My journey to the center of the Earth: A tribute to Professor Donald V. Helmberger

It has been more than a year since Don passed away suddenly.Thinking about it still makes my heart hurt.I did not know Don Helmberger or any other famous geophy...     

Donald V. Helmberger the Mentor

Don is certainly missed,by me,and by so many others.I particularly miss the constancy I derived by thinking of him down in Pasadena on the third floor of South ...     

In memory of Donald V. Helmberger

When I received the shocking news on August 13,2020 that our beloved Don passed away,I was deeply saddened.The feeling was worsened by the COVID-19 pandemic tha...     

Data and curiosity: Working with mentor Donald V. Helmberger

I arrived at Caltech in June 1986,with interests in both mineral physics and seismology.I was excited to either study mineral physics with Professor Tom Ahrens,...     

The Lost and the Found: Memories of Donald V. Helmberger

My first exposure to Don Helmberger's work was during a seismology class in my 2nd year in college where several students,including myself,were to present on Gr...     

Donald V. Helmberger,the master mentor: Testimonials from former international students

Don trained many Ph.D.students over the～5 decades of his career,at least 45 were advised or co-advised according to a Caltech account.A large number were intern...     

Donald V. Helmberger’s art and science of waveforms

I arrived at the Caltech Seismo Lab early in May 1972.The faculty and graduate students had the run of an old mansion(Donnelly Lab)that was slightly tattered ar...     

Graduate studies with Donald V. Helmberger

Arriving at the Seismo Lab in 1981,I first worked with Hiroo Kanamori on the seismotectonics of the New Hebrides(Vidale and Kanamori,1983)(I don't remember why)...     

Deep diving with Donald V. Helmberger

It has been more than a year since Don left us.He left us so suddenly.We planned to have a phone call after he settled down at his new house.However,it never ha...     

How Donald V. Helmberger inspired me

I first met Don Helmberger when I visited Caltech in the spring of 1984 as a prospective graduate student.During that visit,I was immediately impressed by Don's...     

A graduate student experience with Professor Donald V. Helmberger

A year after the passing of Don Helmberger,it is remarkable how memories of interactions with him over my entire professional career continue to spark affection...     

Recollections of my mentor,Donald V. Helmberger

I arrived at Caltech as a graduate student in the summer of 1979.With a BSc degree in physics,I knew little to nothing about seismology or geophysics.The Seismo...     

Preface to the special memorial issue for Professor Donald V. Helmberger

Donald Vincent Helmberger,Ph.D.and Smits Family Professor of Geophysics Emeritus at Caltech(Figure 1),one of the primary founders of seismic waveform modeling,w...     

Memories of Donald V. Helmberger: Mentor and seismologist extraordinaire

I grew up in one of the most aseismic regions of the planet but decided as a child that I wanted to be a seismologist.Ignoring all the naysayers who claimed tha...     

Development and testing of numerical methods for two-way nested air pollution modelling

A new 3-D model REGINA (REGIonal high resolutioN Air pollution model) is under development at the National Environmental Research Institute (NERI). The model is based on pieces from several models developed over the last decades at NERI. The aim of the work is to develop a nested model which can operate with very high resolution in both space and time. To fulfill this aim the choice and implementation of accurate numerical methods is crucial. The model will be applied for studying air pollution phenomena (both monitoring, forecasting and scenarios) over Denmark. The present paper is focussed on the modification, implementation and testing of a numerical method for treating the horizontal advection in the model as well as the implementation of two-way nesting techniques. The horizontal transport in the model is solved using an accurate space derivative algorithm. This method is traditionally implemented with periodic boundary conditions, however, this is not an option for nested modelling. A new method for calculating non-periodic boundary conditions has been developed in order to overcome this problem. Extensive testing of the numerical solution of the advection and the coupling of the solution of advection and chemistry in the model using Molenkamp–Crowley rotation tests have been carried out. The results show that the model with the current implementation of numerical methods is suitable for calculating air pollution levels with high resolution.     

Mesozoic and Cenozoic tectonics of the Møre Trøndelag Fault Complex,central Norway: constraints from new apatite fission track data

The Møre Trøndelag Fault Complex (MTFC) of central Norway is a long-lived structural zone whose tectonic history included dextral strike slip, sinistral strike slip, and vertical offset. Determination of an offset history for the MTFC is complicated by the lack of well preserved stratigraphic markers. However, low temperature apatite fission track (AFT) thermochronology offers important new clues by allowing the determination of exhumation histories for individual fault blocks presently exposed within the MTFC area. Previously published AFT data from crystalline basement in and near the MTFC suggest the region has a complicated pattern of exhumation. We present new AFT data from a NW–SE transect perpendicular to the principal structural grain of the MTFC. FT analyses of 15 apatite samples yielded apparent ages between 90 and 300 Ma, with mean FT length ranging from 11.8 to 13.5 μm. Thermal models based upon the age and track length data show the MTFC is comprised by multiple structural blocks with individual exhumation histories that are discrete at the 2σ confidence level. Thermal modeling of the AFT data indicates exhumation progressed from west to east, and that the final juxtaposition and exhumation of the innermost blocks took place during Cretaceous or Tertiary (possibly Neogene) time. We suggest that least some of the fracture lineaments of central Norway were re-activated during Mesozoic extension and the opening of the Norwegian sea, and may have remained active into the Cenozoic.     

2006年11月23日新疆乌苏5.1级地震及部分地震学前兆异常特征

介绍了2006年11月23日新疆乌苏5.1级地震的基本参数、震源机制解、地震序列特征、发震构造和局部构造应力场;分析了震前数字地震波参数的变化和部分地震学前兆异常特征。研究结果认为,乌苏5.1级地震是博罗科努-阿齐克库都克断裂发生右旋走滑错动所致。震前观察到震中附近P波初动半周期、P波与S波振幅比以及应力降的变化。震前震中附近曾出现4级地震集中分布、3级地震空区图像,震前6~9个月出现震群活动,震前2个月温泉地震窗异常。除上述异常外,乌苏5.1级地震前整体异常比例不高。     

Simulating spatiotemporal variations of atmospheric CO2 using a nested hemispheric model

A three-dimensional Eulerian nested model for transport, diffusion, and surface fluxes of CO₂ has been developed. The model is used to study the spatial and temporal variations of atmospheric CO₂ concentrations as a step towards a better understanding of the regional source pattern over Europe. The influence from the national surface characteristics, as e.g. fossil CO₂ emissions or ecosystem fluxes, can be treated on a continental or national level in the model. In the future the model can be used as a mean to corroborate national and EU-wide controls or reductions of carbon emissions. One of the major questions in the estimation of e.g. national CO₂ budgets is the quantification of surface ecosystem fluxes. In order to test the sensitivity of atmospheric CO₂ concentrations to ecosystem fluxes, two different parameterizations [J. Geophys. Res. 92 (1987) 2999] and [Global Biogeochem. Cycles 10 (1996) 269] have been implemented in the model. The model both with and without nest is validated by comparison with measurements and the different model results will be discussed. The results show that including a nested domain with higher spatial resolution significantly improves the model performance in some areas. In spite of regional deviations in the two sets of ecosystems fluxes no major differences are seen over Europe as a whole when either of the two parameterizations are included in the model and the results compared.     

Investigating Bermuda's pollution history through stable isotope analyses of modern and museum-held gorgonian corals

For centuries, Bermuda has been challenged with wastewater management for the protection of human and environmental health. By quantifying the δ¹⁵N of the common sea fan Gorgonia ventalina sampled from 30 sites throughout Bermuda we show that sewage-derived nitrogen is detectable on nearshore coral reefs and declines across the lagoon to the outer rim. We also sampled gorgonians from two museum collections representing a 50y time-series (1958–2008). These samples revealed an increase in δ¹⁵N of > 4.0‰ until the mid-1970s, after which δ¹⁵N values slowly declined by ~ 2.0‰. A δ¹⁵N chronology from a gorgonian skeleton exhibited a similar decline over the last 30–40 years of approximately 0.6‰. We conclude that policies have been effective in reducing sewage impacts to Bermudian reefs. However, significant sources of sewage pollution persist and are likely have a strong impact on harbor and nearshore coral communities and human health.