Felt Earthquakes Research Articles

Phenological and seismological impacts on airborne pollen types: A case study of Olea pollen in the Region of Murcia, Mediterranean Spanish climate

The rationale of this paper was to investigate whether earthquakes impact airborne pollen concentrations, considering some meteorological parameters. Atmospheric pollen concentrations in the Region of Murcia Aerobiological Network (Spain) were studied in relation to the occurrence of earthquakes of moment magnitude (up to Mw = 5.1) and intensity (intensity up to grade VII on the European Macroseismic Scale). In this study, a decade (2010–2019) was considered across the cities of the network. Earthquakes were detected in 12 out of 1535 days in the Olea Main Pollen Season in Cartagena, 49 out of 1481 days in the Olea Main Pollen Season in Lorca, and 39 out of 1441 days in the Olea Main Pollen Season in Murcia. The Olea pollen grains in this network were attributed to the species Olea europaea, i.e., the olive tree, a taxon that appears widely in the Mediterranean basin, in both cultivated and wild subspecies. Differences between the Olea concentration on days with and without earthquakes were only found in Lorca (Kruskal-Wallis: p-value = 0.026). The low frequency and intensity of the earthquakes explained these results. The most catastrophic earthquake felt in Lorca on May 11th, 2011 (IVII, Mw = 5.1, 9 casualties) did not result in clear variations in pollen concentrations, while meteorology (e.g., African Dust Outbreak) might have conditioned these pollen concentrations. The research should be broadened to other active seismological areas to reinforce the hypothesis of seismological impact on airborne pollen concentrations.

EARTHQUAKES FELT in MOLDOVA in 2015: January, 24 with КP=12.2, Mw=4.3; March, 16 with КR=11.6, Mw=4.3 and March, 29 with КR=11.9, Mw=4.5 (Romania–Moldova)

All earthquakes felt in 2015 on the territory of Moldova occurred outside its borders, in the Vrancea and Pre-Carpathian regions (Romania). In 2015, the population of Moldova felt 4 earthquakes: on January 19 and 24, on March 16 and 29. The article discusses in detail the three most powerful of them – January 24, March 16, and 29 with epicenters in the Vrancea mountain range. The January 24 earthquake with Mw=4.3 and hрР=89 km was felt in Romania and the Republic of Moldova, where it was observed with the intensity I=3 in Cahul and I=2 in Chisinau. The March 16 earthquake with Mw=4.3 and hрР=121 km was felt in the eastern and southern counties of Romania (8 settlements). It was observed on the territory of the Republic of Moldova with the intensity I=3 in Cahul and I=2–3 in Chisinau. The intensity in the epicenter did not exceed I=4. The March 29 earthquake with Mw=4.5 and hрР=144 km was felt in the eastern and southern counties of Romania (8 settlements). It was observed on the territory of the Republic of Moldova with intensity I=3–4 in Cahul and I=2–3 in Chisinau. Solutions of the focal mechanism based on data from various agencies are presented. All three earthquakes occurred under the influence of the prevailing near-horizontal compression stress. The study is carried out within the framework of the State program, Geoseism project, registration number 36/21.10.19А.

Contributed Reports of Widely Felt Earthquakes in California, United States: If They Felt it, Did They Report it?

In a recent study,Hough and Martin(2021) considered the extent to which socioeconomic factors influence the numbers and distribution of contributed reports available to characterize the effects of both historical and recent large earthquakes. In this study I explore the question further, focusing on analysis of widely felt earthquakes near major population centers in northern and southern California since 2002. For most of these earthquakes there is a correlation between average household income in a postal ZIP code and the population-normalized rate of responses to the DYFI system. As past studies have demonstrated, there is also a strong correlation between DYFI participation and the severity of shaking. This first-order correlation can obscure correlations with other factors that influence participation. Focusing on five earthquakes between 2011 and 2021 that generated especially uniform shaking across the greater Los Angeles, California, region, response rate varies by two orders of magnitude across the region, with a clear correlation with demographics, and consistent spatial patterns in response rate for earthquakes 10 years apart. While there is no evidence that uneven DYFI participation in California impacts significantly the reliability of intensity data collected, the results reveal that DYFI participation is significantly higher in affluent parts of southern California compared to economically disadvantaged areas.

Recent felt earthquakes (Mw 5.0–5.9) in Mizoram of north‐east India region: Seismotectonics and precursor appraisal

Eight medium magnitude (Mw 5.0–5.9) severely felt earthquakes, mostly at a shallower depth (<35 km), occurred in a short period of 7 months only, April–October, 2020, in Mizoram State, north‐east region (NER) of India, and it created much panic in the state. The increasing population growth as well as rapid urbanization in Aizawl, the capital city of Mizoram, may be under severe threat for an impending large earthquake in the region. The NER, India, is jawed between two arcs, the Himalayan Arc collision zone to the north and the Indo–Burma (Myanmar) Arc subduction zone to the east, and witnessed two great earthquakes (Mw ≥ 8.0, 1897 and 1950) and a total of 25 large earthquakes (Mw ≥ 7.0) in the past since 1869. The 2020 sudden burst of seismic activity in Mizoram, along with a strong (Mw 6.7) earthquake in Manipur in 2016 and a medium magnitude (Mw 5.7) earthquake in 2017 in Tripura, adjacent to the Mizoram State, are critically examined to understand the ongoing seismotectonics and the precursor implications, if any. The 2016 Manipur earthquake is interpreted to be an intra‐plate earthquake triggered by the transverse Kopili Fault by strike‐slip motion. The 2017 Tripura earthquake is also interpreted to be typically an intra‐plate strike‐slip event in the eastern margin of the Bengal Basin. The seismic activity in Mizoram, on the other hand, is found to have occurred in the accretionary Indo–Burma Wedge, between the Churachandpur Mao Fault and Eastern Boundary Thrust. The centroid moment tensor solutions of the events suggest the dextral‐slip motion of the wedge along the Indo–Burma Arc. A preliminary analysis of the Mizoram seismicity recognizes a precursor anomaly, a temporal variation of much higher seismic activity, for an impending large earthquake in the study area.

Mayotte seismic crisis: building knowledge in near real-time by combining land and ocean-bottom seismometers, first results

SUMMARYThe brutal onset of seismicity offshore Mayotte island North of the Mozambique Channel, Indian Ocean, that occurred in May 2018 caught the population, authorities and scientific community off guard. Around 20 potentially felt earthquakes were recorded in the first 5 d, up to magnitude Mw 5.9. The scientific community had little pre-existing knowledge of the seismic activity in the region due to poor seismic network coverage. During 2018 and 2019, the MAYOBS/REVOSIMA seismology group was progressively built between four French research institutions to improve instrumentation and data sets to monitor what we know now as an on-going exceptional submarine basaltic eruption. After the addition of 3 medium-band stations on Mayotte island and 1 on Grande Glorieuse island in early 2019, the data recovered from the Ocean Bottom Seismometers were regularly processed by the group to improve the location of the earthquakes detected daily by the land network. We first built a new local 1-D velocity model and established specific data processing procedures. The local 1.66 low VP/VS ratio we estimated is compatible with a volcanic island context. We manually picked about 125 000 P and S phases on land and sea bottom stations to locate more than 5000 events between February 2019 and May 2020. The earthquakes outline two separate seismic clusters offshore that we named Proximal and Distal. The Proximal cluster, located 10 km offshore Mayotte eastern coastlines, is 20–50 km deep and has a cylindrical shape. The Distal cluster start 5 km to the east of the Proximal cluster and extends below Mayotte's new volcanic edifice, from 50 to 25 km depth. The two clusters appear seismically separated, however our data set is insufficient to firmly demonstrate this.

When Punjab Cried Wolf: How a Rumor Triggered an “Earthquake” in India

Abstract In recent years, earthquake felt reports contributed via online systems have provided increasingly valuable sources of data to characterize earthquakes and their effects. Contributed felt reports are accompanied by increases in website traffic, which are themselves potentially useful for the early detection of seismic events. In February 2017 the European-Mediterranean Seismic Centre detected an unusual surge in traffic from the Punjab region in northwestern India, although no nearby seismic event was detected instrumentally. Had crowdsourcing detected a felt earthquake that instruments had missed? Or did Punjab cry wolf? In this Earthquake Lites report, we describe the sleuthing endeavor undertaken to find an answer.

Evaluation of geohazards in the Cape Girardeau area using LiDAR and GIS, Southeast Missouri, USA

The New Madrid Seismic Zone (NMSZ) has historically recorded some of the largest intensity earthquakes in North America, including significant earth movements that resulted in about 2000 felt earthquakes during 1811–1812. The region continues to experience mass wasting due to earth movements. The aim of this study is to understand the influence of geologic variables on mass wasting processes in the greater Cape Girardeau area, which forms the commercial center of Missouri's fertile "Bootheel" region. Earth movement susceptibility was evaluated in Cape Girardeau and Bollinger counties and portions of Stoddard and Scott counties by mapping potential landslide features on topographic maps, field verification of such features, and geospatial analysis of recent LiDAR imagery. In order to evaluate the changes in surface morphology, slope inclination, hillshade aspect, hydrology, lithology, faults, precipitation, seismicity, sinkholes, and geohydrology were considered. Geographically weighted analysis of the geomorphologic variables identified zones of relative risk. In addition, data were evaluated for oil and gas pipelines, bridges, utilities, and open pit mines associated with mass wasting on public and economic infrastructure. The results suggest that anthropogenic changes commonly associated with urban development impact land use, runoff, infiltration, and slope failures, while sustained precipitation and seismic ground shaking tend to trigger landslides. The scale of mass wasting in the study area was robust, varying from as small as one-half hectare to as much as 67 km2. The vulnerability of the population in susceptible areas tends to increase at the lower elevations and on alluvial flood plains. Thus, hazard susceptibility evaluation can be useful in both community planning as well as emergency preparedness.

The unusual case of the ultra-deep 2015 Ogasawara earthquake (MW7.9): Natural time analysis

On 30 May 2015, a powerful earthquake (EQ) (M W 7.9, Japan Meteorological Agency reported magnitude M8.1) struck west of Japan's remote Ogasawara (Bonin) island chain, which lies more than 800 km south of Tokyo. It occurred at 680 km depth in an area without any known historical seismicity. It was the first EQ felt in every Japanese prefecture since intensity observations began in 1884. Here, by applying natural time analysis, which unveils hidden properties in complex time series, we find that almost three and a half months before this powerful EQ, which is the strongest one after the M W 9.0 Tohoku EQ on 11 March 2011, the fluctuations of the order parameter of seismicity were minimized around 17 February 2015. Remarkably, such a behavior has been also observed 1–3 months before all shallow EQs in Japan of magnitude M7.6 or larger that occurred since 1984 until the M W 9.0 Tohoku EQ. We also find that upon the Ogasawara EQ occurrence the change of the entropy of Japanese seismicity upon changing the direction of the time arrow (i.e., under time reversal) exhibited a minimum. This minimum, which may appear when a system approaches a dynamic phase transition, is not equally deep with that observed on 22 December 2010 along with the occurrence of a M7.8 EQ in Bonin islands. The fact that the latter EQ was followed almost 3 months later by the appreciably stronger Tohoku EQ, while the Ogasawara EQ did not, is discussed in the frame of the Lifshitz-Slyozov-Wagner theory of phase transitions and subsequent work by Penrose and coworkers.

Exploiting Real-time Search Engine Queries for Earthquake Detection: A Summary of Results

Online search engine has been widely regarded as the most convenient approach for information acquisition. Indeed, the intensive information-seeking behaviors of search engine users make it possible to exploit search engine queries as effective “crowd sensors” for event monitoring. While some researchers have investigated the feasibility of using search engine queries for coarse-grained event analysis, the capability of search engine queries for real-time event detection has been largely neglected. To this end, in this article, we introduce a large-scale and systematic study on exploiting real-time search engine queries for outbreak event detection, with a focus on earthquake rapid reporting. In particular, we propose a realistic system of real-time earthquake detection through monitoring millions of queries related to earthquakes from a dominant online search engine in China. Specifically, we first investigate a large set of queries for selecting the representative queries that are highly correlated with the outbreak of earthquakes. Then, based on the real-time streams of selected queries, we design a novel machine learning–enhanced two-stage burst detection approach for detecting earthquake events. Meanwhile, the location of an earthquake epicenter can be accurately estimated based on the spatial-temporal distribution of search engine queries. Finally, through the extensive comparison with earthquake catalogs from China Earthquake Networks Center, 2015, the detection precision of our system can achieve 87.9%, and the accuracy of location estimation (province level) is 95.7%. In particular, 50% of successfully detected results can be found within 62 s after earthquake, and 50% of successful locations can be found within 25.5 km of seismic epicenter. Our system also found more than 23.3% extra earthquakes that were felt by people but not publicly released, 12.1% earthquake-like special outbreaks, and meanwhile, revealed many interesting findings, such as the typical query patterns of earthquake rumor and regular memorial events. Based on these results, our system can timely feed back information to the search engine users according to various cases and accelerate the information release of felt earthquakes.

Study of Characteristics of Fault Slip and Induced Seismicity during Hydraulic Fracturing in HDR Geothermal Exploitation in the Yishu Fault Zone in China

Hot dry rock (HDR) geothermal energy has become promising resources for relieving the energy crisis and global warming. The exploitation of HDR geothermal energy usually needs an enhanced geothermal system (EGS) with artificial fracture networks by hydraulic fracturing. Fault reactivation and seismicity induced by hydraulic fracturing raise a great challenge. In this paper, we investigated the characteristics of fault slip and seismicity by numerical simulation. The study was based on a hydraulic fracturing project in the geothermal field of Yishu fault zone in China. It revealed that fluid injection during hydraulic fracturing can cause the faults that exist beyond the fluid-pressurized region to slip and can even induce large seismic event. It was easier to cause felt earthquakes when hydraulic fracturing was carried out in different layers simultaneously. We also examined the effects of the location, permeability, and area of the fracturing region on fault slip and magnitude of the resulting events. The results of the study can provide some useful references for establishing HDR EGS in Yishu fault zone.

Stress-Drop Estimates for Induced Seismic Events in the Fort Worth Basin, Texas

ABSTRACTEarthquakes in the Fort Worth basin (FWB) have been induced by the disposal of recovered wastewater associated with extraction of unconventional gas since 2008. Four of the larger felt earthquakes, each on different faults, prompted deployment of local distance seismic stations and recordings from these four sequences are used to estimate the kinematic source characteristics. Source spectra and the associated source parameters, including corner frequency, seismic moment, and stress drop, are estimated using a modified generalized inversion technique (GIT). As an assessment of the validity of the modified GIT approach, corner frequencies and stress drops from the GIT are compared to estimates using the traditional empirical Green’s function (EGF) method for 14 target events. For these events, corner-frequency residuals (GIT−EGF) have a mean of −0.31 Hz, with a standard deviation of 1.30 Hz. We find consistent mean stress drops using the GIT and EGF methods, 9.56 and 11.50 MPa, respectively, for the common set of target events. The GIT mean stress drop for all 79 earthquakes is 5.33 MPa, similar to estimates for global intraplate earthquakes (1–10 MPa) as well as other estimates for induced earthquakes near the study area (1.7–9.5 MPa). Stress drops exhibit no spatial or temporal correlations or depth dependency. In addition, there are no time or space correlations between estimated FWB stress drops and modeled pore-pressure perturbations. We conclude that induced earthquakes in the FWB occurring on normal faults in the crystalline basement release pre-existing tectonic stresses and that stress drops on the four sequences targeted in this study do not directly reflect perturbations in pore-fluid pressure on the fault.

Is an Earthquake Felt Inside a Car?

AbstractThe analysis of how an earthquake is felt was addressed with the data provided by citizens through a website dedicated to the perception of earthquakes in Italy (Data and Resources). The analysis focused on the perception of earthquakes by observers inside both parked and moving cars. These situations were compared with outdoor ones. The felt percentage of each situation was quantified for epicentral distance ranges and European Macroseismic Scale (EMS) degree. One of the main findings was the greatest sensitivity to shaking for people inside parked cars due to resonance phenomena of the automobile–observer system. The distribution of the intensity of perception in the car was analyzed as a function of the hypocentral distance and the magnitude of the earthquake. It was possible to define the attenuation trends of these intensities. The comparison of these trends with those of the equations for estimation of response spectral ordinates allowed us to have an evaluation of the frequency values of the seismic waves that caused the vibrations felt, which were found to agree with the typical frequencies of the car–observer system, as highlighted by independent studies. The results of this analysis show the possibility to include the perception of the earthquake inside a parked and moving car among the diagnostics used in the definition of macroseismic intensity degree of the EMS.

Quantifying nuisance ground motion thresholds for induced earthquakes

Hazards from induced earthquakes are a growing concern with a need for effective management. One aspect of that concern is the “nuisance” from unexpected ground motions, which have the potential to cause public alarm and discontent. In this article, we borrow earthquake engineering concepts to quantify the chance of building damage states and adapt them to quantify felt thresholds for induced earthquakes in the Central and Eastern United States. We compare binary data of felt or not-felt reports from the “Did You Feel It” database with ShakeMap ground motion intensity measures (IM) for ∼360 earthquakes. We use a Monte Carlo logistic regression to discern the likelihood of perceiving various degrees of felt intensity, given a particular IM. These best-fit nuisance functions are reported in this article and are readily transferable. Of the shaking types considered, we find that peak ground velocity tends to be the best predictor of a felt earthquake. We also find that felt thresholds tended to decrease with increasing earthquake magnitude, after M ∼3.9. We interpret this effect as related to the duration of the event, where events smaller than M 3.9 are perceived as “impulsive” to the human senses. Improved quantification of the nuisance from induced earthquake ground motions could be utilized in management of the public perception of their causal operations. Although aimed at anthropogenic earthquakes, thresholds we derive could be useful in other realms, such as establishing best practices and protocols for earthquake early warning.

Earthquake relocation to understand the megathrust segments along the Sumatran subduction zone

Historical seismicity shows the presence of mega-thrust segments along the Sumatran subduction zone that could generate large earthquakes. The segments include the Aceh-Andaman, Nias-Seumeuleu, Batu, Siberut, Mentawai-Pagai, Enggano, and Sunda Strait. Shallow and large earthquakes with magnitudes larger than 7.5 can occur along the segments thus trigger tsunamis. The accurate seismicity distribution along the subduction zone can be used to characterize the segments. The objective of the research is to precisely relocate the earthquakes in order to investigate the properties of the Sumatran subduction zone. Among more than 5000 preliminary located earthquakes occurring in 1980-2018 obtained from the Indonesian Agency for Geophysics (BMKG), only earthquakes with azimuthal gap angle less than 180 and recorded by at least 4 stations are used in the data analysis. We applied double difference method in order to relocate the seismic events. The result shows a zone with significantly less earthquakes along the subduction in West Aceh interpreted as a seismic gap zone. This zone is expected to accumulate energy which could be released in the form of a large earthquake. The new earthquake locations mimic shallower Sumatran subduction zone further north therefore closer to people inland. The closer earthquake the higher intensity of an earthquake felt by people which higher level of hazard. The pattern of the subduction zone derived from the relocated seismicity can be used as better source information for tsunami modeling.

EARTHQUAKES FELT IN MOLDOVA 2014: March, 29 with КP=12.5, Mw=4.7, September, 10 with КP=12.4, Mw=4.5 and November 22 with КP=14.3, Mw=5.8 (Romania–Moldova)

All earthquakes felt in 2014 on the territory of Moldova occurred outside its borders, in the Vrancea and Pre-Carpathian regions (Romania). In 2014, the population of Moldova felt 13 earthquakes. The article discusses in detail the most powerful events, occurred on March 29, September 6, and November 22. The March 29 earthquake, Mw=4.7, hрР=136 km was felt in the eastern and southern counties of Romania (in 41 settlements), in the Odessa region of Ukraine, and also in the central and southern regions of the Republic of Moldova (22 points). The epicenter was situated in a bend of the Vrancea mountains. The earthquake on Sep-tember 10, Mw=4.5, hрР=108 km was felt in the eastern and southern counties of Romania (in 27 settlements), in the central and southern parts of Moldova (22 points), in the north of Bulgaria and in the Odessa region of Ukraine. Both earthquakes, March 29 and September 10, occurred under the action of prevailing near-horizontal compressive stress. The November 22 earthquake, Mw=5.8, hрР=37 km occurred in the southwestern part of Romania and turned out to be the most significant crust event for the instrumental observation period. Movement in the source occurred under the action of tensile stresses. Earthquakes in this zone continued until January 19, 2015. The largest aftershock was on December 7 with МwMED=4.4. Foci are associated with the activation of the Peceneaga-Camena fault. The main shock was felt in Romania (in 66 settlements) and neighboring countries: Bulgaria, Moldova (23 settlements), Ukraine (18 settlements). The isoseismal maps were constructed for all three earthquakes considered in detail in this work. The intensity at the epicenter of the November 22 earthquake reached I0=6, for other two events I0=5.

Historical and Modern Seismicity of the Semipalatinsk Test Site

According to the current maps of general seismic zoning of the Republic of Kazakhstan (2006), the territory of the Semipalatinsk Test Site (STS) is considered an aseismic region. However, recent investigations and an analysis of archived data have shown that the Test Site territory and its vicinity have experienced and still experience tectonic and induced earthquakes. The maximum magnitude of recorded earthquakes is 5–5.9. An analysis of global seismological bulletins and data on historical seismicity from literature sources is performed to solve the problem of seismicity in the STS region. Historic analog seismograms of earthquakes have been collected since 1925; the earthquake parameters are estimated more precisely. Modern instrumental seismic data of the Kazakhstan monitoring network since 1994 are processed, as is the data of temporary networks of seismic stations operating on the territory of the test site in 2005–2010 in the region of the Sary-Uzen, Balapan, and Degelen test sites. These works resulted in the creation of a common earthquake catalogue for the STS territory and its vicinity from 1783 up to the present. Macroseismic data of the felt earthquakes have been collected; strong motion records have been analyzed. Deep faults dividing Earth’s crust blocks have been marked out. Tectonic elements are located by decoding the Landsat space images and using materials of geologic and topographic surveys. The calculations show that the STS territory can experience events with intensity 6 based on the MSK-64 scale.

High-Resolution Imaging of the ML 2.9 August 2019 Earthquake in Lancashire, United Kingdom, Induced by Hydraulic Fracturing during Preston New Road PNR-2 Operations

AbstractHydraulic fracturing (HF) at Preston New Road (PNR), Lancashire, United Kingdom, in August 2019, induced a number of felt earthquakes. The largest event (ML 2.9) occurred on 26 August 2019, approximately three days after HF operations at the site had stopped. Following this, in November 2019, the United Kingdom Government announced a moratorium on HF for shale gas in England. Here we provide an analysis of the microseismic observations made during this case of HF-induced fault activation. More than 55,000 microseismic events were detected during operations using a downhole array, the vast majority measuring less than Mw 0. Event locations revealed the growth of hydraulic fractures and their interaction with several preexisting structures. The spatiotemporal distribution of events suggests that a hydraulic pathway was created between the injection points and a nearby northwest–southeast-striking fault, on which the largest events occurred. The aftershocks of the ML 2.9 event clearly delineate the rupture plane, with their spatial distribution forming a halo of activity around the mainshock rupture area. Across clusters of events, the magnitude distributions are distinctly bimodal, with a lower Gutenberg–Richter b-value for events above Mw 0, suggesting a break in scaling between events associated with hydraulic fracture propagation, and events associated with activation of the fault. This poses a challenge for mitigation strategies that rely on extrapolating microseismicity observed during injection to forecast future behavior. The activated fault was well oriented for failure in the regional stress field, significantly more so than the fault activated during previous operations at PNR in 2018. The differing orientations within the stress field likely explain why this PNR-2 fault produced larger events compared with the 2018 sequence, despite receiving a smaller volume of injected fluid. This indicates that fault orientation and in situ stress conditions play a key role in controlling the severity of seismicity induced by HF.

Analysis of H/V Ratio Curve to Estimate Seismic Hazard Vulnerability in Lombok Island, West Nusa Tenggara, Indonesia


 
 
 In 2018, Lombok Island was hit by a series of destructive earthquakes. According to Indonesian Meteo- rological, Climatological, and Geophysical Agency data, about 1,973 felt earthquakes (M > 3) which shaken Lombok were recorded during August 2018 with three earthquakes with the largest magnitude of 6.9 Mw, 6.8 Mw, and 6.2 Mw. National Board for Disaster Management reported about 555 deaths, 1,833 people injured, and 186,010 houses damaged as a result of Lombok earthquake on August 5th, 2018. A number of seismometers were placed on Lombok Island from August 3rd, 2018 to October 19th, 2018 to monitor the aftershock events. There are 17 stations that record seismicity in Lombok consisting of 10 broadband sensors and 7 short period sensors. In this study, we used the Horizontal-to-Vertical Spectral Ratio (HVSR) method to analyze the risk of earthquake in the Lombok region. The basic concept of this method is to do a comparison between the horizontal component spectrum and the vertical component spectrum of a wave, where theoretically the particle movement of the horizontal component is greater than the particle movement of the vertical component on soft ground, whereas on the hard ground both components (horizontal and vertical) will be similar. H/V curve obtained from earthquake record- ings (Earthquake Horizontal-to-Vertical Ratio/EHVR) and H/V curve obtained from microtremor recordings (Microtremor Horizontal-to-Vertical Ratio/MHVR) shows good agreement and high correlation. Empirical correction of EMR (Earthquake-to-Microtremor Ratio) managed to decrease the difference of estimation of predominant frequency and amplification factor between EHVR and MHVR. Predominant frequency, amplification, and seismic vulnerability map agree with the geological condition of Lombok Island, where high value of amplification and seismic vulnerability was found on soft and thick ground. This study conclude that the maximum ground acceleration and the construction of the building should also considered when one wants to investigate the effect of an earthquake to the damage occurred, beside the site effects. 
 
 

Accurate Locations of Felt Earthquakes Using Crowdsource Detections

We present a methodology that uses crowdsource detections as an initial location to obtain fast and reliable hypocenter parameters of felt earthquakes using arrival-time data from the GEOFON Program. We derive selection criteria using a 3-year-long training set from the trial runs at the European-Mediterranean Seismological Centre (EMSC) to identify accurate event locations at a high confidence level. Since an event may have several crowd-sourced detections, we also develop a methodology dealing with multiple triggers. We validate the selection criteria using real-time processing of recent data and demonstrate that 95% of the selected events are within 50 km distance from the traditional seismic location published by the EMSC. We show that our methodology provides accurate locations much faster than those published by conventional seismic methods. On average, the EMSC CsLoc service can provide rapid and accurate locations within a minute after the occurrence of a felt earthquake.

Accurate Locations of Felt Earthquakes Using Crowdsource Detections

Accurate Locations of Felt Earthquakes Using Crowdsource Detections