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.

A sismicidade no Curso de Sismologia (1970) de Frederico Machado e seis cartas históricas de isossistas com interesse para o Ensino de Ciências

Resumo Nos documentos curriculares portugueses em vigor para a disciplina de Ciências Naturais, 7.o ano de escolaridade, há uma orientação no sentido da exploração e discussão de cartas de isossistas relativas a sismos com efeitos no território nacional. Neste trabalho incluímos alguns apontamentos históricos sobre o conceito de intensidade sísmica, a qual permite a medição de um terramoto sem recurso a instrumentos, e apresentamos seis cartas de isossistas que constam no Curso de Sismologia (1970) de Frederico Machado. Para cada carta de isossistas analisámos as fontes utilizadas pelo autor e produzimos uma reflexão com sugestões para exploração em contexto didático. Verificámos que estas cartas são representativas da sismicidade no território português e constituem uma oportunidade para explorar o conceito de intensidade sísmica e corresponder às orientações curriculares (ensino básico) para este tema. Palavras-chave: História da Sismologia, intensidade sísmica, cartas de isossistas Abstract In current portuguese curricular documents for the Natural Sciences subject, 7th grade, there is an orientation towards exploring and discussing isoseismal maps related to earthquakes with effects in the portuguese territory. In this work we include some historical notes about the concept of seismic intensity, which allows the measurement of an earthquake without the use of instruments, and we present six isoseismals maps that are included in Curso de Sismologia (1970) by Frederico Machado. For each isoseismal map we analyzed the sources used by the author and we produced a reflection with suggestions for didactic exploration. We found that these maps are representative of the seismicity in the Portuguese territory and provide an opportunity to explore the concept of seismic intensity and to meet the curricular orientations (basic education) for this theme. Keywords: History of Seismology, seismic intensity, isoseismal maps

DEVELOPING SEISMIC INTENSITY MAPS FROM TWITTER DATA; THE CASE STUDY OF LESVOS, GREECE 2017 EARTHQUAKE: ASSESSMENTS, IMPROVEMENTS AND ENRICHMENTS ON THE METHODOLOGY

<p><strong>Abstract.</strong> This article presents an effort to validate and further improve a previously published innovative approach for drawing macroseismic intensity maps from data extracted from sources of volunteered geographic information (VGI). Our approach involves classification of macroseismic observations (extracted from social media sources) to values of the EMS 98 intensity scale, leading to the drawing of isoseismal maps. The earthquake of June 12th, 2017 (Mw 6.3) that occurred off the south coast of Lesvos Island, Greece, was used as a case study; its main shock was located at depth of about 13&amp;thinsp;km. This specific event, which claimed the life of a woman and caused at least 15 injuries due to collapsing buildings and falling debris (mainly in the town of Vrissa), was chosen for the specific geomorphological characteristics of the meizoseismal area, time of occurrence and distribution of damage. Twitter was chosen as a VGI source mostly for reasons of consistency with the original published work, generating comparable findings that can be assessed more readily to facilitate further development of the methodology. Results of the dataset analysis include the drawing of the isoseismal maps from Tweets published within different time periods (6&amp;thinsp;h, 12&amp;thinsp;h, 24&amp;thinsp;h, 48&amp;thinsp;h); and the identification of various text patterns regarding the evaluation of the macroseismic observations that result into intensity values. The present work offers additional empirical evidence regarding the validity of the methodology presented in the scientific literature, and further enriches it by providing additional text patterns and specific improvements related to the classification of the information in certain values of seismic intensity. Assessment of the results is enriched by the progress that has been noted in the field and has been presented in the international scientific literature since 2016.</p>

California earthquake history

This paper presents an overview of the advancement in our knowledge of California's earthquake history since ~ 1800, and especially during the last 30 years. We first review the basic statewide research on earthquake occurrences that was published from 1928 through 2002, to show how the current catalogs and their levels of completeness have evolved with time. Then we review some of the significant new results in specific regions of California, and some of what remains to be done. Since 1850, 167 potentially damaging earthquakes of M ~ 6 or larger have been identified in California and its border regions, indicating an average rate of 1.1 such events per year. Table I lists the earthquakes of M ~ 6 to 6.5 that were also destructive since 1812 in California and its border regions, indicating an average rate of one such event every ~ 5 years. Many of these occurred before 1932 when epicenters and magnitudes started to be determined routinely using seismographs in California. The number of these early earthquakes is probably incomplete in sparsely populated remote parts of California before ~ 1870. For example, 6 of the 7 pre-1873 events in table I are of M = 7, suggesting that other earthquakes of M 6.5 to 6.9 occurred but were not properly identified, or were not destructive. The epicenters and magnitudes (M) of the pre-instrumental earthquakes were determined from isoseismal maps that were based on the Modified Mercalli Intensity of shaking (MMI) at the communities that reported feeling the earthquakes. The epicenters were estimated to be in the regions of most intense shaking, and values of M were estimated from the extent of the areas shaken at various MMI levels. MMI VII or greater shaking is the threshold of damage to weak buildings. Certain areas in the regions of Los Angeles, San Francisco, and Eureka were each shaken repeatedly at MMI VII or greater at least six times since ~ 1812, as depicted by Toppozada and Branum (2002, fig. 19).