No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The earthquake environmental effects (EEEs) of the 6th February 2018, Hualien earthquake (Mw=6.4): A contribution to the seismic hazard estimation in the epicentral area
Abstract
The macroseismic intensity of the February 6, 2018, Mw 6.4, Hualien earthquake, which caused extensive damage around the Hualien area of eastern Taiwan is reassessed using the Environmental Seismic Intensity (ESI-07) scale. We compiled data on earthquake environmental effects (EEEs) caused by the 2018 Hualien earthquake, which includes surface ruptures, ground cracks, liquefaction, and occasional landslides, and estimated the epicentral intensity (I0) as well as site-specific intensities. We found that the ESI-07 epicentral intensity of the Hualien quake in 2018 is IX. We note that the epicentral area of the 2018 Hualien earthquake was the mesoseismal area of the October 22, 1951, (Mw 6.6) Hualien earthquake, as reported in primary contemporary sources and historical earthquake catalogs. The 1951 Hualien earthquakes also caused prominent surface ruptures, liquefaction, and ground cracks. Consequently, we reassess the macroseismic intensities of this historical seismic event and compare it to the Hualien earthquake in 2018. The comparison suggests similar epicentral intensities for the two earthquakes (IX and X ESI-07). Moreover, we conducted a systematic comparison between intensity obtained using different scales which revealed the differences of two to three degrees between the ESI-07 and traditional intensity scales. This result reconfirms the significance of documentation and recording of earthquake environmental effects to make intensity assessments for modern seismic events consistent with the historical earthquake records. Moreover, a re-evaluation of historical earthquake intensity in eastern Taiwan could be performed in order to update the seismic hazard map. Application of the ESI-07 intensity scale of recent and historical earthquakes will be helpful in post-earthquake recovery efforts for a future earthquake. The prepared ShakeMaps from the ESI-07 values suggests completely different shapes to the previously generated ShakeMaps considering the peak ground acceleration or peak ground velocity. It suggests that the ShakeMaps prepared from the earthquake environmental effects can be complemented with the instrumental based intensity map to have a better seismic hazard prediction and future land use planning for the region.
... It is especially beneficial in sparsely populated areas where human and structural impacts may be challenging to document (e.g., Dengler and McPherson, 1993). It allows mapping the distribution of EEEs generated by large seismic events, providing a detailed database suitable for engineering geology applications (Guerrieri et al., 2015;Papathanassiou et al., 2017aPapathanassiou et al., , 2017bKing et al., 2018;Naik et al., 2023aNaik et al., , 2023b. The Mexican subduction zone is an interesting setting to apply the ESI-07 scale, as the population in the coastal areas is regularly affected by extensive primary and secondary effects of major earthquakes (Velázquez-Bucio et al., 2023a;Fig. ...
... As already suggested (Papathanassiou et al., 2017a(Papathanassiou et al., , 2017bMavroulis et al., 2021;Naik et al., 2023aNaik et al., , 2023b, the macroseismic intensity estimation might take advantage of space geodesy technology. In the case of the September 19th, 2022, Michoacan earthquake, we observe that coastal uplift significantly correlates with the region of maximum vertical displacement illustrated by C-band Sentinel-1 satellite synthetic aperture radar (SAR) images (Liu et al., 2023;Fig. ...
... Pantò et al. [11] used a macro-modeling approach to assess masonry arch bridges under earthquake loading. Naik et al. [12] evaluated the environmental effects of the Hualien earthquake. Naik et al. [13] examined the damage in Medieval monuments around New Delhi in detail and proposed a new approach. ...
The Kahramanmaraş (Türkiye) earthquake on 6 February 2023, one of the largest earthquakes of the century, caused the collapse or severe damage of thousands of structures. This catastrophic disaster resulted in over 53,000 fatalities and rendered many structures unusable. This study addresses the observed damage in reinforced concrete (RC) structures, which constituted the majority of the existing urban building stock. In this study, firstly, information about the destructive Kahramanmaraş earthquakes was given. The predicted PGAs in the last two earthquake hazard maps used in Türkiye were compared with the measured PGAs from actual earthquakes to determine whether the earthquake hazard is adequately represented for eleven affected provinces in the earthquake region. The damages in RC structures were evaluated within the scope of civil and earthquake engineering. Structural analyses for the model created to represent mid-rise RC buildings in the region were carried out separately for each province using predicted and measured PGAs. Additionally, target displacements that were used in performance-based earthquake engineering for damage prediction, were examined comparatively for all provinces. While the predicted earthquake hazard and targeted displacements were exceeded in some provinces, there was no exceedance in the other provinces. The realistic representation of earthquake hazards will allow the predicted displacements for various performance levels of structures to be determined in a much more realistic way. Consequently, the performance levels predicted for the structures will be assessed with greater accuracy. The study highlights the importance of accurately presenting earthquake hazards to predict building performance effectively.
... This methodology has been applied in many studies (e.g. Legendre et al. 2017;Mittal et al. 2018;Yang et al. 2018Yang et al. , 2021Naik et al. 2023a;Naik et al. 2024). The Gisenyi earthquake ShakeMap shows a maximum intensity of IX around Rubavu with other affected areas showing an intensity of VIII (Fig. 9). ...
On 26th May 2021, an earthquake with a moment magnitude Mw 5.1 hit the densely populated cities of Gisenyi (Rwanda) and Goma (D.R. Congo) which sit on the active East African Rift System. It was one of the largest earthquakes associated with the 2021 Mount Nyiragongo eruption. Although of moderate magnitude, the earthquake substantially damaged manmade structures. This paper presents field observations on the geotechnical impact, building damage, and factors contributing to the heightened destruction caused by this moderate earthquake. The damage pattern observed in the field indicates that masonry structures with inadequate seismic detailing were the most damaged buildings. In addition, the statistical analysis of the damaged buildings indicates most of the damaged structures were located in plains covered by volcanic soil. The intensity of the waves was estimated using the building damage data based on the European Macroseismic Scale (EMS-98). An intensity distribution map was generated for the surveyed area, suggesting EMS-98 intensity of VIII or IX along the eastern basin boundary fault and VII around the cities of Goma and Gisenyi where the land is composed of black cotton soil of volcanic origin. The higher intensity values along the eastern basin-bounding fault indicate that a reevaluation of the seismic hazard for the region is necessary. Since this is the first-ever such damage survey for the region, the developed intensity map can be used to understand the correlation between the intensity of the ground motion and damage severity which contributed to the seismic hazard assessment of the study area.
The macroseismic intensity of the February 6, 2012, Negros Oriental earthquake (MW 6.7), which affected the islands of Negros and Cebu, central Philippines, has been reassessed in this study using the Environmental Seismic Intensity Scale (ESI-2007). This earthquake caused a ∼75-km-long surface rupture along a previously unmapped fault and resulted in extensive landslides, localized liquefaction, lateral spreading, a tsunami, and widespread damage to infrastructure near the epicentral area. Considering the widespread earthquake environmental effects (EEEs), ESI-2007 intensities were evaluated for 324 locations covering an area of approximately 1000 km² within the Negros and Cebu Islands. A systematic comparison was conducted between the ESI-2007 scale and the traditional intensity scales (PHIVOLCS earthquake intensity scale (PEIS) and Modified Mercalli Intensity scale (MM) along with the generation of an ESI-2007 shake map, which is solely based on site-specific ESI-2007 intensity values. According to the ESI-2007 scale, the epicentral intensity I0=X is assessed. This is two degrees higher than the intensity of the PEIS, and three degrees higher than the modified MM intensity provided by the United States Geological Survey (USGS). The intensity difference may also be due to the lack of suitable observations of building damage data in this sparsely populated region of the Philippines. Comparison of the ShakeMap that was constructed using the ESI-2007 intensities with the PHIVOLCS and USGS ShakeMap suggests that the instrumental or structural damage-based intensity maps underestimate the seismic intensity for the 2012 Negros Oriental earthquake. The ESI-2007 ShakeMap presented in this work is pertinent for the assessment of future seismic risk associated with other earthquake generators in the vicinity of the islands of Negros and Cebu. It can be integrated with the PEIS or MM intensity scale to improve disaster management and planning, post-earthquake recovery efforts, and damage estimation.
A series of earthquakes that struck Taiwan's southern Longitudinal Valley on September 17 and 18, 2022 severely damaged several buildings in Taitung and Hualien. The Chishang earthquake, which had a magnitude of ML 6.8 and a large foreshock with a magnitude of ML 6.6 the day before, was the mainshock in this sequence. The strongest intensity reported in the epicentral region during this earthquake sequence, which was 6+, is the highest ever recorded since the Central Weather Bureau (CWB, renamed as the Central Weather Administration since September 15, 2023) revised its seismic intensity scale. National Taiwan University (NTU) has operated a low-cost earthquake early warning (EEW) system known as the P-Alert for a decade. In this study, we demonstrate the performance of the P-Alert network during the 2022 Chishang earthquake and the largest foreshock. The P-Alert network plotted shake maps during these earthquakes that displayed various values within 5 minutes. The high shaking areas on these maps were in good agreement with observed damages during this earthquake, providing valuable insights into rupture directivity, a crucial component of earthquake engineering. Individual P-Alert stations acted as on-site EEW systems and provided a 3-10 second lead time within the blind zone of CWB. For the ML 6.8 mainshock, there was a lead time of at least 5 s, even up to 10 s, demonstrating their effectiveness in the blind zone. The P-Alert regional EEW system provided the first report about 9 s and 7 s after the mainshock and the largest foreshock occurrence, respectively, with estimated magnitudes of 5.74 and 5.67. The CWB system estimated magnitudes of 6.72 and 6.16 in the first report, respectively, about 7 s and 9 s after the earthquake occurrence. The timeliness of the two systems were not significantly different. Despite the effectiveness of the P-Alert network, data loss due to connection interruptions prompted us to develop a new compact data logger for improved data availability.
Using low-cost sensors to build a seismic network for earthquake early warning (EEW) and to generate shakemaps is a cost-effective way in the field of seismology. National Taiwan University (NTU) network employing 748 P-Alert sensors based on micro-electro-mechanical systems (MEMS) technology is operational for almost the last 10 years. This instrumentation is capable of recording the strong ground motions of up to ± 2g and is dense enough to record the near-field ground motion. It has proven effective in generating EEW warnings and delivering real-time shakemaps to the concerned disaster relief agencies to mitigate the earthquake-affected regions. Before 2020, this instrumentation was used to plot peak ground acceleration (PGA) shakemaps only; however, recently it has been upgraded to generate the peak ground velocity (PGV), Central Weather Bureau (CWB) Intensity scale, and spectral acceleration (Sa) shakemaps at different periods as value-added products. After upgradation, the performance of the network was observed using the latest recorded earthquakes in the country. The experimental results in the present work demonstrate that the new parameters shakemaps added in the current work provide promising outputs, and are comparable with the shakemaps given by the official agency CWB. These shakemaps are helpful to delineate the earthquake-hit regions which in turn is required to assist the needy well in time to mitigate the seismic risk.
The earthquake environmental effects (EEEs) around the epicentral area of the Pohang earthquake (Mw-5.4) that occurred on 15 November 2017 have been collected and classified using the Environmental Seismic Intensity Scale (ESI-07 scale) proposed by the International Union for Quaternary Research (INQUA) focus group. The shallow-focus 15 November Pohang earthquake did not produce any surface rupture, but caused extensive secondary environmental effects and damage to life-line structures. This earthquake was one of the most damaging earthquakes during the instrumental seismic era of the Korean Peninsula. The EEEs included extensive liquefaction, ground cracks, ground settlement, localized rockfall, and variation of the water table. The main objective of this paper was to carry forward a comparative assessment of the Pohang earthquake’s intensity based on traditional macroseismic scales and the ESI-07 scale. With that objective, this study will also make a substantial contribution to any future revision of the ESI-07 scale, which mostly comprises case studies from Europe and South America. The comparison of the ESI-07 scale with traditional intensity scales similar to the intensity scale used by the Korean Meteorological Administration for the epicentral areas showed 1–2-degree differences in intensity. Moreover, the ESI scale provided a clearer picture of the intensity around the epicentral area, which is mostly agricultural land with a lack of urban units or buildings. This study urges the integration of the traditional and ESI-07 scale for such small magnitude earthquakes in the Korean Peninsula as well as around the world in future. This will predict seismic intensity more precisely and hence provide a more-effective seismic hazard estimation, particularly in areas of low seismic activity. The present study will also provide a useful and reliable tool for the seismic hazard assessment of similar earthquakes around the study area and land-use planning at a local scale considering the secondary effects.
An earthquake with an epicenter offshore of Hualien City in eastern Taiwan occurred at midnight on February 6, 2018. The Richter magnitude (ML) of the earthquake was 6.26 and the seismic intensity ranged up to level VII, the strongest seismic intensity level regulated in Taiwan. Almost all the major damage resulting from this seismic event was occurred near both sides of the Milun Fault, where records from nearby strong motion stations displayed the characteristics of near-fault ground motions. The main seismic damage was the collapse of four buildings with soft bottom stories, one of which resulted in fourteen of the seventeen total fatalities. Comparing the acceleration response spectra with the design response spectra sheds light on the effects of near-fault ground motions on the collapsed buildings. Based on the eventual forms of collapsed buildings, building collapses that have generally led to major casualties in past seismic events around the world can be classified into sit-down, knee-down and lie-down types. In addition to the four collapsed buildings, seismic reconnaissance on other buildings, bridges, ports, and non-structural components have also been conducted. This study explores the issues and challenges arising from the reconnaissance results and thereby enhances learning from the seismic event.
The application of the Environmental Seismic Intensity (ESI) scale 2007 to moderate and strong earthquakes, in different geological context all over the word, highlights the importance of Earthquake Environmental Effects (EEEs) for the assessment of seismic hazards. This Special Issue “New Perspectives in the Definition/Evaluation of Seismic Hazard through Analysis of the Environmental Effects Induced by Earthquakes” presents a collection of scientific contributions that provide a sample of the state-of-the-art in this field. Moreover the collected papers also analyze new data produced with multi-disciplinary and innovative methods essential for development of new seismic hazard models.
On 26th January 2001, an earthquake of magnitude Mw 7.7 occurred near Bhuj, in northwestern India, resulting in severe environmental effects. No unequivocal primary surface rupture was observed for the earthquake, but it caused widespread liquefaction and lateral spreading in the Rann of Kachchh and Little Rann. After the earthquake, several researchers collected field evidence of secondary surface rupture, rockfall, dry craters, and surface manifestations of liquefaction, including the formation of mud volcanoes and lateral spreads, in the meizoseismal area. Analysis of pre- and post-earthquake satellite images suggests that several “dry” streams in the Rann of Kachchh began to flow due to extensive liquefaction induced by the earthquake. In this present study, the macroseismic intensity of the Bhuj earthquake is evaluated by considering these environmental effects and applying the ESI-07 intensity scale to the affected area. As an outcome, the epicentral intensity of the 2001 Bhuj earthquake was determined to be XI. According to historical records and seismic catalogs, 16th June 1819 Allah Bund earthquake caused prominent surface rupture which was not so clear in the case of 2001 Bhuj earthquake, but the secondary effects were similar for both earthquakes. Considering the environmental effects caused by the 1819 Allah Bund earthquake, an intensity of XI was estimated for the epicentral area. For both earthquakes, the ESI scale yields a significant difference of one to two degrees with the traditional intensity scales. The 2001 Bhuj earthquake and 1819 Allah Bund earthquake shows similar ESI-07 intensity of XI despite different epicentral locations. This implies the reliability of ESI-07 scale application for different earthquakes of similar dimensions in the same geological setting. This study contributes to the application of ESI-07 scale for Indian earthquakes, especially reverse faulting events, and to the future improvement of the ESI scale with emphasis on its applicability to historical earthquakes on the Indian subcontinent. Also, this study may help in future land use planning in the meizoseismal area of 1919 Allah Bund and 2001 Bhuj earthquakes.
The distributions and characteristics of coseismic surface ruptures are the key to understand fault behaviors. However, traditional field investigations could be time consuming while toppled buildings and infrastructures may be subject to repairs due to rescue missions and transportation recovery within a few days after the earthquake, leading to urgent needs for rapid, extensive surveys before surface breakages are modified. Therefore, we take advantage of UAS photogrammetry to collect aerial images and to map surface fractures for the M w 6.4 Hualien, eastern Taiwan, earthquake on 6 February 2018. The earthquake struck Hualien City and generated dense surface breakages over a distance of ~8 km. Together with control surveys for ground control points by using RTK-GPS, UAS photogrammetry uses the methods of the Structure from Motion and Multi-View Stereo to produce high-resolution orthoimages and digital surface models. Our mapping results show that surface ruptures follow the trace of the Milun fault and northern Linding fault. Mapped surface ruptures are usually in en échelon arrays or distributed fractures rather than a through-going fault. Estimated sinistral offset based on orthoimages is more than 60 cm in Chihsingtan and decreases toward south. The fault behavior of the 2018 Hualien earthquake shows along-strike variations and is somewhat different from the October 1951 earthquake.
A hazard assessment of the 1976 Guatemala earthquake (M = 7.5) was conducted to achieve a better definition of the seismic hazard. The assessment was based on the environmental effects that had effectively contributed to the high destructive impact of that event. An interdisciplinary approach was adopted by integrating: (1) historical data; (2) co-seismic geological effects in terms of Environmental Seismic Intensity (ESI) scale intensity values; and (3) ground shaking data estimated by a probabilistic/deterministic approach. A detailed analysis of primary and secondary effects was conducted for a set of 24 localities, to obtain a better evaluation of seismic intensity. The new intensity values were compared with the Modified Mercalli Intensity (MMI) and Peak Ground Acceleration (PGA) distribution estimated using a probabilistic/deterministic hazard analysis approach for the target area. Our results are evidence that the probabilistic/deterministic hazard analysis procedures may result in very different indications on the PGA distributions. Moreover, PGA values often display significant discrepancy from the macroseismic intensity values calculated with the ESI scale. Therefore, the incorporation of the environmental earth effects into the probabilistic/deterministic hazard analysis appears to be mandatory in order to achieve a more accurate seismic estimation.
Recent and historical studies of earthquake-induced liquefaction, as well as paleoliquefaction studies, demonstrate the potential usefulness of liquefaction data in the assessment of the earthquake potential of seismic sources. Paleoliquefaction studies, along with other paleoseismology studies, supplement historical and instrumental seismicity and provide information about the long-term behavior of earthquake sources. Paleoliquefaction studies focus on soft-sediment deformation features, including sand blows and sand dikes, which result from strong ground shaking. Most paleoliquefaction studies have been conducted in intraplate geologic settings, but a few such studies have been carried out in interplate settings. Paleoliquefaction studies provide information about timing, location, magnitude, and recurrence of large paleoearthquakes, particularly those with moment magnitude, M, greater than 6 during the past 50,000 years. This review paper presents background information on earthquake-induced liquefaction and resulting soft-sediment deformation features that may be preserved in the geologic record, best practices used in paleoliquefaction studies, and application of paleoliquefaction data in earthquake source characterization. The paper concludes with two examples of regional paleoliquefaction studies—in the Charleston seismic zone and the New Madrid seismic zone in the southeastern and central United States, respectively—which contributed to seismic source models used in earthquake hazard assessment.
Large pre-historical earthquakes leave traces in the geological and geomorphological record, such as primary and secondary surface ruptures and mass movements, which are the only means to estimate their magnitudes. These environmental earthquake effects (EEEs) can be calibrated using recent seismic events and the Environmental Seismic Intensity Scale (ESI2007). We apply the ESI2007 scale to the 1992 MS7.3 Suusamyr Earthquake in the Kyrgyz Tien Shan, because similar studies are sparse in that area and geological setting, and because this earthquake was very peculiar in its primary surface rupture pattern. We analyze literature data on primary and secondary earthquake effects and add our own observations from fieldwork. We show that the ESI2007 distribution differs somewhat from traditional intensity assessments (MSK (Medvedev-Sponheuer-Karnik) and MM (Modified Mercalli)), because of the sparse population in the epicentral area and the spatial distribution of primary and secondary EEEs. However, the ESI2007 scale captures a similar overall pattern of the intensity distribution. We then explore how uncertainties in the identification of primary surface ruptures influence the results of the ESI2007 assignment. Our results highlight the applicability of the ESI2007 scale, even in earthquakes with complex and unusual primary surface rupture patterns.
The 2018 M w 6.4 Hualien earthquake struck the eastern Taiwan and caused serious damage. We investigate the rupture properties of the 2018 Hualien earthquake by inverting teleseismic body wave and forward modeling GPS coseismic deformation. The rupture process and slip pattern of preferred model explain both the far-field (teleseismic data) and near-field (GPS) observations. The results show that the 2018 Hualien mainshock ruptured southward on two fault segments, with a weak but fast initiation (3.0 km s-1) in the main west-dipping segment F1 and slow (2.0 km s-1) yet significant slip on shallow east-dipping segment F2. In the past few years, several moderate-sized events, which struck eastern Taiwan and caused strong ground shaking and some seismic damage, are considered occurring on the west-dipping fault. Additional investigations are required to building up the knowledge of this not well-known region.
Uttarakhand Himalayas are highly sensitive to seismic hazard with possible occurrence of high-magnitude earthquakes. Fewer waveforms are available from previously recorded earthquakes, which are insufficient for carrying out seismic hazard studies. The recently installed strong motion instrumentation network (SMIN) in India, particularly, in Indian Himalayas is providing useful data. Using recorded data from SMIN, time-dependent peak ground acceleration and observed peak ground velocity shake maps are drawn for two earthquakes widely recorded by SMIN in Uttarakhand region of Indian Himalayan belt. Open-source Earthworm software with new algorithms is used for drawing these shake maps. The source mechanism is computed for April 4, 2011 earthquake using waveform inversion technique to relate it to the trend of shake maps. The computed focal mechanism shows one of the nodal planes in NW–SE, which are consistent with shake maps for the same earthquake. These time-dependent plotted shake maps provide useful information on the initial rupture, as well as the potential directivity of the rupture.
On February 6, 2018, a ML 6.2 earthquake struck the east coast of Taiwan and caused more than 200 casualties in the Hualien area. The mainshock initiated at a shallow depth of 6.3 km and was accompanied by numbers of foreshocks and aftershocks. Coseismic ruptures widely occurred along the Milun Fault with various deformational structures and caused a variety of damage. Extensive field survey and drone-based images reveal the distribution of offsets and the characteristics of the surface ruptures. The major surface ruptures were mostly synthetic and antithetic Riedel shears interlinked by push-up moletracks or tensional fissures. The strike of the principal displacement zone evolved from northeast to northwest and defined a 7.5-km-long NS fault trace concave to the east. The vertical offset reached its maximum of 50 cm on the north segment and became insignificant toward south. Both on-fault single measurements and cumulative sinistral offsets estimated across the rupture zones showed the pattern of southward declining with the maximum offset of 77 cm in the north. The width of the damage zone increased from 1-20 m to maximum 270 m in the south where the overstepping segments occurred. The development of step-overs is significant in the south, especially in the downtown area where slip is distributed across a transpressional area. Overall, the distinct features of the coseismic ruptures reflect the complex near-surface geology along the Milun Fault and offer new insights for future hazard assessments of the Hualien area.
A deadly Mw 6.4 earthquake occurred in the Hualien area of eastern Taiwan on February 6th, 2018. It caused severe damage to infrastructure and creating surface ruptures in several areas mostly near the Milun Fault in Hualien City. In this study, we investigated the distribution of co-seismic surface ruptures by measuring the orientations of the ruptures, classifying the fracture patterns, and measuring the fracture geometries to calculate the principal displacement zone (PDZ) and the regional stress directions. As a result, local PDZ is observed to rotate anti-clockwise along the Milun Fault from north to south. Considering the deformation behaviors of the fractures and their relative positions along the Milun Fault, the shear zone in Qixingtan area is a horsetail structure derived from the right side of the end of the left-lateral strike-slip fault. In addition, the 170° trending fault splay in the middle segment and the fault branch corresponding to the Beipu Fault are elements of the Riedel shear structure associated with the left-lateral moving Milun Fault. Our results show that Riedel shear structures are common within co-seismic surface rupture zones in this area, and the variations in the orientations of Riedel structures reflect the influence of the pre-existing Milun Fault. We can also determine the most recent geometry, kinematics, anddisplacement characteristics of the Milun Fault through co-seismic surface ruptures and macro-scale Riedel shear structure analysis.This study provides a good example of understanding the relationship between the outcrop scale and the macro-scale of the Riedel shear model.
The February 2018 M w 6.4 earthquake in eastern Taiwan caused extensive damage in Hualien City. Although damaging earthquakes are common in this region, there are relatively few permanent seismic stations deployed. Two days after the mainshock, we deployed 70 temporary seismic stations around Hualien City for 12 days (8–19 February), and station spacing was 1–5 km. During this time, 2192 aftershocks were located from which 580 focal mechanisms were determined. The aftershock sequence extended about 25 km southwestward from the epicenter of the mainshock into the Longitudinal Valley and to depths between 5 and 15 km. Earthquake hypocenters indicate that the aftershocks took place along a near-vertical to steeply west-dipping plane in the north that becomes more diffuse in the south. Focal mechanisms are predominantly extensional, different than the left-lateral strike slip with thrust-component faulting of the mainshock. Very few events occurred in the uppermost crust at depths of less than 5 km, and their focal mechanisms are left-lateral strike-slip faulting. From the mainshock to the aftershocks, the stress changed rapidly from a north-northwest-oriented compressional axis (P axis) to the same direction for the extensional axis (T axis).
On 6 February 2018, an Mw 6.4 earthquake struck near the city of Hualien, in eastern Taiwan with a focal depth of 10.4 km. The earthquake caused strong shaking and severe damage to many buildings in Hualien. The maximum intensity during this earthquake reached VII (>0.4g) in the epicentral region, which is extreme in Taiwan and capable of causing damage in built structures. About 17 people died and approximately 285 were injured. Taiwan was one of the first countries to implement an earthquake early warning (EEW) system that is capable of issuing a warning prior to strong shaking. In addition to the official EEW run by the Central Weather Bureau (CWB), a low‐cost EEW system (P‐alert) has been deployed by National Taiwan University (NTU). The P‐alert network is currently operational and is capable of providing on‐site EEW as well as a map of expected ground shaking. In the present work, we demonstrate the performance of the P‐alert network during the 2018 Hualien earthquake. The shake maps generated by the P‐alert network were available within 2 min and are in good agreement with the patterns of observed damage in the area. These shake maps provide insights into rupture directivity that are crucial for earthquake engineering. During this earthquake, individual P‐alert stations acted as on‐site EEW systems and provided 2–8 s lead time in the blind zone around the epicenter. The coseismic deformation (Cd) is estimated using the records of P‐alert stations. The higher Cd values (Cd>2) in the epicentral region are very helpful for authorities for the purpose of responding to damage mitigation.
The ascending and descending InSAR deformations derived from ALOS-2 and Sentinel-1 satellite SAR images and GPS displacements are used to estimate the fault model of the 2018 Mw 6.4 Hualien earthquake. The sinistral strike-slip fault dipping to the west with a high dip angle of 89.4° and a rake angle of 201.7° is considered as the seismogenic fault of this event. This seismogenic fault also triggered the ruptures of the Milun fault, which dips to the east with a dip angle of ~72°, and an unknown west-dipping fault with a dip angle of 85.2°. Two predicted faulting models indicate that the InSAR deformation fields include more postseismic slip than those of the GPS data. The north segment of the Milun fault and west-dipping fault have been triggered by the rupture of the seismogenic fault, but the postseismic slip occurred only in the south segment of the Milun fault. The InSAR-derived co-seismic and postseismic faulting model suggests that the significant slip concentrates at depths of 2.4–15.0 km of the main fault, 0.0–14.0 km of the Milun fault. Only minor slip is detected on the west-dipping fault. The maximum fault slip of ca. 2.1 m is located at the depth of ca. 2.4 km under the Meilun Tableland. The Coulomb failure stress (CFS) change calculated by the co-seismic and postseismic faulting model shows that there is a significant CFS increase in the east of the south segment of the Milun fault, but few of the aftershocks occur in this area, which indicates a high risk of future seismic hazard.
Starting on the day after the mainshock, we mapped in the field and compiled all the available
observations on earthquake environmental effects (EEEs) caused by the Mw 7.8 subduction
earthquake that hit the coastal region of Ecuador on 16 April 2016 (Pedernales earthquake). These
effects include: i) permanent ground deformation, ii) open cracks, iii) liquefaction, iv) landslides,
and v) tsunami waves. We use these observations to evaluate the macroseismic field of the
Environmental Seismic Intensity - ESI-07 scale and compare our results with published
macroseismic data collected using traditional, damage-based, intensity scales. We found systematic
difference in the assessed earthquake intensity, and in the intensity attenuation with distance. A
comparison of our dataset with macroseismic data of six, instrumental, large subduction
earthquakes occurred between Ecuador and Chile, suggests that for the Pedernales earthquake the
ESI-07 works better in the near field whereas damage-based scales are more reliable in the far
field. Therefore, we generate a single integrated intensity dataset for the Pedernales earthquake,
including data measured with EMS-98, MM and ESI-07 scales. This new integrated macroseismic
field provides reliable and comparable information on the seismogenic source, suggesting that a
similar approach could be successfully applied to refine the source model of past subduction
earthquakes in Ecuador and elsewhere.
In 2013, a new network of broadband seismic stations was deployed in the Caucasus region. Broadband displacement data are inverted for the seismic moment tensor of two medium-sized earthquakes occurring in northeast Georgia (17 September 2013, Mw~5.1) and northern Armenia (26 May 2014, Mw~3.6), respectively. The peak ground velocity (PGV) is estimated for each station that recorded the seismic events. We then construct shake maps for those seismic events. Those time-dependent shake maps can provide not only the information on the initial rupture, the ground response as well as the nature of the soil (soft or stiff), but also the potential directivity of the rupture.The goal of the study is to provide a comprehensive image of the spatial distribution of the PGV in the Caucasus region from small-to-moderate earthquakes, as well as to estimate the rupture directivity for the considered seismic events. Our results demonstrate a good consistency between the source mechanism and the regional tectonics, and a directivity of the rupture perpendicular to the faults.
The aim of this study was to provide a contribution to seismic hazard assessment of the Salento Peninsula (Apulia, southern Italy). It is well known that this area was struck by the February 20, 1743, earthquake (I0 = IX and Mw = 7.1), the strongest seismic event of Salento, that caused the most severe damage in the towns of Nardò (Lecce) and Francavilla Fontana (Brindisi), in the Ionian Islands (Greece) and in the western coast of Albania. It was also widely felt in the western coast of Greece, in Malta Islands, in southern Italy and in some localities of central and northern Italy. Moreover, the area of the Salento Peninsula has also been hit by several low-energy and a few high-energy earthquakes over the last centuries; the instrumental recent seismicity is mainly concentrated in the western sector of the peninsula and in the Otranto Channel. The Salento area has also experienced destructive seismicity of neighboring regions in Italy (the Gargano Promontory in northern Apulia, the Southern Apennines chain, the Calabrian Arc) and in the Balkan Peninsula (Greece and Albania). Accordingly, a critical analysis of several documentary and historical sources, as well as of the geologic–geomorphologic ground effects due to the strong 1743 Salento earthquake, has been carried out by the authors in this paper; the final purpose has been to re-evaluate the 1743 MCS macroseismic intensities and to provide a list of newly classified localities according to the ESI-07 scale on the base of recognized Earthquake Environmental Effects. The result is a quite different damage scenario due to this earthquake that could raise the seismic potential currently recognized for the Salento area, and consequently upgrade the seismic hazard classification of the Salento. Indeed it is important to remind that currently, despite the intense earthquake activity recorded not only in the Otranto Channel, but especially in Greece and Albania, this area is classified in the least dangerous category of the Seismic Classification of the Italian territory (IV category).
On 5 February 2016, a moderate earthquake occurred in southwestern Taiwan with ML 6.4 and a focal depth of 16.7 km. This earthquake caused damage to a few buildings and 117 casualties. A low-cost earthquake early warning (EEW) system (P-alert) is in operation for the purpose of EEWand for providing near-real-time shake maps. During this event, a detailed shaking map was generated by the P-alert system within 2 min after the earthquake occurrence, and the high shaking regions strongly correlated with the locations in which the damage and casualties occurred. In the field, individual P-alert devices also serve as onsite EEW systems using P-wave information. The individual P-alert provided a 4-8 s lead time before the arrival of violent shaking in the damaged regions. For regional EEW, both the Central Weather Bureau (CWB, official agency) and the P-alert system responded very well. Currently, regional warnings in Taiwan are only provided to cities at epicentral distances of 50 km or more by the CWB. For cities within a 50-km epicentral distance, the P-alert system could be useful for providing onsite EEW. The performance of the P-alert network during this earthquake proves the efficiency of this real-time, low-cost network in terms of early warning (regional and onsite), near-realtime shake maps, rapid reports, and strong-motion data for research purposes.
In the last twenty years, the interest of scientific community towards Earthquake Environmental Effects (EEEs)
has progressively increased especially in the frame of INQUA - International Union for Quaternary Research.
In 2007 the ESI 2007 (Environmental Seismic Intensity scale) was published, a new intensity scale based only
on EEEs resulting by a revision process taking about 8 years, and promoted by several geologists, seismologists
and engineers coordinated by Servizio Geologico d’Italia (now ISPRA). The ESI 2007 scale integrates traditional
intensity scales, and allow to define seismic intensity based on the entire scenario of effects.
In 2011 the EEE Catalogue was launched, a web infrastructure realized by ISPRA for data collection of
EEEs induced by recent, historical and paleoearthquakes at global level. Cataloguing and classifying EEEs has
allowed to compare past seismic events and to identify the most vulnerable areas in term of site effect.
Some strong earthquakes occurred in the last years have unfortunately pointed out the primary role played by
geological effects in the scenario of damages, confirming that seismic hazard cannot be evaluated only based on
vibratory ground motion but also on the knowledge about EEEs.
This volume provides the state of knowledge about these topics, with the aim to promote the use of the ESI 2007
intensity scale, that has been translated into ten languages, and the EEE Catalogue, as an helpful tool also for
land planning, especially in high seismic hazard areas
Taiwan is located at an active plate boundary and prone to earthquake hazards. To evaluate the island's seismic risk, the Taiwan Earthquake Model (TEM) project, supported by the Ministry of Sciences and Technology, evaluates earthquake hazard, risk, and related social and economic impact models for Taiwan through multidisciplinary collaboration. One of the major tasks of TEM is to construct a complete and updated seismogenic structure database for Taiwan to assess future seismic hazards. Toward this end, we have combined information from pre-existing databases and data obtained from new analyses to build an updated and digitized three-dimensional seismogenic structure map for Taiwan. Thirty-eight on-land active seismogenic structures are identified. For detailed information of individual structures such as their long-term slip rates and potential recurrence intervals, we collected data from existing publications, as well as calculated from results of our own field surveys and investigations. We hope this updated database would become a significant constraint for seismic hazard assessment calculations in Taiwan, and would provide important information for engineers and hazard mitigation agencies.
In this study, we applied the environmental seismic intensity (ESI-2007)
scale to a major recent Algerian earthquake. The ESI-2007 scale is an effective
tool to assess the seismic hazard and has been applied to onshore
earthquakes. Here we applied the scale to a recent earthquake (Mw 6.8,
2003) that took place offshore in the province of Boumerdès in the north
of Algeria along the boundary between African and Eurasian plates. The
main shock was associated to an unknown submarine structure. No surface
ruptures were observed on the onshore domain, but many earthquake
environmental effects (EEEs) were reported during several field investigations.
In addition to onshore ground effects, this event triggered turbidity
currents responsible for 29 submarine cable breaks. Mapping and describing
coseismic ground effects allowed us to distinguish primary and
secondary effects like coastal uplifts, liquefaction phenomena, tsunami
waves, turbidity currents, cracks, rock falls, slope movements and hydrological
anomalies. Considering the total area affected and the distribution
of ground effects, we suggest intensity X that appears in agreement
with intensity calculated in previous study with the EMS-98 scale. Thus,
this method is validated even in the case of a coastal earthquake, and
could be applied in the future to Algerian historical earthquakes that have
affected scarcely inhabited zones but where EEEs were listed and located.
The main objective of this paper was to introduce the Environmental Seismic Intensity scale (ESI), a new scale developed and tested by an interdisciplinary group of scientists (geologists, geophysicists and seismologists) in the frame of the International Union for Quaternary Research (INQUA) activities, to the widest community of earth scientists and engineers dealing with seismic hazard assessment. This scale defines earthquake intensity by taking into consideration the occurrence, size and areal distribution of earthquake environmental effects (EEE), including surface faulting, tectonic uplift and subsidence, landslides, rock falls, liquefaction, ground collapse and tsunami waves. Indeed, EEEs can significantly improve the evaluation of seismic intensity, which still remains a critical parameter for a realistic seismic hazard assessment, allowing to compare historical and modern earthquakes. Moreover, as shown by recent moderate to large earthquakes, geological effects often cause severe damage”; therefore, their consideration in the earthquake risk scenario is crucial for all stakeholders, especially urban planners, geotechnical and structural engineers, hazard analysts, civil protection agencies and insurance companies. The paper describes background and construction principles of the scale and presents some case studies in different continents and tectonic settings to illustrate its relevant benefits. ESI is normally used together with traditional intensity scales, which, unfortunately, tend to saturate in the highest degrees. In this case and in unpopulated areas, ESI offers a unique way for assessing a reliable earthquake intensity. Finally, yet importantly, the ESI scale also provides a very convenient guideline for the survey of EEEs in earthquake-stricken areas, ensuring they are catalogued in a complete and homogeneous manner.
The early 2014 Cephalonia (Ionian Sea, western Greece) earthquake sequence comprised two main shocks with almost the same magnitude (Mw 6.0) occurring successively in short time (January 26 and February 3) and space (western Cephalonia, Paliki peninsula). Two different almost parallel NE-SW striking and SE dipping at a steep-angle dextral strike-slip fault zones with small reverse component corresponded to the two events and were activated onland in Paliki. Many earthquake environmental effects (EEE) were induced by both earthquakes in Paliki offering the possibility to apply the ESI 2007 scale. They are classified into primary and secondary effects. Primary effects comprise uplift, subsidence and surface ruptures. Secondary effects include ground cracks, slope movements, liquefaction and hydrological anomalies. The VIIIESI2007 intensities are assigned to sites of maximum uplift in the central-eastern part of Paliki. The VIIESI2007 intensities are assigned to sites with maximum subsidence, surface ruptures and large-volume slope movements in the eastern coastal zone of Paliki, the northern part of Paliki and the northern part of Argostoli peninsula, respectively. The VIESI2007 intensities are assigned to sites with ground cracks and slope movements mainly in the northern part of Paliki and the western part of Aenos Mt, respectively. The lowest VESI2007 intensities are observed in the southern part of Paliki associated with small-volume slope movements. From the comparison of all data, it is concluded that there is a strong correlation between the active faults, the displacement discontinuities detected from already published interferometric analysis and the spatial distribution of the EEE.
http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/memorie-descrittive-della-carta-geologica-ditalia/earthquake-environmental-effect-for-seismic-hazard-assessment-the-esi-intensity-scale-and-the-eee-catalogue
In the last twenty years, the interest of scientific community towards Earthquake Environmental Effects (EEEs)
has progressively increased especially in the frame of INQUA - International Union for Quaternary Research.
In 2007 the ESI 2007 (Environmental Seismic Intensity scale) was published, a new intensity scale based only
on EEEs resulting by a revision process taking about 8 years, and promoted by several geologists, seismologistsand engineers coordinated by Servizio Geologico d’Italia (now ISPRA). The ESI 2007 scale integrates traditional intensity scales, and allow to define seismic intensity based on the entire scenario of effects.
In 2011 the EEE Catalogue was launched, a web infrastructure realized by ISPRA for data collection of
EEEs induced by recent, historical and paleoearthquakes at global level. Cataloguing and classifying EEEs has
allowed to compare past seismic events and to identify the most vulnerable areas in term of site effect.
Some strong earthquakes occurred in the last years have unfortunately pointed out the primary role played by
geological effects in the scenario of damages, confirming that seismic hazard cannot be evaluated only based on vibratory ground motion but also on the knowledge about EEEs.
This volume provides the state of knowledge about these topics, with the aim to promote the use of the ESI 2007 intensity scale, that has been translated into ten languages, and the EEE Catalogue, as an helpful tool also for land planning, especially in high seismic hazard areas.
Claudio CAMPOBASSO
Earthquake Environmental Effects (EEEs) such as surface faulting, landslides, liquefaction
and tsunamis are widely distributed following strong seismic events and may account for a significant part of the overall damage. Here, we investigate EEEs generated by two
earthquakes with different source parameters, both occurring along the Mexican subduction zone: the Sept. 8, 2017, Mw 8.2, moderate depth, normal fault, intraslab event; and the June 23, 2020, Mw 7.0, shallow depth, thrust fault, interface event. We document the EEEs for each event, assign an intensity value using the Environmental Seismic Intensity (ESI-2007) scale, and derive the macroseismic fields. Finally, we compute the attenuation of intensity with distance and we compare it with other subduction zone earthquakes worldwide, demonstrating the repeatability of EEEs. This work represents the first application of the ESI-2007 scale to an intraslab earthquake and documents its wide applicability in different seismotectonic settings. We argue that EEEs provide useful information that should not be neglected in seismic hazard assessment procedures
Two earthquakes having almost the same magnitude occurred in the Hualien area of Taiwan in 2018 and 2019. The 2018 earthquake had a magnitude ML 6.2 produced severe destruction; however, the 2019 earthquake (ML=6.3) did not cause any severe damage. The P-Alert Strong Motion Network provides real-time shakemaps, in addition, to earthquake early warning (EEW) in terms of lead-time. Each instrument provides a different lead-time using peak ground acceleration (PGA) and peak ground velocity (PGV). During both the events, the instruments reported a lead-time of 1.5 to 8.0 s in the epicentral region. This network system also generated high-quality shakemaps during both earthquakes. The shakemaps showed that the higher PGAs are concentrated in the epicentral region for the 2018 and 2019 earthquakes. The lower PGA contour (≥ 25 gals) extended to a broader area, including Taipei, during the 2019 earthquake compared to the 2018 earthquake. However, PGV shakemaps display a different pattern. The higher PGV values (more than 17 cm/s) are observed in the epicentral region during the 2018 earthquake (locations suffering building collapse) compared to the 2019 earthquake, suggesting that PGV correlates better with damage distribution as compared to the PGA. The PGV shakemap, currently only available for the P-Alert network, provides crucial information that complements the PGA issued by the official agency in Taiwan.
Earthquakes produce effects on the built and natural environment, the severity of which decays with distance from the epicenter. Empirical relations describing the intensity attenuation with distance are fundamental for seismic hazard assessment and for deriving parameters for preinstrumental events. Seismic intensity is usually assigned based on damage to buildings and infrastructures; this can be challenging for intensity degrees higher than X or when macroseismic fields of multiple events close in time are overlapping. A complementary approach is the study of earthquake environmental effects (EEEs), which are used to assign intensity on the environmental scale intensity (ESI) scale. However, a quantitative comparison between the ESI and traditional scales, and an equation describing the ESI attenuation with distance are still lacking. Here, we analyze 14 historical and instrumental events (time window 1688–2016) in the central and southern Apennines (Italy), comparing ESI and Mercalli–Cancani–Sieberg (MCS) intensities. Our results show that ESI consistently provides higher intensity near the epicenter and the attenuation is steeper than MCS. We derive the first intensity prediction equation for the ESI scale, which computes local intensity as a function of distance and epicentral intensity value. We document that, in the near field, the MCS attenuation for shallow crustal events occurred in the twenty-first century is steeper than previous events, whereas the ESI attenuation shows a consistent behavior through time. This result questions the reliability of current empirical relations for the investigation of future events. We recommend including EEEs in intensity assignments because they can guarantee consistency through time and help in evaluating the spatial and temporal evolution of damage progression during seismic sequences, thus ultimately improving seismic risk assessment.
In the framework of a bilateral cooperation project between the geological surveys of China and Italy, the geological effects of six strong to moderate earthquakes occurred in Sichuan, China (2008, 2013, 2017) and in Central Apennines, Italy (2009, 24 Aug. and 30 Oct 2016) were compared.
The main aim was to test the applicability and effectiveness of the ESI intensity scale in areas characterized by different tectonic settings (compressive and strike-slip vs. extensional), and also by different local conditions (e.g., geomorphologic, lithologic and climatic) that can influence the occurrence and size of individual EEEs at a specific site.
In general, for all these earthquakes the distribution and size of geological effects resulted proportional to the earthquake severity. However, notably, the earthquakes of moderate magnitude (i.e., between 6 and 7) showed i) well evident surface faulting only in the extensional domain of the Central Apennines, while poor or no evidence was found for reverse and strike-slip events (Sichuan); ii) a strong influence on the occurrence of secondary effects from site conditions (e.g., lithology, elevation, slope angle, soil cover, climate), those that typically control for example the susceptibility to landsliding.
Based on the ESI intensity scale, epicentral and local intensities were estimated by means of the surface faulting extent and of the total area of secondary effects, mainly landslides. The comparison with the damage or PGA-based intensities has confirmed the efficacy of the ESI scale to improve the portrait of the earthquake and to pinpoint areas of enhanced hazard, especially those related to slope failures and liquefaction. This work is also a substantial contribution to the future revision of the ESI scale, in particular for reverse faulting earthquakes.
We use high‐resolution Pléiades optical satellite imagery to study the distribution and magnitude of fault slip along the Milun fault surface rupture, which broke during the 2018 Hualien earthquake ( Mw 6.4) in eastern Taiwan. Correlation of pre‐ and postearthquake stereo Pléiades images reveals detailed 3D surface displacements along the 8‐km‐long Milun fault, with maximum ∼1 m left‐lateral offsets across the fault. Along the northern section of the Milun fault, our correlation results indicate a localized deformation zone, with offset values slightly larger than the maximum offsets reported in the field ( ∼77 cm ). To the south, the left‐lateral offsets become increasingly distributed, producing arctangent shapes in displacement profiles crossing the fault. In places, the deformation zone reaches widths of 200+m and can be explained by a shallow east‐dipping fault rupture extending from 2 to 3 km depth to 70–120 m below the surface. A very shallow coseismic rupture on the Milun fault is consistent with a shallow locking depth interpreted from previous geodetic analyses from the interseismic period. Despite a few highly discontinuous and irregular surface ruptures reported along the southern section of the fault, our results suggest the main fault slip (up to 1 m) stopped at very shallow depths below the surface, in which ∼60% of the deformation may be accommodated as off‐fault deformation (OFD). In this upper ∼100 m of the crust, OFD may be promoted by a significant change in material strength, as the fault crosses from bedrock and/or consolidated sediments into weaker, water‐rich, poorly consolidated alluvial sediments.
Soil liquefaction and ground settlements during an earthquake of M L 6.2 that took place on 6 February 2018 in Hualien, Taiwan are presented in this article based on the results of a field reconnaissance that focused on geotechnical aspects. Cracks of road pavement with sand eruption were found in a former wetland. Slight settlement of several residential buildings that are located near the Meilun River was observed. In addition, minor sand boils and lateral spreading occurred at the riverbanks of the Meilun and Hualien Rivers. In general, liquefaction and ground settlements in Hualien City were sparse and localized in weak ground, causing no damage to structures and facilities. However, in the Port of Hualien, ground settlements up to 50–60 cm, as well as considerable pavement cracks, were induced in the backland of several gravity-type wharves, especially those in the jetty area. Many of the cracks and settlements were accompanied by eruption of the mixture of sand and gravel with a maximum grain size up to 10 cm. These phenomena were due to the liquefaction of the backfill material. Fortunately, there was only scarcely noticeable tilt and structural damage of the caisson quay walls and scarce settlement of the apron. Thus, the serviceability of these wharves was not greatly influenced.
The P-alert seismic network, an on-site low-cost earthquake early warning system (EEWS) located in Taiwan, has proven useful in earthquake events since 2010. This dense network can produce detailed shakemaps and identify the direction of the source rupture in near-real time. Based on real-time acceleration signals and the proposed time-dependent anisotropic attenuation relationship with peak ground acceleration (PGA), ShakingAlarm, a regional early warning system add-on to the original P-alert network, can immediately provide (1) an accurate predicted PGA, before the arrival of the observed PGA, that will give a consistent lead time for hazard assessment and emergency response, (2) a predicted shakemap (PSM) that will converge faster to the final reported shakemap than the regional EEWS, and (3) a shake contour area-based magnitude estimation that is robust, even in the absence of a measured shake contour area such as in the case of an offshore earthquake. Taking the 2016 Mw 6.4 Meinong earthquake as an example, the 14th second PSM from Shaking-Alarm converges on the final shakemap better than the regional EEWS from the Central Weather Bureau (CWB) in Taiwan. According to our tests, ShakingAlarm provides a warning using modified Mercalli intensity (MMI) V that is consistent with the results of another on-site EEWS (Strategies and Tools for Real Time Earthquake Risk ReducTion [REAKT]). Further performance tests were conducted with another five ML > 5:5 inland earthquakes from 2013 to 2014. Compared with traditional regional EEWSs, ShakingAlarm can effectively identify possible damage regions and provide valuable early warning information (PSM, predicted PGA, and magnitude) for risk mitigation.
The Environmental Seismic Intensity (ESI) scale has been officially released in 2007 and is based on the quantification of Earthquake Environmental Effects. Due to its quantitative nature, the scale improves the process of assessing macroseismic intensities, particularly in the epicentral area of those cases in which sole traditional intensity scales prove to be ineffective. Following a large number of publications that applied this relatively newly established scale, there is some need for parametrization. This is because this intensity scale can offer new insights to seismic hazard assessment and has the potential to reduce the uncertainties that stem from traditional macroseismic scales. This study has three main goals. Firstly, to enrich and compile an ESI 2007 database from earthquakes in Greece by adding 4 new events. Secondly, to extract a relationship between Magnitude and the ESI 2007 for Greece and the Mediterranean. Thirdly, to offer a preliminary estimate of how the intensity attenuates with distance, after developing a code in Python language to assist this process. The ESI 2007 scale was applied in the 1995 Ms = 6.6 Kozani-Grevena earthquake, the 1978 Mw = 6.5 Thessaloniki earthquake, the historic 1894 Atalanti earthquake sequence (M = 6.4 and M = 6.8) and the 365AD event in Crete (M = 8.4). These events were selected because they have well documented and extensive co-seismic effects, including primary and secondary surface ruptures, rockfalls, landslides and liquefaction phenomena. For the Kozani earthquake, extracted results were correlated with SAR interferograms, in order to provide a complete and high spatial resolution of the ground deformation. Both the Kozani-Grevena and the Thessaloniki events produced a maximum intensity IX on the ESI 2007 scale, the Atalanti earthquake produced a maximum intensity X and the 365AD Crete earthquake a maximum intensity XII. Overall, the ESI 2007 scale compares fairly well with the traditional macroseismic scales except for some villages in the Kozani-Grevena epicentral area where due to the poor quality of buildings, existing scales overestimated the intensity by one degree compared to the ESI 2007. It is interesting to note that both for Greece and the Mediterranean area a strong correlation exists between Mw and the ESI 2007 scale. In particular, the following relationships between the Mw and the ESI scale have been extracted: i) for Greece Io(ESI 2007) = 3.1427 exp (0.1643Mw) and ii) for the Mediterranean Io(ESI 2007) = 3.3543exp (0.1557Mw).
This work presents high-resolution ShakeMaps for three earthquakes occurred in the Betic Cordillera (SE Spain): the 2011 CE Lorca event (VIII ESI-07), the 1863 CE Huercal-Overa event (VIII ESI-07) and the 1829 CE Torrevieja event (X ESI-07). Detailed field characterizations and mapping of their coseismic environmental effects (EEEs) are catalogued and classified following the ESI-07 scale. The resulting macroseismic information reaches up to ten times the existing information based on conventional damagebased scales (e.g. EMS-98), providing a better constrain towards more realistic ground-motion scenarios.
The 2011 Lorca earthquake has been used as a calibration event, since there is a relevant record of instrumental measures on source, and ground-motion parameters allowing a direct comparison with the modelled PGA values. From a methodological standpoint, the obtained ShakeMaps follow the basic guidelines and methodology proposed by the USGS ShakeMap Program. The two historical earthquakes analysed in this paper produced a wide variety of secondary EEEs but no surface faulting was reported. These effects need to be properly identified by high-resolution DTMs (5 m/pixel), far from the c. 900 m/pixel terrain models used by USGS program. Additionally, the proposed ESI-07 ShakeMaps incorporate correction factors to solve inconsistencies derived from the large scale terrain models considered in standard USGS program workflows: (1) empirical slope-derived Vs 30 models result in overestimations of the PGA values in flat terrains in absence of unconsolidated deposits; (2) the topographic amplification factor included here, explains the occurrence of rock-falls and landslides in steep areas, where ground motion is underestimated by the sole use of slope-derived Vs 30 models. Basic geological and geomorphological information need to be implemented in the modelling workflow in both cases. To prevent PGA overestimations in flat terrains a correction factor related to the spatial distribution and thickness of the Quaternary unconsolidated deposits has been incorporated (i.e. isopach maps). To correct PGA underestimations in steep terrains an amplification factor was modelled following standard guidelines of seismic topographic amplification.
The comparison via iteration of the spatial distribution of both ESI effects and EMS macroseismic data, with the obtained ground-motion spatial distribution, enables a better definition of the geological parameters for the studied historical earthquakes. A more accurate location and/or size of the suspect seismic sources are obtained for these historical earthquakes, providing scenarios more realistic than those resulting from old intensity maps. Quaternary Geology and Geomorphology are behind the implementation of the proposed ESI-07 ShakeMaps, being especially useful when exploring historic or ancient moderate earthquakes with scarce damage-based macroseismic data, but with sufficient paleoseismic or archaeoseismic records. In summary, the methodological workflow proposed here contemplates the implementation of a computational configuration seismologically relevant and able to test repeated seismic scenarios, with different parametric data, in a controlled GIS environment useful to reproduce historical events.
On November 17, 2015 a strong, shallow earthquake (Mw = 6.5) occurred on the island of Lefkada along a N20 ± 5°E, east-dipping strike-slip fault with right-lateral sense of slip. The event triggered environmental effects that were mainly mapped at the western part of the island while moving towards the eastern part, the severity of the earthquake-induced failures decreased. The most characteristic geological effects that were triggered by the earthquake were slope failures including rock falls, rock slides and landslides. The spatial density of the failures follows an exponential increase with slope-angle and decreases for values larger than 55°. Small-size liquefaction phenomena such as sand craters and ejection of fine-grained sand through ground cracks were documented at the coastal area of Vassiliki. The epicentral intensity was assessed based on the definitions of Environment Seismic Intensity scale as VIII ESI-07, and the macroseismic epicenter (VIII up to IX) was located at the coastal area of Egremnoi (west of Athani village, south Lefkada).
On January 26th and February 3rd, 2014, two earthquakes occurred onshore the island of Cephalonia inducing severe environmental effects. The main types of earthquake-induced failures were liquefaction and slope failures and were mainly widespread at the western and central part of the island at Paliki peninsula. Although the fact that the generated strong motions by the second event were the highest ever recorded in Greece, medium severity structural damages were induced. Few days after the occurrence of the events, two post-earthquake field surveys took place in order to document the generated environmental effects. By taking into account these field observations, it was decided to evaluate the macroseismic intensity of the February 3rd, 2014 earthquake by applying the ESI-07 scale. As an outcome, the epicentral intensity of Feb. 3rd, 2014 was evaluated as VII ESI-07 by taking into account the total affected area. Furthermore, as it is pointed out in primary contemporary sources and seismic catalogues, similar environmental failures such as liquefaction phenomena at coastal areas and large scale rockfalls were triggered by historical earthquakes at the island of Cephalonia. The most accurately described effects are the ones triggered by the 1867 earthquake. Therefore, it was decided to assess the macroseismic intensities of this historical event based on the ESI-07 scale and compare it with the relevant ones of Feb 3rd, 2014 event. As an outcome, it is concluded that similar intensities were assessed for both events, VIII ESI-07 for 1867 event and VII ESI-07 for the February 2014 one, despite the fact that the relevant earthquake magnitudes strongly differ. Outlining the results of this study, it is reconfirmed the importance of the recording and documentation of earthquake environmental effects in order to maintain the consistency with the historical earthquake catalogues. Moreover, a re-evaluation of historical earthquake magnitudes at the area of Cephalonia island could be realized in order to accurately update the seismic hazard.
Application of the ESI 2007 Scale is implemented by compilation of reports and quantification of the surface effects on the geological environment (i.e., length and width of ground fractures, width of lateral spreading, diameter of mud/sand/gravel boils) during two recent large earthquakes: South Island, New Zealand (3 September 2010 Mw 7.1, referred to here as the New Zealand earthquake [NZE]) and Tohoku, Japan (11 March 2011 Mw 9.0, referred to here as the Japan earthquake [JPE]). These two earthquakes occurred on different types of faults and in different geological and tectonic settings: the NPE was oblique to the Alpine fault, a strike‐slip fault segment that is part of the tectonics between the Australian and Pacific plates that involves compressional regime and dextral component of motion, and the JPE occurred along the subduction zone between the Pacific and Okhotsk plates at the latitude of the Japan trench. From secondary information mined from various sources (including reports of reconnaissance campaigns, published papers, satellite imagery and photographs, and local reports from the affected areas), a database was compiled containing surface environmental effects of the two earthquakes to determine intensity levels and to construct preliminary isoseismal maps. In the case of NZE, intensities reached degree XI and reports were concentrated in the surroundings of the Christchurch district, whereas, in the case of JPE, reports were distributed along the Tohoku and Kanto regions in northeastern Honshu and intensities reached degree XII. The isoseismal maps constructed based solely on the environmental effects are a good complement to other estimates of intensity for both earthquakes.
The 1999 Chi-Chi, Taiwan, earthquake caused many fatalities and much economic loss for people living in the central part of the island. It also provided many valuable lessons for mitigating future earthquake loss. In this article we have analyzed the human-fatality data from the earthquake in terms of spatial distribution and age dependence to reach the following conclusions. First, rupturing of the Chelungpu fault definitively influenced the spatial distribution of fatalities. Ground ruptures caused by unusually large thrust and left-lateral displacement of the east-dipping fault resulted in almost total destruction of structures on the hanging-wall block along the 100-km-long fault zone. Patterns of damaging ground motion were highly asymmetric about the fault trace. High ground accelerations above 400 gal resulted in high fatality rates up to 1.112% in the sparsely populated rural areas east of the fault. Fortunately, the densely populated urban areas west of the fault suffered substantially lower fatality rates below 0.002% due to low ground accelerations significantly below 400 gal. Secondly, clear age dependence of the human-fatality rate was found from demographic data of the two hardest-hit Nantou and Taichung counties. Results for both counties define almost identical functions that shows people older than age 40 are increasingly more vulnerable with increasing age to life loss in earthquakes. These two conclusions can be applied to make a reliable estimation of the total human fatalities in areas of high seismic intensity either before a large earthquake by performing scenario studies, or shortly after a real earthquake by a system of rapid intensity mapping. Finally, empirical time functions of the cumulative numbers of people found killed, injured, and missing during the first hours following the Kobe, Japan, and Chi-Chi, Taiwan, earthquakes both show that search and rescue operations were critical in the first 48 hr.
The epicenter of the Taitung Earthquake of November 24, 1951 has been relocated much closer to the trajectory of surface faulting and within the area of maximum seismic intensity. Analysis of first motion data and the dislocation of surface faulting suggests that the Taitung Earthquake occurred on an oblique left-lateral strike-slip with a convergent component. This is consistent with the observations of geodesy and field geology. It is also noted that the principal compressional axes were oriented in a NW-SE direction, which agrees with the direction of regional tectonic stress.
Data were collected from 281 Taiwan continuous Global Positioning System (cGPS) Array sites from 2007-2013 and processed with GAMIT/GLOBK software. Power spectral density stacking from cGPS position time series in Taiwan found the spectral index as -0.72, -0.77, and -0.57 for the E, N, U components, respectively. This indicates the cGPS data errors can be described as a combination of white noise and flicker noise. The common-mode errors are removed by stacking data from 50 cGPS sites with data periods greater than 5 years. By removing the common-mode errors the GPS data precision is further improved to 2.3, 1.9, and 6.9 mm in the E, N, U components, respectively. After strict data quality control, time series analysis and noise analysis, we derive a new Taiwan velocity field using cGPS data from 2007-2013. The general pattern of the newly derived 2007-2013 velocity field is quite similar to that from previous studies, but the station density is much larger and spatial coverage better. About 80 mm yr-1 plate convergence rate is observed, half of the rate is accommodated on the fold and thrust belt of western Taiwan and another half is taken up in the Longitudinal Valley and Coastal Range in eastern Taiwan. The velocities in western Taiwan generally show a fan-shaped pattern, consistent with the maximum compression tectonic stress direction. In northern Taiwan the velocity vectors reveal clockwise rotation, indicating the on-going extensional deformation related to the back-arc extension of the Okinawa Trough. In southern Taiwan, the horizontal velocity increases from about 40 mm yr-1 in the Chia-Nan area to 55 mm yr-1 in the Kao-Ping area with a counterclockwise rotation.