Exploring the knowledge domain of earthquake prediction based on bibliometric analysis and text mining

Earthquake prediction is one of the important themes of earthquake research, and it is also a very difficult scientific problem in the world. In this study, a bibliometric analysis is conducted on the scientific publications about earthquake prediction indexed in SCIE (Science Citation Index Expanded) and SSCI (Social Sciences Citation Index) databases during the past two decades (1998–2017). The subject categories, annual and journal distributions, leading countries/regions and institutions are investigated in this field. The main research topics are identified through text mining method. The research trends are explored by keyword co-occurrence analysis and bursting keywords detection techniques. The results of this study are helpful for scholars in this field to find the knowledge structure and important participants. It is also helpful for scholars to seize the current research hotspots and future development trends in this field.

KOERI’s Tsunami Warning System in the Eastern Mediterranean and Its Connected Seas: A Decade of Achievements and Challenges

A tsunami warning system providing services in the Eastern Mediterranean, Aegean, Marmara and Black Seas under the UNESCO Intergovernmental Oceanographic Commission (IOC)—Intergovernmental Coordination Group (ICG) for the Tsunami Early Warning and Mitigation System in the North-Eastern Atlantic, the Mediterranean and Connected Seas (NEAMTWS) framework was established in Turkey by the Kandilli Observatory and Earthquake Research Institute (KOERI) (Özel et al., 2011). KOERI’s Regional Earthquake and Tsunami Monitoring Center (RETMC) was established on the foundations of the legacy KOERI National Earthquake Monitoring Center (NEMC) by adding observation, analysis and operational capability related to tsunami early warnings after an extensive preparatory period during 2009 and 2011. The center initiated its test-mode 7/24 operational status as a national tsunami warning center in 2011, and after a one year period it became operational as a candidate tsunami warning center for NEAMTWS on 1 July 2012, together with CENALT (Centre d’Alerte aux Tsunamis—France) and followed by the NOA (National Observatory of Athens—Greece) on 28 August 2012, INGV (Instituto Nazionale di Geofisica e Vulcanologia—Italy) on 1 October 2014 and IPMA (Instituto Português do Mar e da Atmosfera—Portugal) on 1 February 2018, completing full coverage of the tsunami-prone regions monitored by NEAMTWS. In this paper, an overview of the progress and continuous improvement of KOERI’s tsunami early warning system will be presented, together with lessons learned from important tsunamigenic events, such as the 20 July 2017 Bodrum–Kos Mw 6.6 and 30 October 2020 Samos–Izmir Mw 6.9 earthquakes. Gaps preventing the completion of an effective tsunami warning cycle and areas for future improvement are also addressed.

Inhomogeneous precursor characteristics of rock with prefabricated cracks before fracture and its implication for earthquake monitoring

Earthquake precursors and earthquake monitoring are always important in the earthquake research field, even if there is still debate about the existence of earthquake precursors. However, it is extremely difficult to observe the seismogenic environment of earthquakes directly. Laboratory rupture experiment is a useful technique to simulate and gain an insight into the complex mechanisms of earthquakes. Five marble samples with prefabricated cracks are used for uniaxial loading experiments to investigate whether there is a precursory signal before rock fracture and to simulate the rupture process of strike-slip fault. The existence of a precursory signal is confirmed by the coefficient of variation (CV) results, from which we can see two patterns which are known as seismicity acceleration and quiescence before an earthquake. Moreover, these CV findings are applied to determine the locations of large deformation sampling points on the rock surface at different loading stages. Similar results are obtained when we consider actual seismicity at the northern end of the San Andreas Fault in California, which provides crucial evidence to prove the existence of precursor characteristics. In this case, three kinds of seismic monitoring models are designed to find out how to monitor these characteristics more effectively.

An Overview of Earthquake Science in Malaysia

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

Geodetic Investigation of the 30 October 2020 Mw 6.9 Samos-Izmir Earthquake

<p>The earthquake with a magnitude of Mw 6.9 (according to Kandilli Observatory and Earthquake Research Institute-KOERI) occurred 8 km north of Samos Island at a depth of 16 km, on 30.10.2020, at 11:51:24 UTC. It took place on the north-dipping normal fault zone of approximately 40 km length in the sea between Samos Island of Greece and Kuşadası Bay of Turkey. After the mainshock, a tsunami with the height exceeding 1 meter occurred in Seferihisar region, south of Izmir, and north side of Samos Island. In this study, a geodetic investigation of the Samos-Izmir earthquake using GNSS and SAR techniques was carried out. Within the scope of this study, 1Hz observations of Turkey National Continuous GNSS Network-Active (TUSAGA-Aktif) stations in the earthquake zone, were used, and it was aimed to reveal the co-seismic deformation caused by the earthquake. In addition to GNSS data, the InSAR process has been performed by using ESA Sentinel-1 SAR data, and the vertical deformations were clarified with the unwrapped interferogram. The GNSS data were processed using web-based online processing services according to the relative and absolute positioning techniques as static and kinematic modes. In conclusion, considering the absolute and relative static processing of pre- and post-earthquake GNSS data, the maximum horizontal deformations were observed at CESM and IZMI GNSS stations located in the north of the fault. Due to the earthquake, these points moved to the north direction and the maximum horizontal deformations were found as 5.5 cm and 3.5 cm, respectively. According to the kinematic processing of the GNSS data, instantaneous horizontal movements of 12 cm and 4 cm towards the north were observed at the same stations, respectively, at the time of the earthquake. On the contrary, DIDI and AYD1 GNSS stations, which are located in the south of the fault, moved to the south-east direction and the magnitude of horizontal deformations were smaller. Considering the InSAR results, it was seen a 10 cm uplift in the west of the island of Samos and a 10 cm subsidence at the northernmost part. Besides this, a 5 cm subsidence was observed in Izmir territory, the north side of the fault, by means of the interferogram.</p>

Ray paths of VLF/LF transmitter radio signals in the seismic Adriatic regions

<p>We analyze the radio wave propagations of VLF/LF transmitter signals along subionospheric paths using two different reception systems localized in the Graz seismo-electromagnetic facility (15.43E,47.06N). Those systems allow the simultaneous detection of more than fifteen transmitter signals emitting in the northern (i.e. France, Germany and United Kingdom) and southern (i.e. Italy and Turkey) parts of Europe. In this work, we investigate the transmitter radio wave propagations associated with two earthquakes (EQs) which occurred, at two occasions, in nearly the same Croatian regions (Geo. Long.=16°E; Geo. Lat.=45°N). The first and second EQs happened, respectively, on March 22 and December 29, 2020, with magnitudes M<sub>w</sub> equal to 5.4 and 6.4. The use of two complementary reception systems, i.e. INFREP (Biagi et al., Open Journal of Earthquake Research, 8, 2019) and UltraMSK (Schwingenschuh et al., Nat. Hazards Earth Syst. Sci., 11, 2011), and the proximity to the epicenters lead us to characterize the behavior of the transmitter signal amplitudes particularly above the Croatian seismic regions. We analyze the amplitude variation for a given transmitter frequency starting few weeks before the earthquakes occurrences. We discuss the observed anomalies in the transmitter signals which may be considered as precursors due to the ionospheric disturbances of the transmitter ray paths above the earthquakes preparation zones. </p>

A possible radio anomaly observed on the occasion of the MW=6.0 earthquake occurred in Dodecanese islands at the end of January 2020

<p>Since 2009, several VLF/LF radio receivers have been installed throughout Europe in order to realize a European radio network for studying the radio precursors of earthquakes, called the INFREP network. The current network has nine VLF/LF receiving stations, two in Romania and<br>Greece, one in Italy, Austria, Portugal, Cyprus, and Serbia. The receivers can measure with 1 min sampling rate the intensity of 10 radio signals in the band VLF (10-50 kHz) and LF (150-300 kHz). The scope of existing transmitters is manifold, e.g. they are used for radio broadcast (LF), for radio-navigation or time signals and mainly for military purposes in the VLF range. At the end of January 2020 an intense seismic crisis occurred in Dodecanese Islands; the main event (Mw= 6.0) occurred on January 30. This seismic activity occurred in the "sensitive" area of the INFREP network. The analysis of the data collected by INFREP receivers has revealed clear anomalies in three VLF signals appearing some days before the main earthquake. The anomalies appear in the trends collected by the Cyprus receiver and the epicenter is inside the 5<sup>th</sup> Fresnel ellipses defined by transmitters-receiver. Here we report the data analysis and we present in detail the anomalies. The possibility that they are precursors of the quoted earthquake seems significant.</p><p>Biagi, P.F., Colella, R., Schiavulli, L., Ermini, A., Boudjada, M., Eichelberger, H., Schwingenschuh, K., Katzis, K., Contadakis, M.E., Skeberis, C., Moldovan, I.A. and Bezzeghoud, M. (2019) The INFREP Network: Present Situation and Recent Results. Open Journal of Earthquake Research,8, 101-115. https://doi.org/10.4236/ojer.2019.82007</p>