Zhongwen Zhan

Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA

I joined Don Helmberger’s group in the summer of 2008, after getting a Master’s degree in China from Sidao Ni, another graduate student of Don’s. I was very excited,because Don has a giant academic family tree and I thought I would become Don’s last student, which is quite an honor in the Chinese culture, so-called the “final apprentice”. I was wrong! Don had another seven students after me and the final apprentice honor went to Voon-Hui Lai. Over Don’s long career, he had scores of students,many of whom are now big names in academia, especially in the United States and in China, because Don mentored a number of Chinese students.

I often wonder how Don could be so successful in training students and obviously I could not figure it out.But emotionally, one Chinese word often comes to my mind, that is “Shi Fu”. It may translate to “mentor”, but I am not sure that captures it very well. It has two characters, Shi and Fu, both very simple. Shi means teacher. Don was of course a great teacher. Well, I do not necessarily mean the Advanced Seismology class that I had to take three times to understand. In fact, after returning to the Caltech Seismo Lab in 2015, I co-taught the class a few times with Don and had to substantially update the materials. But Don taught us what maybe the most important thing in seismology: to love the wiggles. I am sure all his students had the experience of printing pages and pages of seismograms and looking at them one by one in Don’s office (e.g., Figure 1). Don absolutely loved them. Whenever I did not finish what I promised to do, I would just bring seismograms and Don would not remember to ask about the actual work. One of the most important tools to learn initially was “pssac” or “pssac2”,developed by previous students in Don’s group, to plot seismograms beautifully with GMT. Fortunately, I learned those tools with Sidao in China already so the transition into Don’s group was not too difficult.

Figure 1. Don Helmberger and the author reading seismograms together.

The second character in “Shi Fu” is “Fu”. “Fu” means father and I think it is appropriate here because Don’s students all respect and love him from the bottom of their hearts. Everyone probably has a different reason. For me,Don gave me so much trust and support to explore, more than what I feel I deserved. Even for the topics that he was not particularly interested in, he would still try his best to support me. My Master’s thesis was about ambient noise correlations, and Don could not care less about seismic noise. But instead of trying to convince me to stop working on noise, he put a lot of time to help me write my first paper in seismology about retrieving body waves from noise (Zhan ZW et al., 2010). Later Don suggested that I use ambient noise correlations to calibrate path effects and study earthquakes better (Zhan ZW et al., 2011), as a compromise of our research interests, which eventually moved me out of noise to several real earthquake projects(e.g., Zhan ZW et al., 2012, 2014a, b). However, Don’s attempt to guide me into deep Earth seismic modeling never went too far, partially because he was never very insistent. The hardest push you can expect from Don is a small sticker note on your screen that only has three words: “See me, Don”. On the other hand, whenever I talked to Don, I felt more confident, lifted, and on the edge of discovering something important from the wiggles so I wanted to work hard on the projects. This was even true in that summer of 2008, when my English was much worse.Don seemed to have the magic power to communicate with me with no problem. In fact, I think Don’s amazing skills with students was probably key to his long productive career, even after he could not play with data directly on next generation computers. Don always tried as much as he could to help the careers of his students and kept the connections going for years, sometimes decades. When I returned to the Seismo Lab in 2015 as a faculty member,he introduced me to many external funding opportunities,and we wrote several proposals together. In fact, the moment-tensor paper from the Air Force project Don and I co-PI-ed is about to be published (Jia Z et al., 2022).Maybe it is the last paper of Don’s.

Don was a great teacher and mentor, but he cared and gave more love to his students than he had to, and we loved him back. In some Kungfu movies they translate to“Master”. Certainly, Don was a grand master of seismology and at the same time, a grand master of mentoring. I will always remember him, miss him, and my time with him will keep inspiring myself to be a better mentor in the future.