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Dive into the research topics where A. Christophersen is active.

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Featured researches published by A. Christophersen.


Seismological Research Letters | 2016

Comment on “Revisiting the 1894 Omori Aftershock Dataset with the Stretched Exponential Function” by A. Mignan

S. Hainzl; A. Christophersen

ABSTRACT Mignan (2016) claimed that a stretched exponential function describes Omori’s original aftershock data of the 1891 Great Nobi earthquake better than the well‐known Omori law, which is a power law. Besides his preference for the stretched exponential function based on general physical reasoning, he proposed that the Omori law does not hold when the proper visualization method is used; that is, the complementary cumulative density function (CCDF) in a log–log plot. However, his proposed plot is misleading, because it compares data of a finite observation interval with functions integrated over infinite periods. Using the same data as Mignan (2016), we find that an appropriate comparison leads to visually indistinguishable fits for this dataset. The Omori law is preferred based on maximum‐likelihood values. Moreover, the extrapolation shows that it also fits the long‐term data until the centennial anniversary of the Nobi event significantly better than the stretched exponential.


Seismological Research Letters | 2018

The forecasting skill of physics-based seismicity models during the 2010-2012 Canterbury, New Zealand, earthquake sequence

Camilla Cattania; M. Werner; Warner Marzocchi; Sebastian Hainzl; David A. Rhoades; Matthew C. Gerstenberger; Maria Liukis; William Savran; A. Christophersen; Agnès Helmstetter; Abigail Jiménez; Sandy Steacy; Thomas H. Jordan

1 The static Coulomb stress hypothesis is a widely known physical mechanism for 2 earthquake triggering, and thus a prime candidate for physics-based Operational Earth3 quake Forecasting (OEF). However, the forecast skill of Coulomb-based seismicity mod4 els remains controversial, especially in comparison to empirical statistical models. A 5 previous evaluation by the Collaboratory for the Study of Earthquake Predictabil6 ity (CSEP) concluded that a suite of Coulomb-based seismicity models were less in7 formative than empirical models during the aftershock sequence of the 1992 Mw7.3 8 Landers, California, earthquake. Recently, a new generation of Coulomb-based and 9 Coulomb/statistical hybrid models were developed that account better for uncertainties 10 and secondary stress sources. Here, we report on the performance of this new suite of 11 models in comparison to empirical Epidemic Type Aftershock Sequences (ETAS) mod12 els during the 2010-2012 Canterbury, New Zealand, earthquake sequence. Comprising 13 the 2010 M7.1 Darfield earthquake and three subsequent M ≥ 5.9 shocks (including 14 the February 2011 Christchurch earthquake), this sequence provides a wealth of data 15 (394 M ≥ 3.95 shocks). We assessed models over multiple forecast horizons (1-day, 16 1-month and 1-year, updated after M ≥ 5.9 shocks). The results demonstrate substan17 tial improvements in the Coulomb-based models. Purely physics-based models have a 18 performance comparable to the ETAS model, and the two Coulomb/statistical hybrids 19 perform better or as well as the corresponding statistical model. On the other hand, 20 an ETAS model with anisotropic (fault-based) aftershock zones is just as informative. 21 These results provide encouraging evidence for the predictive power of Coulomb-based 22 models. To assist with model development, we identify discrepancies between forecasts 23 and observations. 24


Frontiers of Earth Science in China | 2017

Conceptual Development of a National Volcanic Hazard Model for New Zealand

Mark W. Stirling; Mark Bebbington; Marco Brenna; Shane J. Cronin; A. Christophersen; Natalia Irma Deligne; Tony Hurst; Art Jolly; Gill Jolly; Ben Kennedy; Gábor Kereszturi; Jan M. Lindsay; Vince Neall; Jonathan Procter; David A. Rhoades; Brad Scott; Phil Shane; Ian Smith; Richard Smith; Ting Wang; James D. L. White; Colin J. N. Wilson; Thomas Wilson

We provide a synthesis of a workshop held in February 2016 to define the goals, challenges and next steps for developing a national probabilistic volcanic hazard model for New Zealand. The workshop involved volcanologists, statisticians, and hazards scientists from GNS Science, Massey University, University of Otago, Victoria University of Wellington, University of Auckland, and University of Canterbury. We also outline key activities that will develop the model components, define procedures for periodic update of the model, and effectively articulate the model to end-users and stakeholders. The development of a National Volcanic Hazard Model is a formidable task that will require long-term stability in terms of team effort, collaboration and resources. Development of the model in stages or editions that are modular will make the process a manageable one that progressively incorporates additional volcanic hazards over time, and additional functionalities (e.g. short-term forecasting). The first edition is likely to be limited to updating and incorporating existing ashfall hazard models, with the other hazards associated with lahar, pyroclastic density currents, lava flow, ballistics, debris avalanche, and gases/aerosols being considered in subsequent updates.


Acta Geophysica | 2011

Efficient testing of earthquake forecasting models

David A. Rhoades; Danijel Schorlemmer; Matthew C. Gerstenberger; A. Christophersen; J. Douglas Zechar; Masajiro Imoto


Seismological Research Letters | 2017

The 2016 Kaikōura, New Zealand, Earthquake: Preliminary Seismological Report

Anna Kaiser; N. Balfour; Bill Fry; Caroline Holden; N. Litchfield; Matt Gerstenberger; E. D’Anastasio; Nick Horspool; Graeme H. McVerry; John Ristau; Stephen Bannister; A. Christophersen; Kate Clark; W. Power; David A. Rhoades; C. Massey; I. Hamling; L. Wallace; J. Mountjoy; Yoshihiro Kaneko; Rafael Benites; C. Van Houtte; S. Dellow; Liam Wotherspoon; K. Elwood; Ken Gledhill


Annals of Geophysics | 2010

Setting up an earthquake forecast experiment in Italy

Danijel Schorlemmer; A. Christophersen; Andrea Rovida; Francesco Mariano Mele; M. Stucchi; Warner Marzocchi


Geophysical Journal International | 2014

A new hybrid Coulomb/statistical model for forecasting aftershock rates

Sandy Steacy; Matt Gerstenberger; Charles Williams; David A. Rhoades; A. Christophersen


Bulletin of the Seismological Society of America | 2014

Regional Earthquake Likelihood Models II: Information Gains of Multiplicative Hybrids

David A. Rhoades; Matt Gerstenberger; A. Christophersen; Jeremy Douglas Zechar; Danijel Schorlemmer; M. Werner; Thomas H. Jordan


Geophysical Journal International | 2016

Retrospective tests of hybrid operational earthquake forecasting models for Canterbury

David A. Rhoades; M. Liukis; A. Christophersen; Matt Gerstenberger


Geophysical Journal International | 2016

Statistical estimation of the duration of aftershock sequences

Sebastian Hainzl; A. Christophersen; David A. Rhoades; David Harte

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Thomas H. Jordan

University of Southern California

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M. Werner

University of Bristol

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Danijel Schorlemmer

Southern California Earthquake Center

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Maria Liukis

Jet Propulsion Laboratory

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