using variations of sporadic E-layer parameters (the height and the transparency frequency) together with variations of the F2 layer critical frequency foF2 at the Rome ionospheric observatory. Only ionospheric data under quiet geomagnetic conditions were considered. The inclusion of new 2016 events has allowed us to clarify the earlier-obtained seismo-ionospheric empirical relationships linking the distance in space (km) and time (days) between the ionospheric anomaly and the impending earthquake, with its magnitude. The improved dependencies were shown to be similar to those obtained in previous studies in different parts of the world. The possibility of using the obtained relationships for earthquake predictions is discussed.

Simulation of strong ground motion due to active Sohna fault in Delhi, National Capital Region (NCR) of India: an implication for imminent plausible seismic hazard

Delhi, National Capital Region (NCR) of India, falls in the seismic Zone IV (Zone factor 0.24) on the seismic zoning map prepared by the Bureau of Indian Standards (BIS), and this region may experience devastating intensities in case of plausible moderate to the major earthquake in the vicinity. The strategic geological, geomorphological, and geographic characteristics make this seat of administrative power more vulnerable toward the earthquake disaster right from the ancient periods. Therefore, we study the impact of the M 6.0 earthquake sourced at Sohna fault in the neighborhood of the capital region by generating synthetic accelerograms through semiempirical envelop technique. The observed accelerograms of November 25, 2007 ( $$M_{w}$$ 4.7) earthquake have been modeled to utilize the reliability of the semiempirical approach. To analyze the actual scenario, the ground motions at the surface have been generated after the incorporation of the site effects because different soil conditions of NCR fascinate different degrees of damage in case of a destructive earthquake. As a result, the obtained peak ground acceleration (PGA) varies between 100 and 600 cm/s2, and some of the sites exhibit even higher PGA values being situated on the sediments of river-oriented plain areas and proximity of the source. The spatial distribution of estimated values of PGA and spectral accelerations at different periods show that sites in NCR like Delhi (600 cm/s2), Sonipat (633 cm/s2), Gurgaon (461 cm/s2), and Faridabad (300 cm/s2) exhibit high to severe seismic hazard in case of M 6.0 at Sohna fault and it is suggested that a population of about 4.78 million along with the infrastructure of this region is exposed to high risk. The estimated seismic exposure of the population is important to utilize the resources properly before the destructive earthquake incidence. The hazard maps for PGA and different structural periods in the NCR region reveal the level of seismic hazard and risk of the study region. These hazard maps are very helpful for administrators, stakeholders, and civil engineers to construct earthquake-resistant structures to minimize the risk generated by the future impending earthquakes. The exponential growth of the buildings, industries, businesses, etc., attracts the attention of urban area planners because of high seismic risk due to the damaging earthquakes, and its severity must be understood to save the life and property to mitigate the natural disaster like an earthquake by proper disaster mitigation plans, especially in the metropolitan cities like Delhi NCR.

Two Foreshock Sequences Post Gulia and Wiemer (2019)

AbstractRecognizing earthquakes as foreshocks in real time would provide a valuable forecasting capability. In a recent study, Gulia and Wiemer (2019) proposed a traffic-light system that relies on abrupt changes in b-values relative to background values. The approach utilizes high-resolution earthquake catalogs to monitor localized regions around the largest events and distinguish foreshock sequences (reduced b-values) from aftershock sequences (increased b-values). The recent well-recorded earthquake foreshock sequences in Ridgecrest, California, and Maria Antonia, Puerto Rico, provide an opportunity to test the procedure. For Ridgecrest, our b-value time series indicates an elevated risk of a larger impending earthquake during the Mw 6.4 foreshock sequence and provides an ambiguous identification of the onset of the Mw 7.1 aftershock sequence. However, the exact result depends strongly on expert judgment. Monte Carlo sampling across a range of reasonable decisions most often results in ambiguous warning levels. In the case of the Puerto Rico sequence, we record significant drops in b-value prior to and following the largest event (Mw 6.4) in the sequence. The b-value has still not returned to background levels (12 February 2020). The Ridgecrest sequence roughly conforms to expectations; the Puerto Rico sequence will only do so if a larger event occurs in the future with an ensuing b-value increase. Any real-time implementation of this approach will require dense instrumentation, consistent (versioned) low completeness catalogs, well-calibrated maps of regionalized background b-values, systematic real-time catalog production, and robust decision making about the event source volumes to analyze.

Natural Time Analysis of Seismicity within the Mexican Flat Slab before the M7.1 Earthquake on 19 September 2017.

One of the most important subduction zones in the world is located in the Mexican Pacific Coast, where the Cocos plate inserts beneath the North American plate. One part of it is located in the Mexican Pacific Coast, where the Cocos plate inserts beneath the North American plate with different dip angles, showing important seismicity. Under the central Mexican area, such a dip angle becomes practically horizontal and such an area is known as flat slab. An earthquake of magnitude M7.1 occurred on 19 September 2017, the epicenter of which was located in this flat slab. It caused important human and material losses of urban communities including a large area of Mexico City. The seismicity recorded in the flat slab region is analyzed here in natural time from 1995 until the occurrence of this M7.1 earthquake in 2017 by studying the entropy change under time reversal and the variability β of the order parameter of seismicity as well as characterize the risk of an impending earthquake by applying the nowcasting method. The entropy change ΔS under time reversal minimizes on 21 June 2017 that is almost one week after the observation of such a minimum in the Chiapas region where a magnitude M8.2 earthquake took place on 7 September 2017 being Mexico’s largest quake in more than a century. A minimum of β was also observed during the period February–March 2017. Moreover, we show that, after the minimum of ΔS, the order parameter of seismicity starts diminishing, thus approaching gradually the critical value 0.070 around the end of August and the beginning of September 2017, which signals that a strong earthquake is anticipated shortly in the flat slab.

Risk Assessment of Seismic Vulnerability of All Hospitals in Manila Using Rapid Visual Screening (RVS)

Philippine is one of the countries near in the Pacific Ring of Fire. In recent years, several moderate to high seismic activities happened that leads to casualties, deaths and damages in different structures. Manila is the capital of the Philippines with a population of almost 1.8 million. Many structures have been considered as old and unsafe and with an impending earthquake, it is essential to rehabilitate these structures. The imminent danger of the West Valley Fault when it moves is known throughout the metro manila and other neighbouring regions. The damage and casualties that will sustain from the possible 7.2 magnitude earthquake is fatal. Conducting mitigation programs is critical for it will greatly benefit the government and the people. Rapid Visual Screening (RVS) is an effective and efficient way of assessing the building’s structural integrity. This methodology is used to assess the structure’s seismic risk by visual observation of the exterior and interior of the buildings and a data collection form. RVS was applied in 26 hospital building’s located in Manila and the outcome of the assessment has shown that only 6 hospital buildings proved to be seismically adequate when using the level 1 data collection form. RVS is an effective tool in providing initial insight in the building’s vulnerability to seismic event.