EPS Excellent Paper Award

The 2021 EPS Excellent Paper Award is granted to the paper by Christopher C. Finlay, Clemens Kloss, Nils Olsen, Magnus D. Hammer, Lars Tøffner-Clausen, Alexander Grayver and Alexey Kuvshinov (2020).

The CHAOS‑7 geomagnetic field model and observed changes in the South Atlantic Anomaly   
Christopher C. Finlay, Clemens Kloss, Nils Olsen, Magnus D. Hammer, Lars Tøffner-Clausen, Alexander Grayver & Alexey Kuvshinov 
Earth, Planets and Space volume 72, Article number: 156  (2020)

The Earth’s magnetic field controls the flux of charged energetic particles into the atmosphere. Notably in the area of the so-called South Atlantic anomaly (SAA) the magnetic field is weak allowing for increased particle flux which is sensed by the electronics of passing satellite, e.g. in form of so-called single event upsets. Thus, the SAA is not only an interesting phenomenon in space, but also significant for space flight and possibly connected to operation failures.

CHAOS-7 is the time-dependent near-Earth geomagnetic field model spanning 1999–2020. It includes a time-dependent internal field up to spherical harmonic degree 20, a static internal field for degree 21 and larger, which is merged to another crustal field model at degree 25, and a model of the magnetospheric field with its induced counterpart. A major improvement compared with CHAOS-6 is use of additional data from the on-going Swarm and CryoSat-2 missions, stricter criteria for selecting geomagnetically quiet times, spherical harmonic expansion to higher degree for a time-dependent internal field, and relaxation of the temporal regularization at higher degrees, resulting in lower residuals between the model field and observations. The CHAOS-7 model is used to study the recent outstanding issue about evolution of the SAA. Clearly detected is the expansion of the weakest magnetic field over central South America and the development of a distinct secondary minimum around southwest of Africa. It is concluded that these are respectively due to the gathering of reversed flux patches under South America and the westward movement of an intense reversed flux below South Africa at the core-mantle boundary. CHAOS-7 is also useful to discover localized changes in radial field acceleration between 2015 and 2018 in the central and western Pacific. This paper significantly contributes to the geomagnetic field modeling by providing the CHAOS model and has been highly cited. In addition to updating the model, it investigates the cause of the two exceptional phenomena related to the geomagnetic field evolution. Therefore, the 2021 EPS Excellent Paper Award is given to this paper.

The 2020 EPS Excellent Paper Award goes to the authors of the following paper:

Understanding and forecasting phreatic eruptions driven by magmatic degassing
John Stix and J. Maarten de Moor
Earth, Planets and Space 70, Article number: 83 (2018)

A critically important question during phreatic explosions caused by rapid heating and vaporization of groundwater are determining if magma is involved or not. Through an integration of observation of different volcanoes, Stix and de Moor (2018) defined the two endmember types of phreatic eruptions driven by inputs of magma and magmatic gas: (1) type 1, in which magmatic contributions into an overlying and variably sealed hydrothermal system result in overpressure; (2) type 2, whereby the magmatic inputs vaporize confined near-surface liquid water, causing overpressure The authors demonstrated a number of geophysical as well as geochemical precursory signals are useful in understanding and forecasting phreatic eruptions. Therefore, this paper significantly contributes not only to better understand the phreatic eruptions but also to mitigate volcanic hazards through multidisciplinary monitoring.

The 2019 EPS Excellent Paper Award is granted to the paper by Satoshi Fujiwara, Hiroshi Yarai, Tomokazu Kobayashi, Yu Morishita, Takayuki Nakano, Basara Miyahara, Hiroyuki Nakai, Yuji Miura, Haruka Ueshiba, Yasuaki Kakiage and Hiroshi Une (2016)

Small-displacement linear surface ruptures of the 2016 Kumamoto earthquake sequence detected by ALOS-2 SAR interferometry
Satoshi Fujiwara, Hiroshi Yarai, Tomokazu Kobayashi, Yu Morishita, Takayuki Nakano, Basara Miyahara, Hiroyuki Nakai, Yuji Miura, Haruka Ueshiba, Yasuaki Kakiage & Hiroshi Une
Earth, Planets and Space volume 68, Article number: 160 (2016)

The 2016 Kumamoto earthquake sequence began with an initial earthquake of a moment magnitude (Mw) 6.2 on April 14 (JST), followed by the mainshock with Mw 7.0 on April 16; it lasted for more than a month accompanied by numerous aftershocks. While those earthquakes occurred around the previously mapped active faults, the Futagawa and Hinagu fault zones in central Kyushu, it is important to clarify if and to what extent the associated co- and post-seismic surface displacements were attributable to them. Using satellite radar interferometry (InSAR) images of the Advanced Land Observing Satellite2, Fujiwara et al. (2016) detected approximately 230 linear surface ruptures with small displacements, most of which were outside the main faults and probably triggered by the main earthquake and aftershocks. The detailed images demonstrated the power of InSAR for deformation mapping and contributed to our understanding of the generation of surface faults. Therefore, this paper significantly contributes not only to the advancement of our knowledge of earthquake rupture processes but also to the assessment of the future possible seismic hazards.

The 2018 EPS Excellent Paper Award is granted to the paper by Aitaro Kato, Toshiko Terakawa, Yoshiko Yamanaka, Yuta Maeda, Shinichiro  Horikawa, Kenjiro Matsuhiro and Takashi Okuda (2015).

Preparatory and precursory processes leading up to the 2014 phreatic eruption of Mount Ontake, Japan 
Aitaro Kato, Toshiko Terakawa, Yoshiko Yamanaka, Yuta Maeda, Shinichiro  Horikawa, Kenjiro Matsuhiro, Takashi Okuda

A phreatic eruption occurred at Mount Ontake on September 27, 2014, causing the highest number of casualties among Japanese volcanic disasters seen in recent decades. The mechanisms of phreatic eruptions, in comparison to magmatic eruptions, are not well understood and are difficult to predict because they tend to occur at shallow depths without any clear precursors. Kato et al (2015) revealed detailed seismicity migrations prior to, and during, the eruptions by relocating volcano tectonic events and long period events. Evidence of fluid migrations under the volcano were strongly implicated by the spatio-temporal distribution of these earthquakes and the temporal variations of b-values. The volcano-seismology data clearly demonstrated the preparatory and precursory stages of phreatic eruptions; therefore, the paper significantly contributes to the advancement of our knowledge of phreatic eruption processes.

The 2017 EPS Excellent Paper Award is granted to the paper by Yoshifumi Saito, Masaki N. Nishino, Masaki Fujimoto, Tadateru Yamamoto,Shoichiro Yokota, Hideo Tsunakawa, Hidetoshi Shibuya, Masaki Matsushima, Hisayoshi Shimizu, Futoshi Takahashi (2012).

Simultaneous observation of the electron acceleration and ion deceleration over lunar magnetic anomalies
Yoshifumi Saito, Masaki N. Nishino, Masaki Fujimoto, Tadateru Yamamoto,Shoichiro Yokota, Hideo Tsunakawa, Hidetoshi Shibuya, Masaki Matsushima, Hisayoshi Shimizu, Futoshi Takahashi

To understand the interaction between solar wind and lunar magnetic anomalies, low energy electrons and ions over lunar magnetic anomalies were simultaneously observed for the first time by the "Kaguya" satellite. This paper discusses the plasma structure over the mini-magnetosphere. The observations clearly showed acceleration of electrons and deceleration of ions and suggested the existence of a non-adiabatic dissipative interaction between solar wind ions and lunar magnetic anomalies. Since the interaction between solar wind and lunar magnetic anomalies occurs on the smallest scale of its kind, it contributes to the understanding of the interaction between solar wind and magnetized airless bodies in space. This is one of the most significant achievements of the Japanese spacecraft mission "Kaguya". These observations have been cited by many studies dealing with solar wind-lunar magnetic anomalies interactions.

The 2016 EPS Excellent Paper Award is granted to the paper by Yushiro Fujii, Kenji Satake, Shin'ichi Sakai, Masanao Shinohara, and Toshihiko Kanazawa (2011).

Tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake
Yushiro Fujii, Kenji Satake, Shin’ichi Sakai, Masanao Shinohara, and Toshihiko Kanazawa

This paper compiled the Tsunami waveform data from tide gauges, GPS wave gauges, and ocean bottom pressure gauges associated with the 2011 Tohoku Earthquake. From the waveform inversion, the authors successfully explained the two-step waveforms, which were the most outstanding characters of the data. First, to explain the initial rise in water level, the slip on the plate interface was estimated at the southern Sanriku and Miyagi-oki, around the epicenter. Second, to explain the later impulsive waveform, a large slip of around 40 m was modeled along the trench axis. This timely publication, as a contribution to the special issue of “First Results of the 2011 Off the Pacific Coast of Tohoku Earthquake”, provided a standard model for the study of the 2011 Tohoku earthquake. As such, this paper has received a large number of citations and is therefore well-deserved of the EPS Excellent Paper Award 2016.