Sizeable Earthquakes Research Articles

Implications for fault locking south of Jakarta from an investigation of seismic activity along the Baribis fault, northwestern Java, Indonesia

Recent borehole seismic deployments conducted along the Baribis Fault in northwestern Java reveal that it may be active. In this study, we exploit these data to locate proximal earthquakes using a relative relocation technique, estimate their moment magnitudes using a spectral fitting method and compute their focal mechanisms via waveform inversion. We observe that seismicity in the eastern part of the fault is significantly higher than in the west, where a previous GPS study of the region south of Jakarta demonstrated the existence of high compression rates. These observations imply that the western Baribis Fault is locked, and that neighbouring areas, including southern Jakarta and its surroundings, may be highly vulnerable to future sizeable earthquakes when accumulated elastic strain energy is eventually released during fault rupture. Significantly, the current generation of Indonesia’s national hazard maps have not considered seismicity along the Baribis Fault. Our new results therefore call for an urgent reappraisal of the seismic hazard in northwestern Java that carefully takes into account the Baribis Fault and its earthquake potential, particularly in light of its proximity to Jakarta, a megacity that lies at the heart of one of the most densely populated islands in the world.

Detailed 3D Seismic Velocity Structure of the Prague, Oklahoma Fault Zone and the Implications for Induced Seismicity

AbstractThe 2011 Mw 5.7 Prague earthquake is the second largest induced earthquake in Oklahoma, and occurred after decades of wastewater disposal. The local geological structure that led to the triggering of this large earthquake is not well understood. In this study, tomographic inversion of seismic data recorded by a dense local seismic network resulted in a high‐resolution 3D velocity model with three major layers. The model clearly illuminates the geometry and characteristics of the Meeker‐Prague Fault that hosted the 2011 Prague sequence. A conceptual model is proposed to link the tomographic structure to the triggering process of the sequence. The low‐permeability second layer at ∼1.5–3.5 km may be the key that delays the occurrence of the first sizeable earthquake after decades of wastewater injection. However, a low‐shear‐velocity zone within this layer at the intersection of two major faults could have provided a fluid pathway to facilitate downward fluid propagation.

An Overview of Earthquake Science in Malaysia

This paper highlights the level of earthquake hazard in Malaysia, the challenges in mitigating earthquake hazard and the way forward on how to strengthen earthquake science in Malaysia. Earthquake hazard is regarded as low throughout Malaysia, with the exception of Sabah where it is considered moderate. This elevated level of a hazard was reinforced during the 2015 Ranau Earthquake, which killed 18 people. Despite this and other recent sizeable earthquakes, the earthquake hazard in Malaysia is poorly understood, yet the population has increased, and growth in buildings and infrastructure has risen. While much progress has been made since the 2015 Ranau earthquake in terms of the development of (i) national seismic hazard map; (ii) national seismic building code; and (iii) planning guideline in a high-risk earthquake area, there are still many challenges faced in mitigating earthquake hazard in Malaysia. There is still a lack of seismic, geological, geodetic and engineering data; insufficient seismic and geodetic monitoring network system; lack of trained human resources; and lack of public awareness. To ensure that earthquake hazard is properly quantified and mitigated some steps have to be taken, which includes (i) comprehensive geological, geotechnical and engineering studies; (ii) coordinated seismic and geodetic monitoring; (iii) human resource capacity building; (iv) coordinated public education; (v) allocation of special research and development grant; and (vi) setting up of a National Earthquake Research Centre.

Correlation between the water temperature and water level data at the Lijiang well in Yunnan, China, and its implication for local earthquake prediction

Anomalous changes in groundwater have been long reported prior to some sizable earthquakes. Here we examined the water temperature and water level data at the Lijiang well in Yunnan, China from November 1, 2007 to September 30, 2017, and obtained the correlation coefficients between them varying with time by using different time windows. We then use Molchan’s error diagram to obtain the area skill scores for different alarm sizes and distances, which are used for evaluating the prediction efficiency of local sizable earthquakes. We found that (i) when the time window is 90 days and the correlation coefficient is greater than 0.10, a sizable earthquake (M ≥ 5.0) is more likely to happen within 200 km during the following 45 days; (ii) when the time window is 90 days and the correlation coefficient is greater than 0.65, a sizable earthquake (M ≥ 5.0) is more likely to happen within 150 km during the following 45 days. Because there are two separate aquifers and the water temperatures become warmer with depths larger than 200 m, we speculate that normally the well water is recharged mainly by colder rainfall through the shallow aquifer, and increasing water level causes decreasing water temperature and vice versa. However, before a local sizeable earthquake (M ≥ 5.0) within 200 km, there may be deep hotter water flowing into and out of the well through the deep aquifer and breaking the negative correlation between them, and positive correlation coefficients are even observed. This study may provide some useful clues for short to medium-term forecast of sizable earthquakes in the Lijiang region and can provide methodological reference for similar studies in other regions.

Assessing the Potential Earthquake Precursory Information in ULF Magnetic Data Recorded in Kanto, Japan during 2000-2010: Distance and Magnitude Dependences.

In order to clarify ultra-low-frequency (ULF) seismomagnetic phenomena, a sensitive geomagnetic network was installed in Kanto, Japan since 2000. In previous studies, we have verified the correlation between ULF magnetic anomalies and local sizeable earthquakes. In this study, we use Molchan’s error diagram to evaluate the potential earthquake precursory information in the magnetic data recorded in Kanto, Japan during 2000–2010. We introduce the probability gain (PG′) and the probability difference (D′) to quantify the forecasting performance and to explore the optimal prediction parameters for a given ULF magnetic station. The results show that the earthquake predictions based on magnetic anomalies are significantly better than random guesses, indicating the magnetic data contain potential useful precursory information. Further investigations suggest that the prediction performance depends on the choices of the distance (R) and size of the target earthquake events (Es). Optimal R and Es are about (100 km, 108.75) and (180 km, 108.75) for Seikoshi (SKS) station in Izu and Kiyosumi (KYS) station in Boso, respectively.

The Last and Most Developed Naṣrid Palace in the Alhambra: The Alijares and Its Country Estate (Fourteenth Century)

ABSTRACTThe country estate (al-munya, almunia in Spanish) of the Alijares occupied grounds near the Alhambra and the Generalife, although it was higher up. It was constructed at the peak of the Naṣrid dynasty's splendour, during the last stage of the reign of Muḥammad V (r.1354–1359 / 1362–1391), after he had finished the Palace of the Lions.The Alijares formed the last link in the chain in the stylistic development of the palaces of al-Andalus. When its founder decided on the features of the Alijares, he was in search of something that was completely innovative, as he had already undertaken work in the medinas of Granada and in the Alhambra that turned out to be a transformation of the architectural forms so far developed.Life in the palace and the al-munya was cut short by sizeable earthquake in 1431, which coincided with a hard Castilian military campaign against the Kingdom of Granada. The consequences of the allegiance formed after the Naṣrid defeat hindered the reconstruction of the Alijares, and so the royal buildings above the Royal Water Channel (Acequia Real) of the Alhambra were abandoned. Although time has erased many of the traces of the palace and its al-munya, we have extensive knowledge of its main architectural features, thanks to an analysis of all the available sources.

Investigation of ULF Seismo-Magnetic Phenomena in Kanto, Japan During 2000–2010: Case Studies and Statistical Studies

In order to clarify the ultra low frequency (ULF) seismo-magnetic phenomena, a sensitive geomagnetic network has been installed in Kanto, Japan. In this study, we have analyzed geomagnetic data observed during the past decade in Izu and Boso Peninsulas. Energy of ULF geomagnetic signals at the frequency around 0.01 Hz has been investigated by wavelet transform analysis. To identify anomalous changes in ionospheric disturbances, the station Memabutsu has been chosen as a reference station. Case studies of magnitude 6 class earthquakes have demonstrated that there are unusual geomagnetic energy enhancements in the vertical component before the main shocks. Statistical studies by superposed epoch analysis have indicated that, before a sizeable earthquake, there are clearly higher probabilities of ULF anomalies than after the earthquake: statistical results of daily counts were found significant at about 3–4 weeks before, 1 week before, few days before, and 1 day after the event for Seikoshi station in Izu and around 2 weeks before, few days before, and 1 day after the event for Kiyosumi station in Boso, respectively.

First evidences of fast creeping on a long-lasting quiescent earthquake normal-fault in the Mediterranean

SUMMARY A key issue in our understanding of the earthquake cycle and seismic hazard is the behaviour of an active fault during the interseismic phase. Locked and creeping faults represent two end-members of mechanical behaviours that are given two extreme rupturing hazard levels, that is, high and low, respectively. Geophysical and space geodetic analyses are carried out over the Pollino Range, an extensional environment within the Africa–Eurasia plate boundary, to disclose the behaviour of the long-lasting quiescent Castrovillari normal fault. Fault trenching evidenced at least four large earthquakes (6.5–7.0 Mw) in the past and an elapsed time of 1200 yr since the last event. Inversion of Differential Interferometric Synthetic Aperture Radar and Global Positioning System over a decade shows fast creeping at all depths of the fault plane. The velocity-strengthening creeping zone reaches maximum rates 20 mm yr −1 against an average rate of about 3–9 mm yr −1 . It limits the southern-weakening locked part of the fault. An essential condition for the generation of a large earthquake on the Castrovillari fault, as has occurred in the past, is a rupture through the velocity-strengthening zone. The Castrovillari fault yields the best evidence for being both a strong and weak fault during its earthquake cycle. Creeping at rates faster than its tectonically driven ones, it must thus consist of a mix of unstable and conditionally stable patches ready to sustain a sizeable earthquake. Quantifying and mapping the slip rate over the fault plane is important because they influence fault moment budget estimate and helps to constrain constitutive laws of fault zones. Aseismic slip also redistributes stress in the crust, thereby affecting the locations of future earthquakes.

Soft-Computing Modelling of Seismicity in the Southern Hellenic Arc

This letter investigates the possible coalition of time intervals and patterns in seismic activity during the preparation process of consecutive sizeable seismic events (i.e., M S ges 5.9). During periods of low-level seismic activity, stress processes in the crust accumulate energy at the seismogenic area, while larger seismic events act as a decongesting mechanism that releases considerable amounts of that energy. Monthly mean seismicity rates have been introduced as a tool to monitor this energy management system and to divert this information into an adaptive neuro-fuzzy inference system. The purpose of the neuro-fuzzy model is to identify and to simulate the possible relationship between mean seismicity rates and time intervals among consecutive sizeable earthquakes. Successful training of the neuro-fuzzy model results in a real-time online processing mechanism that is capable of estimating the time interval between the latest and the next forthcoming sizeable seismic event.

Costs and benefits of earthquake prediction studies in Greece

For the following reasons, a (hypothetical) successful earthquake prediction in Greece would be of, at best, limited benefit to society. (1) On average, less than 5 per cent of sizeable earthquakes (that is magnitude greater than 4.5) cause significant damage or loss of life. (2) Organized evacuation of urban centres is unlikely to be successfully accomplished, because the public lacks confidence in the authorities and cannot be expected to respond promptly; panic and other undesirable side-effects can also be anticipated. (3) The lead time between a short-term prediction and earthquake occurrence is too short for most actions aimed at reducing or eliminating primary or secondary earthquake effects; in any case, most such actions would be superfluous if appropriate longer-term preparedness plans were implemented. (4) Prediction of ‘an earthquake’ is not an appropriate objective in an area such as Greece, which experiences complicated and long seismic sequences consisting of several destructive events, and large earthquakes with anomalous meizoseismal areas. (5) The seismic death toll in Greece is relatively small (less than 10 people per year over the last 40 years), and due to recent changes in building styles and construction practices, current morbidity is mainly associated with the failure of multistorey buildings. This death toll could be more effectively eliminated by identifying weaknesses and structural intervention than by earthquake prediction. Hence, earthquake prediction in Greece, even if it were scientifically feasible, would not be cost-effective; alternative use of funding could be expected to save more lives with much greater certainty. Over the past 15 years, the VAN group's research on earthquake prediction has absorbed a substantial fraction of the resources devoted to earthquake research and protection in Greece. However, the VAN method has not advanced the nation's policy on earthquake protection planning, its results continue to be widely questioned by both the Greek and international scientific communities, and the underlying model is not commensurate with currently accepted thinking on earthquake generation and tectonophysics. Thus, VAN's methods can be regarded as basic research rather than as an operational method for the reduction of seismic risk.

Tsunami recorded on the open ocean floor

On March 14, 1979 a sizeable earthquake (Ms = 7.6, Richter scale) occurred on the continental shelf adjacent to S.W. Mexico, near Petatlan in the state of Guerrero. This earthquake generated a small tsunami that was recorded in deep water, 1000 km away, thus providing for the first time a glance at a tsunami traveling in the open ocean. The same sea floor pressure record displays conspicuous signals associated with vertical sea floor motions generated at the passage of the first Rayleigh seismic wave, R1. Seismic and tsunami travel velocities are in agreement with our present understanding of the phenomena, and tsunami detectability in deep water is demonstrated to be well within present day state of the art in the design of sea floor pressure transducers. As calculations anticipate, the E.M. signals associated with the passage of the tsunami were too faint to be detected.

Seismicity and lithospheric stress in New York and adjacent areas

The earthquake distribution obtained by a relatively dense network of short-period high-gain stations in New York and adjacent areas from 1971 to mid-1976 shows nearly all of the features of seismicity maps from standard listings from 1928 to 1975. In addition, the network data show a region of significant activity in the Adirondack Mountains of northern New York and several sizeable earthquakes in western Lake Ontario. In both areas, few or no earthquakes were previously reported. Both epicentral maps show a region of low seismicity in the Vermont section of the control-versial Boston-Ottawa seismic zone. Well-located earthquakes in the northeastern United States and southeastern Canada range in depth from near surface to about 25 km. Deeper earthquakes (>10 km) have not been found throughout the region, but may be localized in those areas where large earthquakes have occurred. They may also be indicative of deep fault zones which have a greater potential for the occurrence of future large earthquakes. Single events, main shock-aftershock sequences, and swarms are found in this region. We do not yet understand why particular types of earthquake sequences occur in specific areas. In many cases, aftershock sequences or earthquake swarms can be related to mapped faults or inferred extensions of faults. Recent stress indicators in New York and adjacent areas support the presence of an ENE-trending maximum compressive stress in the lithosphere west of the Appalachian Mountains in New York, Ohio, and southern Ontario. The eastern boundary of this stress domain is suggested by limited data in northern New England, southeastern New York, and New Jersey. We postulate that variations in the stress field, which may exist near the eastern boundary of this stress domain, and the general lack of suitably oriented faults in Vermont may explain the region of low seismicity in Vermont along the proposed Boston-Ottawa seismic zone.